Anonymous method in Invoke call

Question

Because Invoke/BeginInvoke accepts Delegate (rather than a typed delegate), you need to tell the compiler what type of delegate to create ; MethodInvoker (2.0) or Action (3.5) are common choices (note they have the same signature); like so:

control.Invoke((MethodInvoker) delegate {this.Text = "Hi";});

If you need to pass in parameters, then "captured variables" are the way:

string message = "Hi";
control.Invoke((MethodInvoker) delegate {this.Text = message;});

(caveat: you need to be a bit cautious if using captures async, but sync is fine - i.e. the above is fine)

Another option is to write an extension method:

public static void Invoke(this Control control, Action action)
{
    control.Invoke((Delegate)action);
}

then:

this.Invoke(delegate { this.Text = "hi"; });
// or since we are using C# 3.0
this.Invoke(() => { this.Text = "hi"; });

You can of course do the same with BeginInvoke:

public static void BeginInvoke(this Control control, Action action)
{
    control.BeginInvoke((Delegate)action);
}

If you can't use C# 3.0, you could do the same with a regular instance method, presumably in a Form base-class.

Actually you do not need to use delegate keyword. Just pass lambda as parameter:

control.Invoke((MethodInvoker)(() => {this.Text = "Hi"; }));

myControl.Invoke(new MethodInvoker(delegate() {...}))

You need to create a delegate type. The keyword 'delegate' in the anonymous method creation is a bit misleading. You are not creating an anonymous delegate but an anonymous method. The method you created can be used in a delegate. Like this:

myControl.Invoke(new MethodInvoker(delegate() { (MyMethod(this, new MyEventArgs(someParameter)); }));

For the sake of completeness, this can also be accomplished via an Action method/anonymous method combination:

//Process is a method, invoked as a method group
Dispatcher.Current.BeginInvoke((Action) Process);
//or use an anonymous method
Dispatcher.Current.BeginInvoke((Action)delegate => {
  SomeFunc();
  SomeOtherFunc();
});

I had problems with the other suggestions because I want to sometimes return values from my methods. If you try to use MethodInvoker with return values it doesn't seem to like it. So the solution I use is like this (very happy to hear a way to make this more succinct - I'm using c#.net 2.0):

    // Create delegates for the different return types needed.
    private delegate void VoidDelegate();
    private delegate Boolean ReturnBooleanDelegate();
    private delegate Hashtable ReturnHashtableDelegate();

    // Now use the delegates and the delegate() keyword to create 
    // an anonymous method as required

    // Here a case where there's no value returned:
    public void SetTitle(string title)
    {
        myWindow.Invoke(new VoidDelegate(delegate()
        {
            myWindow.Text = title;
        }));
    }

    // Here's an example of a value being returned
    public Hashtable CurrentlyLoadedDocs()
    {
        return (Hashtable)myWindow.Invoke(new ReturnHashtableDelegate(delegate()
        {
            return myWindow.CurrentlyLoadedDocs;
        }));
    }

I like to use Action in place of MethodInvoker, it is shorter and looks cleaner.

Invoke((Action)(() => {
    DoSomething();
}));

// OR

Invoke((Action)delegate {
    DoSomething();
});

Eg.

// Thread-safe update on a form control
public void DisplayResult(string text){
    if (txtResult.InvokeRequired){
        txtResult.Invoke((Action)delegate {
            DisplayResult(text);
        });
        return;
    }

    txtResult.Text += text + "\r\n";
}