Delegate with optional parameter throws runtime exception

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I have code like this:

C#

private delegate string MyDelegate(int requiredParameter, int optionalParameter = -1);
private string MyMethod(int requiredParameter, int optionalParameter = -1)
{
    return "Some return value";
}

Which I then call like this:

C#

string s = (string)this.Invoke(new MyDelegate(MyMethod), new object[] { 10 });

Based on some questions I saw on StackOverflow, I think that what I'm trying to do is possible, but this last line throws a TargetParameterCountException with the message Parameter count mismatch.

Any idea why this happens? Can I make it work in some manner that is more elegant than overloading?

Posted 18-Apr-12 22:16pm

BotCar

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parul77 · Answer 1 · 2012-04-18T22:31:00

Solution 1

please refer once:
http://stackoverflow.com/questions/2484226/invoking-eventhandler-generic-targetparametercountexception[^]

Posted 18-Apr-12 22:31pm

parul77

Comments

BotCar 19-Apr-12 4:53am

This works fine, up to the point of invoking the delegate. Unfortunately, Invoke now returns null.

Mehdi Gholam · Answer 2 · 2012-04-18T22:40:00

Solution 2

If you know which method you are calling then

C#

string s = (string)this.Invoke(new MyDelegate(MyMethod), new object[] { 10 });

is pointless just do

C#

string s = MyMethod(10);

However if your method is dynamic then it would be set somewhere like

C#

private MyDelegate _mydelegate;

public void SetDelegate(MyDelegate del)
{
   _mydelegate = del;
}

and you would call this by

C#

private void somemethod()
{
     string s = _del(10); //using the defined delegate
}

Posted 18-Apr-12 22:40pm

Mehdi Gholam

Comments

BotCar 19-Apr-12 4:55am

It is done for thread safety. It is basically a way to force the method to be executed on the GUI thread.

Mehdi Gholam 19-Apr-12 5:05am

Delegates are so you don't have to do this kind of reflection, and they are thread safe.

BotCar 19-Apr-12 5:32am

Not true. As soon as I try executing the delegate without invoking it on the appropriate control, I get an InvalidOperationException telling me the cross-thread operation is not valid because the control can only be accessed from the thread it was created on.

Mehdi Gholam 19-Apr-12 9:16am

You are probably updating UI controls in your delegate, and not doing computations.

BotCar 19-Apr-12 9:27am

Yes. That's why I invoke the method on the UI thread.