在捕获鼠标但窗口未聚焦的同时捕获键盘事件（Win32）

Question

I'm implementing a custom control that can initiate drag events. I initiate a drag when the user presses the left mouse button by processing WM_LBUTTONDOWN and calling SetCapture() . This causes all mouse events, even those outside my control's client area, to be sent to it, exactly as I want.

I would also like to be able to capture key presses so I can cancel the drag if the user presses the ESC key ( VK_ESCAPE ). Since my control doesn't have the keyboard focus (and I don't want it to steal the focus away from the control that has it), I can't listen to WM_KEYDOWN . For other reasons too complicated to explain, I also would prefer not to use the DragDetect() function.

How can my control find out about ESC key presses while the drag is ongoing?

Answer 1

It turns out it's this easy:

// message loop...
switch (msg)
{
    // ...

    case WM_LBUTTONDOWN:
        // do some stuff
        RegisterHotKey(hwnd, 0 /* id */, 0, VK_ESCAPE);
        // do some more stuff
        break;

    // ... 

    case WM_HOTKEY:
        if (VK_ESCAPE == HIWORD(lParam) &&
            IDHOT_SNAPDESKTOP != wParam &&
            IDHOT_SNAPWINDOW != wParam)
            {
            // handle ESC keypress
            UnregisterHotKey(hwnd, 0 /* id */);
            }
        break;

    // ...

}