Question

I’m using the following code in my WPF Project :

Task.Factory.StartNew(
                        () =>
                        {
                            if (Keyboard.Modifiers == ModifierKeys.Alt) // <- Here
                                Thread.Sleep(1000);                            
                        })
                        .ContinueWith(t =>
                        {
                          // do somthing
                        });

and i’ll get the InvalidOperationException on :

if (Keyboard.Modifiers == ModifierKeys.Alt)

and it tells me :

The calling thread must be STA, because many UI components require
this.

I just don’t get it !! It seems to be a simple code, but why ?

Answer 1

You need to go onto the UI thread to get access to the Keyboard. Try this:

                Task.Factory.StartNew(
                        () =>
                        {
                            if ((bool)Dispatcher.Invoke(DispatcherPriority.Normal, new Func<bool>(() =>
                            {
                                 return Keyboard.Modifiers == ModifierKeys.Alt;
                             })))
                             {
                                Thread.Sleep(1000);                            
                             }
                        })
                        .ContinueWith(t =>
                        {
                          // do somthing
                        });