Cross-thread operation not valid using async/await in VSTO

Question

I am getting a

Cross-thread operation not valid

... error with the code below. I thought async/await would take care this, but apparently not. Weird thing is that when I comment out textBoxUser.Enabled = false , the error disappears. Thoughts?

private async void buttonPopulate_Click(object sender, EventArgs e)
{
     textBoxUser.Enabled = false;

     await Populate(); 

     textBoxUser.Enabled = true; //error here
}

Answer 1

Your problem is probably due to VSTO not properly providing a SynchronizationContext ; this is a long-standing problem with Office plugin systems. You can verify this by checking the value of SynchronizationContext.Current at the beginning of your event handler; if it is null , then the problem is due to VSTO.

To fix this, you can do this at the beginning of any async void event handlers:

SynchronizationContext.SetSynchronizationContext(new WindowsFormsSynchronizationContext());