When the user enters a key combination to be used as a hot key, the names of the keys appear in the hot-key control. A key combination can consist of a modifier key (such as CTRL, ALT, or SHIFT) and an accompanying key (such as a character key, an arrow key, a function key, and so on).
After the user has chosen a key combination, the application retrieves the key combination from the hot-key control and uses it to set up a hot key in the system. The information retrieved from the hot-key control includes a flag indicating the modifier key and the virtual-key code of the accompanying key.
The application can use the information provided by a hot-key control to set up a global hot key or a thread-specific hot key. A global hot key is associated with a particular window; it allows the user to activate the window from any part of the system. An application sets a global hot key by using the WM_SETHOTKEY message. Whenever the user uses a global hot key, the window specified in WM_SETHOTKEY receives a WM_SYSCOMMAND message that specifies the SC_HOTKEY value. This message activates the window that receives it. The hot key remains valid until the application that called WM_SETHOTKEY exits.
A thread-specific hot key generates a WM_HOTKEY message that is posted to the beginning of a particular thread so that it is removed by the next iteration of the message loop. An application sets a thread-specific hot key by using the RegisterHotKey function.