When you write a WPF app and start it up, nothing has focus.
I’d call this a bug, but Microsoft has scads of testers. Somebody had to have noticed. So I can only conclude that somebody decided, on purpose, that when you write a WPF app and run it, the user shouldn’t be able to just start typing.
This is completely unlike the other two major GUI frameworks I’ve used (Delphi VCL and Windows Forms), where the app is usable by default: you open a window, your focus is in the first control in the tab order. I was therefore rather grumpy when I found out about the WPF brokenness.
Fortunately, after some digging around in Reflector, I found a nice, general fix. Adding this to the window’s constructor:
Loaded += (sender, e) => MoveFocus(new TraversalRequest(FocusNavigationDirection.Next));
will re-enable the standard behavior: initial focus is in the first control in the tab order.
This line could easily be pulled into a base class, so that all your windows can automatically inherit this behavior.