Adding a system-wide keyboard hook to your WPF Application

A global keyboard hook is, as the name suggests, a means for your application to intercept (or ‘hook’) all keyboard events, not just those that occur when your application has focus. Recently I needed just such a keyboard hook for a WPF application, and wanted to be able to set focus back to my application when a particular keyboard combination was pressed. Using the C# keyboard hooking code of Stephen Toub as a starting point I created the desired system keyboard hook for WPF.

I’ve added the code to my learnwpf.com samples project on bitbucket. The key moving parts are:

keyboardhook.cs – This contains the Win32 API calls for hooking keyboard input, as well as a static method for bringing focus back to a window of your choice when the keyboard hook is triggered (which is surprisingly hard in more modern versions of windows where some measures have been taken to stop apps stealing focus from others.) This code also uses the Keyboard.Modifiers to check to see if the CTRL key has been pressed. There were some posts on-line that suggested that this doesn’t work properly when your app doesn’t have focus (which would be a major problem for what we’re doing). Fortunately it seems that this problem has been solved in .NET 4.0.

Read more: LearnWP3
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