在.NET中，我可以检测系统焦点事件（C＃）吗？

Is it possible to determine when window focus changes at the system level? I'm writing a time-tracking application, and I'd like to be able to listen for application switching (so that I can begin logging time in a given application). I've poked around the Process class for a good hour here, and while I learned quite a few useful things, I didn't find what I was looking for. I suspect I'll need to use hooks, but it's difficult finding clear documentation on the process, let alone documentation specific to what I'm asking.Is it possible to determine when window focus c