Question

I usually use Dispatcher.Invoke when i need to access some UI elements from background thread. Recently i had to change other’s written sources and i saw that same tasks he accomplishes with constructions like:

Dispatcher.Invoke((ThreadStart)delegate
            {
              //some code that uses controls from UI
            });

When should i use such code instead of Dispatcher.Invoke/BeginInvoke and why?

Answer 1

That does use Dispatcher.Invoke – it’s not an “instead of”. That code is just using ThreadStart as a way of telling the compiler the delegate type to convert the anonymous method to.

It’s equivalent to:

ThreadStart tmp = delegate
{
    // Code
};
Dispatcher.Invoke(tmp);

Personally I’d use Action instead of ThreadStart here as you’re not actually starting a thread, but it’s a pretty arbitrary choice. Ignore the fact that it’s called ThreadStart – it’s just a delegate with a void return type and no parameters.

EDIT: The reason you have to specify a delegate type is that the compiler can’t convert an anonymous function (i.e. an anonymous method or a lambda expression) to just Delegate, which is the argument type of Dispatcher.Invoke.

One workaround for this is to write an extension method:

public static void InvokeAction(this Dispatcher dispatcher, Action action)
{
    dispatcher.Invoke(action);
}

You can then use:

foo.Dispatcher.InvokeAction(() => { /* stuff */ });

and the compiler knows to convert the lambda expression to Action.