It seems that when a WPF application starts, nothing has focus.
This is really weird. Every other framework I've used does just what you'd expect: puts initial focus on the first control in the tab order. But I've confirmed that it's WPF, not just my app -- if I create a new Window, and just put a TextBox in it, and run the app, the TextBox doesn't have focus until I click on it or press Tab. Yuck.
My actual app is more complicated than just a TextBox. I have several layers of UserControls within UserControls. One of those UserControls has Focusable="True" and KeyDown/KeyUp handlers, and I want it to have the focus as soon as my window opens. I'm still somewhat of a WPF novice, though, and I'm not having much luck figuring out how to do this.
If I start my app and press the Tab key, then focus goes to my focusable control, and it starts working the way I want. But I don't want my users to have to hit Tab before they can start using the window.
I've played around with FocusManager.FocusedElement, but I'm not sure which control to set it on (the top-level Window? the parent that contains the focusable control? the focusable control itself?) or what to set it to.
What do I need to do to get my deeply-nested control to have initial focus as soon as the window opens? Or better yet, to focus the first focusable control in the tab order?
Answer
This works, too:
<Window FocusManager.FocusedElement="{Binding ElementName=SomeElement}">
<DataGrid x:Name="SomeElement">
...
</DataGrid>
</Window>