In the C# language specifications it explicitly states:

Delegates are similar to the concept of function pointers found in some other languages, but unlike function pointers, delegates are object-oriented and type-safe.

I understand delegates need to be a little more flexible than pointers because .NET moves memory around. That's the only difference I'm aware of, but I am not sure how this would turn a delegate into in OO concept...?

What makes a function pointer not object oriented? Are pointers and function pointers equivalent?

Well, Wikipedia says that "object oriented" means using "features such as data abstraction, encapsulation, messaging, modularity, polymorphism, and inheritance." Lacking a better definition, let's go with that.

Function pointers don't contain data, they don't encapsulate implementation details, they neither send nor receive messages, they are not modular, they are not typically used in a polymorphic manner (though I suppose they could in theory be covariant and contravariant in their return and formal parameter types, as delegates now are in C# 4) and they do not participate in an inheritance hierarchy. They are not self-describing; you can't ask a function pointer for its type because it doesn't have one.

By contrast, delegates capture data -- they hold on to the receiver. They support messaging in the sense that you can "message" a delegate by calling its ToString or GetType or Invoke or BeginInvoke methods to tell it to do something, and it "messages" you back with the result. Delegate types can be restricted to certain accessibility domains if you choose to do so. They are self-describing objects that have metadata and at runtime know their own type. They can be combined with other delegates. They can be used polymorphically as System.MulticastDelegate or System.Delegate, the types from which they inherit. And they can be used polymorphically in the sense that in C# 4 delegate types may be covariant and contravariant in their return and parameter types.

In .NET, using "foreach" to iterate an instance of IEnumerable will create a copy? So should I prefer to use "for" instead of "foreach"?

I wrote some code to testify this:

struct ValueTypeWithOneField
{
    private Int64 field1;
}

struct ValueTypeWithFiveField
{
    private Int64 field1;
    private Int64 field2;
    private Int64 field3;
    private Int64 field4;
    private Int64 field5;
}

public class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("one field");
        Test<ValueTypeWithOneField>();

        Console.WriteLine("-----------");

        Console.WriteLine("Five field");
        Test<ValueTypeWithFiveField>();

        Console.ReadLine();
    }

    static void Test<T>()
    {
        var test = new List<T>();
        for (int i = 0; i < 5000000; i++)
        {
            test.Add(default(T));
        }

        Stopwatch sw = new Stopwatch();

        for (int i = 0; i < 5; i++)
        {
            sw.Start();

            foreach (var item in test)
            {

            }

            sw.Stop();
            Console.WriteLine("foreach " + sw.ElapsedMilliseconds);
            sw.Restart();

            for (int j = 0; j < test.Count; j++)
            {
                T temp = test[j];
            }

            sw.Stop();
            Console.WriteLine("for " + sw.ElapsedMilliseconds);
            sw.Reset();
        }
    }}

And this is the result that I got after I ran the code:

    one field
    foreach 68
    for 72
    foreach 68
    for 72
    foreach 67
    for 72
    foreach 64
    for 73
    foreach 68
    for 72
    -----------
    Five field
    foreach 272
    for 193
    foreach 273
    for 191
    foreach 272
    for 190
    foreach 271
    for 190
    foreach 275
    for 188

As we can see in the result, "foreach" always takes more time than "for".

So should I prefer to use "for" instead of "foreach" when iterating through a generic collection of value type?

Note: thanks for the reminder, I edited the code and result. but still, foreach is running slower than for.

Your test is not accurate; in the foreach version, you're actually spinning up the enumerator and retrieving each value from the list (even though you aren't using it). In the for version, you aren't doing anything with the list at all, other than looking at its Count property. You're essentially testing the performance of an enumerator traversing a collection compared to incrementing an integer variable an equivalent number of times.

To create parity, you'd need to declare a temporary variable and assign it in each iteration of the for loop.

That being said, the answer to your question is yes. A copy of the value will be created with every assignment or return statement.

Performance

This pseudocode breakdown should explain why foreach is somewhat slower than using for in this particular instance:

foreach:

try
{
    var en = test.GetEnumerator(); //creates a ListEnumerator
    T item;

    while(en.MoveNext()) // MoveNext increments the current index and returns
                         // true if the new index is valid, or false if it's
                         // beyond the end of the list. If it returns true,
                         // it retrieves the value at that index and holds it 
                         // in an instance variable
    {
        item = en.Current; // Current retrieves the value of the current instance
                           // variable
    }
}
finally { }

for:

int index = -1;
T item;

while(++index < test.Count)
{
    item = test[index];
}

As you can see, there's simply less code in the for implementation, and foreach has a layer of abstraction (the enumerator) on top of the for. I wrote the for using a while loop to show the two versions in a similar representation.

With all that said...

You're talking about a trivial difference in execution time. Use the loop that makes the code clearer and smaller, and in this circumstance that looks like foreach.

How do I pass 2 lists into Parallel.ForEach?

Example:

List<Person> a = new List<Person>() { new Person(), new Person(), new Person() };
List<Car> b = new List<Car>() { new Car(), new Car(), new Car() };

//PSEUDO CODE
Parallel.ForEach(a, b, (person, car) => {
    //WORK ON person, WORK ON car
});  

I would prefer to avoid encapsulating Person and Car into Object container. Is this possible?

Thanks for any help!

If you're using .NET 4 (which you probably are) and you're trying to pair the first Person with the first Car etc, you can just use Zip:

List<Person> a = new List<Person>() { new Person(), new Person(), new Person() };
List<Car> b = new List<Car>() {} { new Car(), new Car(), new Car() };
var zipped = a.Zip(b, (person, car) => new { person, car });

Parallel.ForEach(zipped, pair => {
    Person person = pair.person;
    Car car = pair.car;
});

I'm looking for a way to write code that tests whether a value is boxed.

My preliminary investigations indicate that .NET goes out of its way to conceal the fact, meaning that GetType() and IsValueType don't reveal the difference between a boxed value and an unboxed value. For example, in the following LinqPad C# expressions, I have faith that o1 is boxed and i1 is not boxed, but I would like a way to test it in code, or, second best, a way to know FOR SURE when looking at any variable or value, even if its type is "dynamic" or "object," whether it's boxed or not boxed.

Advice, please & thanks?

// boxed? -- no way to tell from these answers!
object o1 = 123;
o1.GetType().Dump("o1.GetType()");
o1.GetType().IsValueType.Dump("o1.GetType().IsValueType");

// not boxed? -- no way to tell from these answers!
int i1 = 123;
i1.GetType().Dump("i1.GetType()");
i1.GetType().IsValueType.Dump("i1.GetType().IsValueType");

Here are some simple helper methods to check if a variable is a boxed integer:

public static bool IsBoxed(object item)
{
    return true;
}

public static bool IsBoxed<T>(T item) where T : struct
{
    return false;
}

Just call IsBoxed(...) on your variable:

IsBoxed(o1) // evaluates to true
IsBoxed(i1) // evaluates to false

This accomplishes nothing, of course. Why exactly do you need to know if a value is boxed or not?

Why does ICustomAttributeProvider.GetCustomAttributes() return object[] instead of Attribute[]?

Is there any circumstance when using the ICustomAttributeProvider implementations from mscorlib and System assemblies will return objects that are not of type Attribute?

The CLI spec (ECMA 335) Partition II, Clause 21 states in part:

While any user-defined type can be used as an attribute, CLS compliance requires that attributes will be instances of types whose base class is System.Attribute.

In other words, a language that is not CLS-compliant may allow you to specify attributes that do not derive from Attribute, so the GetCustomAttributes method is probably designed to allow such attributes to be consumed.

I'm pretty sure that no such non-CLS-compliant language exists, and .NET doesn't support it, but one can imagine that the designers of Reflection did not want to preclude the possibility in the future.

As for your second question, a quick inspection of the source code for System.Reflection shows that you always get an Attribute[] back. Since the returned objects are always Attribute[], you can safely cast them, but there's no guarantee that it will always work that way.

I need your help with a little problem. I have four labels and I want to display on them random value between 0 to 100, and the sum of them must be 100.

This is my code :

private void randomly_Click(object sender, EventArgs e)
{
    double alpha = 0, beta = 0, gamma = 0, delta = 0;
    double temp;
    int tempDouble;

    Random rnd = new Random();

    alpha = rnd.Next(0, 100);

    temp = 100 - alpha;
    tempDouble = (int)temp;
    beta = rnd.Next(0, tempDouble);

    temp = 100 - (alpha + beta);
    tempDouble = (int)temp;
    gamma = rnd.Next(0, tempDouble);

    temp = 100 - (alpha + beta + gamma);
    tempDouble = (int)temp;
    delta = rnd.Next(0, tempDouble);

    temp = alpha + beta + delta + gamma;
    temp = 100 - temp;
    temp = temp / 4;

    alpha = alpha + temp;
    beta = beta + temp;
    gamma = gamma + temp;
    delta = delta + temp;

    cInsertion.Text = alpha.ToString();
    cMoyens.Text = beta.ToString();
    cInternational.Text = gamma.ToString();
    cRecherche.Text = delta.ToString();
}   

The problem is that I'm giving to the alpha the chance to have the biggest value, and for delta the lowest value.

Is there any way to give them all the same chance to have a real random value?

You could do something like this:

double alpha = 0, beta = 0, gamma = 0, delta = 0, k = 0;
Random rnd = new Random();

alpha = rnd.Next(0, 100);
beta = rnd.Next(0, 100);
gamma = rnd.Next(0, 100);
delta = rnd.Next(0, 100);

k = (alpha + beta + gamma + delta) / 100;

alpha /= k;
beta /= k;
gamma /= k;
delta /= k;

cInsertion.Text = alpha.ToString();
cMoyens.Text = beta.ToString();
cInternational.Text = gamma.ToString();
cRecherche.Text = delta.ToString();

This way you're saying let's take a random value for all 4 variables, and then we'll scale them by a factor k that'll make their sum be 100.

I have class called Chicken and in Chicken I have some methods, so in another class where I instantiate and call methods on Chicken, I might do something like this:

Chicken chicken = new Chicken("Name","Description")


public void UpdateChicken(Chicken chicken)
{ 
   chicken.Update(chicken);
}

Is the above fine or does it present problems, if so, is it better to have another class, such as ChickenCalculations and do something like:

public void UpdateChick(Chicken chicken)
{
    ChickenCalculations.Update(chicken);
}

Here is an implementation:

Chicken chicken = new Chicken("Bob","Coolest Chicken", 4, 123, 5, 388, true, false, true);

Chicken anotherChicken = new Chicken()
anotherChicken.Update(chicken);
chicken.Update(chicken)

Here is a more practical example instead of using a Chicken:

public class AirlineBooking
{
    int BookingId {get;set;}
    string Name {get;set;}
    string Description {get;set;}
    decimal Price {get;set;}
    decimal Tax {get;set;}
    string seat {get;set;}
    bool IsActive {get;set;}
    bool IsCanceld {get;set;}


    public AirlineBooking(string name, string description, decimal price, 
                          decimal tax, string seat, bool isActive, bool isCanceled)
    {
        Name = name;
        Description = description;
        Price = price;
        Tax = tax;
        Seat = seat;
        IsActive = isActive;
        IsCanceled = isCanceled;
    }

    public Update(AirlineBooking airlineBooking, int id)
    {
          //Call stored proc here to update booking by id
    }

    public class BookingSystem
    {
       //Create new booking
       AirlineBooking booking = new AirlineBooking("ticket-1",
                                                   "desc",150.2,22.0,
                                                   "22A",true, false);

       //Change properties and update.
       booking.Name ="ticket-2";
       booking.Description = "desc2";
       booking.Price = 200.52;
       booking.Tax = 38.50;

       public void UpdateBooking(AirlineBooking booking, int id)
       {
            /* This is the meat of the question, should the passed in booking to
               update itself or should I have a Service Class , such as
               AirlineBookingOperations with an update method. */
            booking.Update(booking,id);
       }
    }
}

Why isn't the UpdateChicken function a member of the Chicken class?

That way, you wouldn't have to pass in an instance of a Chicken object, but rather just call the Update method on an existing instance:

Chicken chicken = new Chicken("Name", "Description");
chicken.Update();

It's generally best to encapsulate all the methods that operate on a particular class inside of that class, rather than splitting them up into a separate "helper" class. Let them chickens manage themselves!

I've found a difference in overload resolution between the C# and the VB-compiler. I'm not sure if it's an error or by design:

Public Class Class1
    Public Sub ThisBreaks()
        ' these works '
        Foo(Of String)(Function() String.Empty) 'expression overload '
        Foo(String.Empty) 'T overload '

        ' this breaks '
        Foo(Function() String.Empty)
    End Sub

    Public Sub Foo(Of T)(ByVal value As T)

    End Sub

    Public Sub Foo(Of T)(ByVal expression As Expression(Of Func(Of T)))

    End Sub
End Class

Note that it doesn't matter if the overloaded Foo-methods are defined in VB or not, the only thing that matters is that the call site is in VB.

The VB-compiler will report an error:

Overload resolution failed because no accessible 'Foo' is most specific for these arguments:

'Public Sub Foo(Of String)(expression As System.Linq.Expressions.Expression(Of System.Func(Of String)))': Not most specific.

'Public Sub Foo(Of )(value As )': Not most specific.

---

Adding the C# code which works for comparison:

class Class1
{
    public void ThisDoesntBreakInCSharp()
    {
        Foo<string>(() => string.Empty);
        Foo(string.Empty);
        Foo(() => string.Empty);
    }

    public void Foo<T>(T value)
    {

    }

    public void Foo<T>(Expression<Func<T>> expression)
    {

    }
}

I'm pretty sure I've found the reason for this and it is not a short coming of the VB-compiler but it is a short coming of the C# compiler.

Consider the following which is legal in VB:

Dim foo = Function() String.Empty

The equivalent would not be legal in c#:

var foo = () => string.Empty;

So, type inference is a bit stronger in VB, because of this the argument in the example Function() String.Empty can be inferred to Function(Of String) which would be applicable to the Foo(Of T)(ByVal value As T) overload.

In C# this can not happen since the () => string.Empty can never be inferred without context, it can be inferred in the expression overload but not in the T-overload.

I'm working on a library that allows users to input arbitrary expressions. My library then compiles those expressions as part of a larger expression into a delegate. Now, for still unknown reasons compiling the expression with Compile sometimes/often results in code that is far slower than it would be if it weren't a compiled expression. I asked a question about this before and one workaround was to not use Compile, but CompileToMethod and create a static method on a new type in a new dynamic assembly. That works and the code is fast.

But users can input arbitrary expressions and it turns out that if the user calls a non-public function or accesses a non-public field in the expression, it throws a System.MethodAccessException (in the case of a non-public method) when the delegate is invoked.

What I could probably do here is create a new ExpressionVisitor that checks if the expression accesses anything non-public and use the slower Compile in those cases, but I'd rather have that the dynamic assembly somehow gets the rights to access the non-public members. Or find out if there's anything I can do about Compile being slower (sometimes).

The full code to reproduce this problem:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using System.Reflection;
using System.Reflection.Emit;

namespace DynamicAssembly
{
  public class Program
  {
    private static int GetValue()
    {
      return 1;
    }

    public static int GetValuePublic()
    {
      return 1;
    }

    public static int Foo;

    static void Main(string[] args)
    {
      Expression<Func<int>> expression = () => 10 + GetValue();

      Foo = expression.Compile()();

      Console.WriteLine("This works, value: " + Foo);

      Expression<Func<int>> expressionPublic = () => 10 + GetValuePublic();

      var compiledDynamicAssemblyPublic = (Func<int>)CompileExpression(expressionPublic);

      Foo = compiledDynamicAssemblyPublic();

      Console.WriteLine("This works too, value: " + Foo);

      var compiledDynamicAssemblyNonPublic = (Func<int>)CompileExpression(expression);

      Console.WriteLine("This crashes");

      Foo = compiledDynamicAssemblyNonPublic();
    }

    static Delegate CompileExpression(LambdaExpression expression)
    {
      var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
        new AssemblyName("MyAssembly"+ Guid.NewGuid().ToString("N")), 
        AssemblyBuilderAccess.Run);

      var moduleBuilder = assemblyBuilder.DefineDynamicModule("Module");

      var typeBuilder = moduleBuilder.DefineType("MyType", TypeAttributes.Public);

      var methodBuilder = typeBuilder.DefineMethod("MyMethod", 
        MethodAttributes.Public | MethodAttributes.Static);

      expression.CompileToMethod(methodBuilder);

      var resultingType = typeBuilder.CreateType();

      var function = Delegate.CreateDelegate(expression.Type, 
        resultingType.GetMethod("MyMethod"));

      return function;
    }
  }
}

The problem is not permissions because there is no permission that can allow you to access a non-public field or member of another class without reflection. This is analogous to the situation where you compiled two non-dynamic assemblies and one assembly calls a public method in the second assembly. Then if you change the method to private without recompiling the first assembly, the first assemblies call will now fail at runtime. In other words the expression in your dynamic assembly is being compiled into an ordinary method call which it doesn't have permission to call anymore than you do from another class even in the same assembly.

Since no permission can solve your problem, you might be able to transform non-public field and method references into subexpressions that use reflection.

Here is an example taken from your test case. This fails:

Expression<Func<int>> expression = () => 10 + GetValue();

but this will succeed:

Expression<Func<int>> expression = () => 10 + (int)typeof(Program).GetMethod("GetValue", BindingFlags.Static | BindingFlags.NonPublic).Invoke(null, null);

Since this does not crash with an exception, you can see that your dynamic assembly does have reflection permission and it can access the private method, it just can't do it using an ordinary method call that CompileToMethod results in.

We developed an application using .net 2.0. We license our software which means whenever we release a new version, we have to push out the change to all our existing clients.

No one in my group has the slightest motivation to upgrade to a newer version of .net. They simple see it as more work for our support team to deploy and argue that clients will be resistant to any change.

Can anyone point me in the direction of some argument i could present to Non programmers that might sway them.

If noting else, some argument that it is safe, and will not cause our clients any harm who already have the .net 2.0 framework on their machines?

I figure it's hopeless. I'm gonna be stuck using the .net 2.0 framework until for another 4 or 5 years i bet... perhaps longer :( help!

I really want to be able to use WCF, LINQ, WPF (possible), and the option to use the Entity Framework 4.0.!

thanks

jonathan

I tend to agree with @Lior Kogan, in that upgrading for the sake of it is not something that you should be arguing with management about.

In fact, there are good arguments for not upgrading:

• if you've got a stable platform, why introduce potential instability?
• if we upgrade this, will it force us to spend more money upgrading other things?
• will it mean we have to force our customers to upgrade as well?

All these things are big negatives to a business, and make a good case for maintaining the status-quo.

However, upgrades are necessary at some point. There are a lot of very frustrated web developers out there who are cursing businesses worldwide for taking the above aproach to Internet Explorer v6: While those businesses were arguably doing the right thing for some time, they've now passed the point where it is difficult to defend staying still. It may not be the case for you now, but eventually the same will hold true for a .NET upgrade.

The argument here would be that the old version of the technology is obsolete:

• it is no longer supported by the vendor, particularly with security fixes.
• it is no longer sold by the vendor, making it hard to increase your number of users.
• other technologies that we use rely on the newer version.
• our customers are asking us for features that can only be delivered using the new version.

If any one of those points holds true than you may have a good argument for an upgrade that will win over the management. If not, you may have to stick it out.

I'm using the new MemoryCache in .Net 4, with a max cache size limit in MB (I've tested it set between 10 and 200MB, on systems with between 1.75 and 8GB of memory). I don't set any time based expiration on the objects, as I'm using the cache simply as a high performance drive, and as long as there is space, I want it used. To my surprise, the cache refused to evict any objects, to the point that I would get SystemOutOfMemory exceptions.

I fired up perfmon, wired up my application to .Net CLR Memory\#Bytes In All Heaps, .Net Memory Cache 4.0, and Process\Private Bytes -- indeed, the memory consumption was out of control, and no cache trims were being registered.

Did some googling and stackoverflowing, downloaded and attached the CLRProfiler, and wham: evictions everywhere! The memory stayed within reasonable bounds based upon the memory size limit I had set. Ran it in debug mode again, no evictions. CLRProfiler again, evictions.

I finally noticed that the profiler forced the application to run without concurrent garbage collection (also see useful SO Concurrent Garbage Collection Question). I turned it off in my app.config, and, sure enough, evictions!

This seems like at best an outrageous lack of documentation to not say: this only works with non-concurrent garbage collection -- though I image since its ported from ASP.NET, they may not have had to worry about concurrent garbage collection.

So has anyone else seen this? I'd love to get some other experiences out there, and maybe some more educated insights.

---

Update 1

I've reproduced the issue within a single method: it seems that the cache must be written to in parallel for the cache evictions not to fire (in concurrent garbage collection mode). If there is some interest, I'll upload the test code to a public repo. I'm definitely getting toward the deep end of the the CLR/GC/MemoryCache pool, and I think I forgot my floaties...

---

Update 2

I published test code on CodePlex to reproduce the issue. Also, possibly of interest, the original production code runs in Azure, as a Worker Role. Interesting, changing the GC concurrency setting in the role's app.config has no effect. Possibly Azure overrides GC settings much like ASP.NET? Further, running the test code under WPF vs a Console application will produce slightly different eviction results.

You can "force" a garbage collection right after the problematic method and see if the problem reproduces executing:

System.Threading.Thread.Sleep(200);
GC.Collect();
GC.WaitForPendingFinalizers();

right at the end of the method (make sure that you free any handles to reference objects and null them out). If this prevents memory leakage, and then yes, there may be a runtime bug.

Possible Duplicate:
C# okay with comparing value types to null

If I try to assign null to a non-nullable type in C#:

System.DateTime time = null;

I'll get a compile-time error:

error CS0037: Cannot convert null to 'System.DateTime' because it is a non-nullable value type

which makes sense. But if compare the same type against null:

System.DateTime time = obtainFromSomewhere();
if( time == null ) {
    //whatever;
}

there's no compile-time error. This doesn't make sense to me - if I can't assign null then why would it ever be null?

Why am I allowed to compare a non-nullable type with null?

The reason this works for DateTime, is because DateTime defines it own == operator. Because it does so, it gets a lifted version of the operator which may be used with DateTime?. Since both DateTime and null may be implicitly converted to DateTime?, the comparison compiles but will always evaluate to false at runtime.

Thanks to Matt Ellen for pointing out the fact that my original answer didn't cover the example in the question.

A curious case of Visual Studio 2010 debugger(it can not hit a break point)

This is the code that reproduces the problem:

class Program
{
static void Main(string[] args)
{
    bool b = false;

    if (b)
    {
        List<string> list = new List<string>();
        foreach (var item in list)
        {

        }
    }
    else
    {
        Console.WriteLine("1");
    }
    Console.WriteLine("2");//add a break point here in VS2010
}
//1. configuration: release
//2. platform target: x64 or Any Cpu
//3. debug info: pdb only or full
//4. OS: Win7 x64
//5. optimize code: enabled
}

Add a break point to the last statement of the code, then debug it in vs2010, you'll see that the break point can not be hit.

To reproduce this curious case, you'll need to meet the following conditions:

1. Operation system: windows 7 x64;

   2.VS build configuration: release;

   3.VS build platform target: x64 or Any Cpu;

   4.VS build debug info: pdb only or full;

   5.VS build optimize code: enabled;

I am not sure those conditions are sufficient to reproduce it, but it's how my machine was configured when I found this issue.

Why is the debugger not able to hit the break point?

Thanks in advance.

And if you can reproduce this issue, please consider to vote on this post: http://connect.microsoft.com/VisualStudio/feedback/details/664400/a-curious-case-of-visual-studio-2010-debugger-it-can-not-hit-a-break-point#tabs

When the provided example is built in release mode and then JIT-ed into 64-bit machine code, it does not contain enough information for the debugger to correlate the breakpoint with any particular machine instruction. That’s why debugger never stops at this breakpoint during execution of a JIT-ed machine code. It just does not know where to stop. Probably it is some kind of misbehavior or even a bug in 64-bit CLR debugger because it is reproducible only when it is JIT-ed into 64-bit machine code but not into 32-bit machine code.

When the debugger sees a breakpoint in your code it tries to find out a machine instruction in the JIT-ed code that corresponds to the location marked by the breakpoint. First, it needs to find an IL instruction that corresponds to a breakpoint location in your C# code. Then it needs to find a machine instruction that corresponds to the IL command. Then it sets a real breakpoint on the found machine instruction and starts execution of the method. In your case, it looks like that the debugger just ignores a breakpoint because it cannot map it to a particular machine instruction.

The debugger cannot find an address of a machine instruction that immediately follows if…else statement. The if…else statement and the code inside it somehow causes this behavior. It does not matter what statement follows the if…else. You can replace the Console.WriteLine(“2”) statement with some other one and you will be still able to reproduce the issue.

You will see that the C# compiler emits a try…catch block around the logic that reads the list if you will disassemble the resulting assembly with Reflector. It is a documented feature of the C# compiler. You can read more about it at The foreach statement

A try…catch…finally block has a pretty invasive effect on a JIT-ed code. It uses the Windows SEH mechanism under the hood and rewrites your code badly. I cannot find a link to a good article right now but I’m sure that you can find one out there if you are interested.

It is what happens here. The try…finally block inside of if…else statement causes the debugger to hiccup. You can reproduce your issue with a much simple code.

bool b = false;
        if (b)
        {
            try
            {
                b = true;
            }
            finally
            {
                b = true;
            }
        }
        else
        {
            b = true;
        }
        b = true;

This code does not call any external functions (it eliminates effect of method inlining proposed by one of the answers) and it compiles directly into IL without any additional coded added by the C# compiler.

It is reproducible only in release mode because in the debug mode the compiler emits the IL NOP instruction for every line of your C# code. The IL NOP instruction does nothing and it is directly compiled to the CPU NOP instruction by the JITer that does nothing too. The usefulness of this instruction is that it can be used by the debugger as an anchor for breakpoints even if the rest of the code is badly rewritten by the JITer.

I was able to make the debugger to work correctly by putting one NOP instruction right before the statement that follows the if…else.

You can read more about NOP operations and debugger mapping process here Debugging IL

You can try to use WinDbg and SOS extension for it to examine JIT-ed version of the method. You can try to examine machine code that JIT-er generates and try to understand why it cannot map back that machine code to particular line of C#.

Here are couple link about using WinDbg for breaking in managed code and getting a memory address of a JIT-ed method. I believe that you should be able to find a way to get JIT-ed code for a method from there: Setting a breakpoint in WinDbg for Managed Code, SOS Cheat Sheet (.NET 2.0/3.0/3.5).

You can also try to report an issue to Microsoft. Probably this is a CLR debugger bug.

Thank you for the interesting question.

I'm trying to get my head around the thought process when designing a large scale application.

Let's say I have a client who needs a new customer website and he is estimating 40,000 orders per day with an already 25,000 user base. When desiging the application, how do you about determining if a distributed architecutre is needed? Should I use a web farm? etc.

I've mostly build 2 tier (physical) applications in the past and I really want to improve my understanding.

Any insight would be great!

It's going to depend on a lot of other factors than just the number of orders per day. Where will it be hosted? What does that physical architecture look like? What else does the application do besides ecommerce? Does it need to integrate with other applications (besides the payment gateways of course)? Etc.

A simple two tier application in the right cloud hosting environment (say VMware for instance) that can scale dynamically would work just fine for an ecommerce website. A simple two tier application in the right on-premises hosting environment (load balanced web farm) should also work fine for an ecommerce website. It's the difference between scaling up (potentially hidden with virtualization, which ends up being a scale out of sorts) and scaling out (adding more servers).

A distributed architecture would allow you to distribute the system load (say order processing) to 1:M servers that sit (perhaps) behind a load balancer. This is a very common approach, and would also work very well for an ecommerce website.

In my opinion, there isn't one architecture or system design that fits every mold. The closest architecture to fit every mold (again, my opinion) would be a service oriented architecture. If all business processes and logic are services (and designed correctly), then no matter how your requirements change, no matter what your hosting environment looks like or changes to, and no matter what integration requirements you have, your system can handle it with little or no changes.

I'm trying to follow the MVVM pattern in a WPF application as good as I can, mainly to be able to create unit tests for my ViewModel logic.

In most cases data binding between ViewModel properties and properties of visual elements works fine and is easy. But sometimes I encounter situations where I cannot see an obvious and straightforward way while a solution to access and manipulate controls from code-behind is very easy.

Here is an example of what I mean: Inserting a text fragment into a TextBox at the current caret position

Since CaretIndex isn't a dependency property it can't be bound directly to a ViewModel's property. Here is a solution to work around this limitation by creating a dependency property. And here is the solution to do this in code-behind. I would prefer the code-behind way in this situation. Another problem I recently had was binding a dynamic collection of columns to a WPF datagrid. It was clear and simple to program in code-behind. But for a MVVM-friendly databinding approach I could only find work arounds in several blogs which all looked quite complex to me and had various limitations in one or the other aspect.

I don't want to keep the MVVM architecture clean of code-behind logic at all costs. If the amount of work arounds is too big, a MVVM-friendly solution requires a lot of code which I don't fully understand (I'm still a WPF beginner) and is too time consuming I prefer a code-behind solution and sacrifice automatic testability of a few parts of my application.

For the mentioned pragmatic reasons I am looking now for "patterns" to make controlled use of code-behind in an application without breaking the MVVM architecture or without breaking it too much.

Up to now I've found and tested two solutions. I will draw rough sketches with the Caret Position example:

Solution 1) Give the ViewModel a reference to the View through an abstract interface

• I would have an interface with methods which would be implemented by the view:

  public interface IView
  {
      void InsertTextAtCaretPosition(string text);
  }
  
  public partial class View : UserControl, IView
  {
      public View()
      {
          InitializeComponent();
      }
  
      // Interface implementation
      public void InsertTextAtCaretPosition(string text)
      {
          MyTextBox.Text = MyTextBox.Text.Insert(MyTextBox.CaretIndex, text);
      }
  }
  

• Inject this interface into the ViewModel

  public class ViewModel : ViewModelBase
  {
      private readonly IView _view;
  
      public ViewModel(IView view)
      {
          _view = view;
      }
  }
  

• Execute code-behind from a ViewModel's command handler through the interface methods

  public ICommand InsertCommand { get; private set; }
  // Bound for instance to a button command
  
  // Command handler
  private void InsertText(string text)
  {
      _view.InsertTextAtCaretPosition(text);
  }
  

To create a View-ViewModel pair I would use dependency injection to instantiate the concrete View and inject it into the ViewModel.

Solution 2) Execute code-behind methods through events

• The ViewModel is publisher of special events and command handlers raise those events

  public class ViewModel : ViewModelBase
  {
      public ViewModel()
      {
      }
  
      public event InsertTextEventHandler InsertTextEvent;
  
      // Command handler
      private void InsertText(string text)
      {
          InsertTextEventHandler handler = InsertTextEvent;
          if (handler != null)
              handler(this, new InsertTextEventArgs(text));
      }
  }
  

• The View subscribes to these events

  public partial class View : UserControl
  {
      public View()
      {
          InitializeComponent();
      }
  
      private void UserControl_Loaded(object sender, RoutedEventArgs e)
      {
          ViewModel viewModel = DataContext as ViewModel;
          if (viewModel != null)
              viewModel.InsertTextEvent += OnInsertTextEvent;
      }
  
      private void UserControl_Unloaded(object sender, RoutedEventArgs e)
      {
          ViewModel viewModel = DataContext as ViewModel;
          if (viewModel != null)
              viewModel.InsertTextEvent -= OnInsertTextEvent;
      }
  
      private void OnInsertTextEvent(object sender, InsertTextEventArgs e)
      {
          MyTextBox.Text = MyTextBox.Text.Insert(MyTextBox.CaretIndex, e.Text);
      }
  }
  

I am not sure if the Loaded and Unloaded events of the UserControl are good places to subscribe and unsubscribe to the events but I couldn't find problems during test.

I have tested both approaches in two simple examples and they both seem to work. Now my questions are:

1. Which approach do you think is preferable? Are there any benefits or downsides of one of the solutions which I possibly don't see?

2. Do you see (and perhaps practice) other solutions?

Thank you for feedback in advance!

Developing WPF applications I found both ways useful. If you need just one call from ViewModel to View, the second option, with event handler, looks simpler and good enough. But if you are requiring more complex interface between these layers, then it makes sense to introduce interface.

And my personal preference is to revert your option one and have a IViewAware interface implemented by my ViewModel and inject this ViewModel into View. Looks like an option three.

public interface IViewAware
{
    void ViewActivated();
    void ViewDeactivated();

    event Action CloseView;
}

public class TaskViewModel : ViewModelBase, IViewAware
{

    private void FireCloseRequest()
    {
        var handler = CloseView;
        if (handler != null)
            handler();
    }

    #region Implementation of IViewAware        
    public void ViewActivated()
    {
        // Do something 
    }

    public void ViewDeactivated()
    {
        // Do something 
    }

    public event Action CloseView;    
    #endregion
}

And this a simplified code for your View:

    public View(IViewAware viewModel) : this()
    {
        _viewModel = viewModel;

        DataContext = viewModel;
        Loaded += ViewLoaded;

    }

    void ViewLoaded(object sender, RoutedEventArgs e)
    {
        Activated += (o, v) => _viewModel.ViewActivated();
        Deactivated += (o, v) => _viewModel.ViewDeactivated();

        _viewModel.CloseView += Close;
    }

In real application I usually use an external logic to connect V and VM, for example Attached Behaviors.

Hello all,

I have a C sharp console application that captures a screenshot of a MS Word document serveral times. It works great, but when I place this application on a remote windows XP machine it works fine whilst I am remoted in i.e. my remote desktop is visible but if I run my app and leave remote desktop (minimize it, not even log off which I want to do) the screenshots it takes are blank!

The Screenshot app is being run by a service that runs as SYSTEM user.

How can I keep the GUI alive for windows even when there are no users connected?

Here is the code I use:

public Image CaptureWindow(IntPtr handle)
{
    // get te hDC of the target window
    IntPtr hdcSrc = User32.GetWindowDC(handle);
    // get the size
    User32.RECT windowRect = new User32.RECT();
    User32.GetWindowRect(handle, ref windowRect);
    int width = windowRect.right - windowRect.left;
    int height = windowRect.bottom - windowRect.top;
    // create a device context we can copy to
    IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
    // create a bitmap we can copy it to,
    // using GetDeviceCaps to get the width/height
    IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, width, height);
    // select the bitmap object
    IntPtr hOld = GDI32.SelectObject(hdcDest, hBitmap);
    // bitblt over
    GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);
    // restore selection
    GDI32.SelectObject(hdcDest, hOld);
    // clean up 
    GDI32.DeleteDC(hdcDest);
    User32.ReleaseDC(handle, hdcSrc);

    // get a .NET image object for it
    Image img = Image.FromHbitmap(hBitmap);
    // free up the Bitmap object
    GDI32.DeleteObject(hBitmap);

    return img;
}

Thanks all for any help.

Update

I am currently making use of PrintWindow which is the only thing that has come the closest as it manages to capture the window frame (i.e the minimise, maxmise and close buttons) but the inner part is black.

Although it hasn't fully worked, its proved to me that it is possible to create an image from a window handle whilst the application isn't even visible to a user.

Some time ago we were doing something similar, and we found that when RDC is minimized, the remote desktop session is not redrawn or accept keys or mouse events. Everything was working fine until we minimized the RDC screen. A colleague found out that this is done for performance reasons.

Some days ago I stumbled upon this, but I haven't had the chance to try it. If you try and it works, please let me know :)

Interacting with remote desktop when RDC is minimized

Regarding your comments: I think this is another kind of issue... I understand that you need your application to work even if no one is logged into the machine. I've implemented services that are allowed to interact with the desktop, for example, to launch an application and automate it. Even no one is logged in the machine, you can still manipulate the UI, for example, with an UI automation library (or your code, I assume).

After starting the machine, when my service and automated application are running everything works fine. Later on, the UI being automated will appear on the desktop of the first person who logs in (I was a machine administrator, I don't know what will happen when somebody with less privileges logs in).

I don't know what will happen if the first login is done through RDC. Maybe you could try changing those RDC settings id this affects the behavior of your application. Another option is:

1. Disable RDC and configure windows to Autologin with an specified account
2. Connect to this machine using another remote desktop application (e.g. TightVNC)

Does this help?

This is my first post on StackOverflow, so please bear with me. And I apologize upfront if my code example is a bit long.

Using C# and LINQ, I'm trying to identify a series of third level id elements (000049 in this case) in a much larger XML file. Each third level id is unique, and the ones I want are based on a series of descendant info for each. More specifically, if type == A and location type(old) == vault and location type(new) == out, then I want to select that id. Below is the XML and C# code that I'm using.

In general my code works. As written below it will return an id of 000049 twice, which is correct. However, I have found a glitch. If I remove the first history block that contains type == A, my code still returns an id of 000049 twice when it should only return it once. I know why it is happening, but I can't figure out a better way to run the query. Is there a better way to run my query to get the output I want and still use LINQ?

My XML:

<?xml version="1.0" encoding="ISO8859-1" ?>
<data type="historylist">
    <date type="runtime">
        <year>2011</year>
        <month>04</month>
        <day>22</day>
        <dayname>Friday</dayname>
        <hour>15</hour>
        <minutes>24</minutes>
        <seconds>46</seconds>
    </date>
    <customer>
        <id>0001</id>
        <description>customer</description>
        <mediatype>
            <id>kit</id>
            <description>customer kit</description>
            <volume>
                <id>000049</id>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>03</hour>
                        <minutes>00</minutes>
                        <seconds>02</seconds>
                    </date>
                    <userid>batch</userid>
                    <type>OD</type>
                    <location type="old">
                        <repository>vault</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>06</hour>
                        <minutes>43</minutes>
                        <seconds>33</seconds>
                    </date>
                    <userid>vaultred</userid>
                    <type>A</type>
                    <location type="old">
                        <repository>vault</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>06</hour>
                        <minutes>43</minutes>
                        <seconds>33</seconds>
                    </date>
                    <userid>vaultred</userid>
                    <type>S</type>
                    <location type="old">
                        <repository>vault</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>06</hour>
                        <minutes>45</minutes>
                        <seconds>00</seconds>
                    </date>
                    <userid>batch</userid>
                    <type>O</type>
                    <location type="old">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>site</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>11</hour>
                        <minutes>25</minutes>
                        <seconds>59</seconds>
                    </date>
                    <userid>ihcmdm</userid>
                    <type>A</type>
                    <location type="old">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>site</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
                <history>
                    <date type="optime">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                        <hour>11</hour>
                        <minutes>25</minutes>
                        <seconds>59</seconds>
                    </date>
                    <userid>ihcmdm</userid>
                    <type>S</type>
                    <location type="old">
                        <repository>out</repository>
                        <slot>0</slot>
                    </location>
                    <location type="new">
                        <repository>site</repository>
                        <slot>0</slot>
                    </location>
                    <container>0001.kit.000049</container>
                    <date type="movedate">
                        <year>2011</year>
                        <month>04</month>
                        <day>22</day>
                        <dayname>Friday</dayname>
                    </date>
                </history>
            </volume>
            ...

My C# code:

IEnumerable<XElement> caseIdLeavingVault =
    from volume in root.Descendants("volume")
    where
        (from type in volume.Descendants("type")
         where type.Value == "A"
         select type).Any() &&
        (from locationOld in volume.Descendants("location")
         where
             ((String)locationOld.Attribute("type") == "old" &&
              (String)locationOld.Element("repository") == "vault") &&
             (from locationNew in volume.Descendants("location")
              where
                  ((String)locationNew.Attribute("type") == "new" &&
                   (String)locationNew.Element("repository") == "out")
              select locationNew).Any()
         select locationOld).Any()
    select volume.Element("id");

    ...

foreach (XElement volume in caseIdLeavingVault)
{
    Console.WriteLine(volume.Value.ToString());
}

Thanks.

---

OK guys, I'm stumped again. Given this same situation and @Elian's solution below (which works great), I need the "optime" and "movedate" dates for the history used to select the id. Does that make sense? I was hoping to end with something like this:

select new { 
    id = volume.Element("id").Value, 

    // this is from "optime"
    opYear = <whaterver>("year").Value, 
    opMonth = <whatever>("month").Value, 
    opDay = <whatever>("day").Value, 

    // this is from "movedate"
    mvYear = <whaterver>("year").Value, 
    mvMonth = <whatever>("month").Value, 
    mvDay = <whatever>("day").Value 
} 

I have tried so many different combinations, but the Attributes for <date type="optime"> and <date type="movedate"> keep getting in my way and I can't seem to get what I want.

---

OK. I found a solution that works well:

select new {
    caseId = volume.Element("id").Value,

    // this is from "optime"
    opYear = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("year").Value,
    opMonth = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("month").Value,
    opDay = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("day").Value,

    // this is from "movedate"
    mvYear = volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("year").Value,
    mvMonth = volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("month").Value,
    mvDay = volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("day").Value
};

However, it does fail when it finds an id with no "movedate". A few of these exist, so now I am working on that.

---

Well, late yesterday afternoon I finally figured out the solution I had been wanting:

var caseIdLeavingSite =
    from volume in root.Descendants("volume")
    where volume.Elements("history").Any(
        h => h.Element("type").Value == "A" &&
        h.Elements("location").Any(l => l.Attribute("type").Value == "old" && ((l.Element("repository").Value == "site") ||
                                                                               (l.Element("repository").Value == "init"))) &&
        h.Elements("location").Any(l => l.Attribute("type").Value == "new" && l.Element("repository").Value == "toVault")
        )
    select new {
        caseId = volume.Element("id").Value,
        opYear = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("year").Value,
        opMonth = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("month").Value,
        opDay = volume.Descendants("date").Where(t => t.Attribute("type").Value == "optime").First().Element("day").Value,
        mvYear = (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").Any() == true) ? 
                 (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("year").Value) : "0",
        mvMonth = (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").Any() == true) ? 
                  (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("month").Value) : "0",
        mvDay = (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").Any() == true) ? 
                (volume.Descendants("date").Where(t => t.Attribute("type").Value == "movedate").First().Element("day").Value) : "0"
   };

This satisfies the requirements that @Elian helped with and grabs the additional date info necessary. It also accounts for those few instances when there is no element for "movedate" by using the ternary operator ?:.

Now, if anyone knows how to make this more efficient, I'm still interested. Thanks.

I think you want something like this:

IEnumerable<XElement> caseIdLeavingVault =
    from volume in document.Descendants("volume")
    where volume.Elements("history").Any(
        h => h.Element("type").Value == "A" &&
            h.Elements("location").Any(l => l.Attribute("type").Value == "old" && l.Element("repository").Value == "vault") &&
            h.Elements("location").Any(l => l.Attribute("type").Value == "new" && l.Element("repository").Value == "out")
        )
    select volume.Element("id");

Your code independently checks if a volume has a <history> element of type A and a (not necessarily the same) <history> element which has the required <location> elements.

The code above checks if there exists a <history> element that is both of type A and contains the required <location> elements.

Update: Abatishchev suggested a solution that uses an xpath query instead of LINQ to XML, but his query is too simple and doesn't return exactly what you asked for. The following xpath query will do the trick, but it's also a little bit longer:

data/customer/mediatype/volume[history[type = 'A' and location[@type = 'old' and repository = 'vault'] and location[@type = 'new' and repository = 'out']]]/id

Hello SO,

I am somewhat confused about presence of two seemingly identical VB.NET functions: CType(args) and Convert.ToType(args). I'm fairly new to .NET and VB in general, so I'm not quite sure whether one of them is a VB6 legacy or they actually have different purposes / uses / limitations. Is one of the them newer / safer? Are there reasons to use one but not the other?

Cheers! = )

CType is from VB6 times and is not the best when it comes to efficiency. You should be able to use Convert.ToXxxx() methods for convertion and TryCast() and DirectCast() for casting instead of CType().

I'm a newbie in programming and visual basic 2008 language.

I'm learning to use sqlite database in visual basic 2008, and I got the following tutorial code. The code is working correctly and my question is: what is the meaning of that ! mark in the code. Please point to me where to get more information as I wish to learn more about that. I have Windows Sdk v6.1 installed.

Private Sub Button8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
    Dim DatabaseFilepath As String = "e:\sqlite.db3"

    Dim SQLconnect As New System.Data.SQLite.SQLiteConnection()
    Dim SQLcommand As System.Data.SQLite.SQLiteCommand

    SQLconnect.ConnectionString = "Data Source=" & DatabaseFilepath & ";"
    SQLconnect.Open()

    SQLcommand = SQLconnect.CreateCommand

    Dim SchemaTable = SQLconnect.GetSchema(System.Data.SQLite.SQLiteMetaDataCollectionNames.Tables)

    For int As Integer = 0 To SchemaTable.Rows.Count - 1
        If SchemaTable.Rows(int)!TABLE_TYPE.ToString = "table" Then
            MessageBox.Show(SchemaTable.Rows(int)!TABLE_NAME.ToString())
        End If
    Next

    SQLcommand.Dispose()
    SQLconnect.Close()
End Sub

UPDATE:

Can anyone tell me what is the alternative for that bang operator in the code ? That bang operator looks unusual.

Its called the Bang Operator.

It means, use the default property of this type.

VB.NET: Doesn't anyone use the dictionary member access expression? (a.k.a. the bang operator)

I am working on a C# WPF application, using .resx files for resource management. Now, I'm trying to add icons (.ico) to the project but I'm running into some problems.

<Image Name="imgMin" Grid.Column="0"
       Stretch="UniformToFill"
       Cursor="Hand" 
       MouseDown="imgMin_MouseDown">
    <Image.Style>
        <Style TargetType="{x:Type Image}">
            <Setter Property="Source" Value="\Images\minimize_glow.ico"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Source" Value="\Images\minimize_glow.ico"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Image.Style>
</Image>

This works fine, but when I move the icon into AppResources.resx I run into problems with referencing it in the xaml code. What should I be using instead of the Setter Property=... lines above? This:

<Setter Property="Source" Value="{x:Static res:AppResources.minimize}"/>

doesn't work, I think I probably need to use a different Property than "Source" because Value isn't a string pointing to the icon but the icon itself now. I can't figure out which one to use though - some help, please?

The Source property does not "want" a string, it just converts it when it gets one. If you add an icon to the resources it will be of the type System.Drawing.Icon. You will need to convert it to an ImageSource via converter.

You can do a static access to resources but it needs to comply with the expected syntax of x:Static.

e.g.

xmlns:prop="clr-namespace:Test.Properties"

<Image MaxHeight="100" MaxWidth="100">
    <Image.Source>
        <Binding Source="{x:Static prop:Resources.icon}">
            <Binding.Converter>
                <vc:IconToImageSourceConverter/>
            </Binding.Converter>
        </Binding>
    </Image.Source>
</Image>

public class IconToImageSourceConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var icon = value as System.Drawing.Icon;
        var bitmap = icon.ToBitmap();

        //http://stackoverflow.com/questions/94456/load-a-wpf-bitmapimage-from-a-system-drawing-bitmap/1069509#1069509
        MemoryStream ms = new MemoryStream();
        bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
        ms.Position = 0;
        BitmapImage bi = new BitmapImage();
        bi.BeginInit();
        bi.StreamSource = ms;
        bi.EndInit();

        return bi;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

Notes:

• The resource access modifier must be public
• If the image is added as "Image" you end up with a Bitmap instead of an Icon, which requires a different converter