Question

I have this delegate:

private delegate void NoArgDelegate(BitmapImage image);

I instantiate the delegate and run it with Dispatcher.Invoke like so:

var fetcher =  new NoArgDelegate(InstantiateForm);
Dispatcher.Invoke(fetcher, DispatcherPriority.Normal, imageToPassIn);

I have a private field outside of the scope of any method but inside the scope of my ViewModel, inside InstantiateForm I instantiate the object:

private OmrForm _ormForm;

private void InstantiateForm(BitmapImage image)
{
    _ormForm = new OmrForm(image);
}

This is all happening in a method inside my ViewModel which runs on the click event of the button on my WPF form.

I do some work in the constructor to work out what type of image I have passed in and set coordinates appropriately, this about 2 seconds, and I want my UI to be responsive during this time, but it’s not. I have tried using BeginInvoke also to no avail.

What is going on here, why isn’t my method being run asynchronously?

Answer 1

Calling Dispatcher.Invoke inside a Window or UserControl will run that code on the UI thread, since the Dispatcher of a control is set to work on the UI thread.

What you want is to start a background thread. This can be achieved using the Task class.

Task.Factory.StartNew(() => InstantiateForm(imageToPassIn));