将系统重点放在我的应用上

I have an application that will mainly operate in the background. I want certain system events that it handles to cause the app to steal focus from the foreground app, whatever that is. But UIElement.Focus() seems to only set the focus within the WPF app. That is, if the WPF app already has the focus as a whole, then Focus() sets the focus to the right control. But I need to steal focus from another app and put it on my app. How can I do this?I have an application that will mainly operate