从其他应用程序进入时应用程序没有获得键盘焦点

Question

In WPF I have a Window_KeyDown event which changes the mouse cursor shape when the user presses shift. It works as expected except if I have clicked on another app. So I added a Window_MouseEnter event like this to grab keyboard focus when the mouse reenters my app:

private void Window_MouseEnter(object sender, MouseEventArgs e)
        {
            IInputElement b = Keyboard.Focus(this);
            this.Focus();
            Debug.WriteLine(b + DateTime.Now.ToLongTimeString());
        }

I can see the MouseEnter event firing (with the debug line) when the mouse enters the app but my app still doesn't get keyboard events until I click in the app.

It's irritating because the mouse cursor changes properly when the mouse enters controls within my app so one would expect things to work but the shift-mouse functions don't work until after a click.

What am I missing?

Answer 1

I found that the secret is the Activate() method. I put it in the MouseEnter function which has a side-effect of forcing the entire app to show if some of it was hidden by other apps.

With Activate(), the Focus() method is not needed.