问题
I'm trying to write an application that responds whenever the Shift key is pressed, no matter what application currently has focus.
I tried this with SetWindowsHookEx() and with GetKeyboardState(), but both of these only work when the application's window has focus. I need it to work globally.
How do I do this?
回答1:
You'll have to use SetWindowsHookEx(). There are only two types of hooks that you can implement in a managed language, WH_KEYBOARD_LL and WH_MOUSE_LL. All other hooks require a DLL that can be injected into another process. Managed DLLs cannot be injected, the CLR cannot be initialized.
This blog post has a functional example.
回答2:
None of the provided answers helped me solve my problem, but I found the answer myself. Here it is.
Using SetWindowsHookEx() with WH_KEYBOARD_LL was the correct approach. However, the other parameters to SetWindowsHookEx() are unintuitive:
- The last parameter,
dwThreadId, needs to be 0. - The second-last parameter,
hMod, needs to point to some DLL. I usedUser32, which is a DLL that is always loaded anyway and is used by all processes with a GUI. I got this idea from a CodeProject post about this.
Thus, the code looks a bit like this:
instance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookFunction, instance, 0);
The documentation is unclear about the second-last parameter. It says:
The hMod parameter must be set to NULL [...] if the hook procedure is within the code associated with the current process.
It doesn't state that this only applies to some types of hooks, but not to WH_KEYBOARD_LL and WH_MOUSE_LL.
回答3:
If you use the technique in the post referenced by nobugz, you will need to make sure the delegate doesn't get garbage-collected, e.g. by using GC.KeepAlive(_proc) when setting the hook, otherwise after an indeterminate period the hook will stop working when the delagate gets GCed.
回答4:
Setup a CBT hook look here http://www.codeproject.com/KB/DLL/keyboardhook.aspx
来源：https://stackoverflow.com/questions/526458/respond-to-keyboard-when-not-in-focus-c-vista