Balogh Gergő's List: winhook

• If   nCode is less than zero, the hook procedure must return the value returned by CallNextHookEx.

   

  If nCode is greater than or equal to zero, and the hook procedure did not process the message, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_KEYBOARD_LL hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure processed the message, it may return a nonzero value to prevent the system from passing the message to the rest of the hook chain or the target window procedure.

• An application installs the hook procedure by specifying the WH_KEYBOARD_LL hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.

   

  This hook is called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop.

• The hook procedure should process a message in less time than the data entry specified in the LowLevelHooksTimeout value in the following registry key:  

   

  HKEY_CURRENT_USER\Control Panel\Desktop

   

  The value is in milliseconds. If the hook procedure times out, the system passes the message to the next hook. However, on Windows 7 and later, the hook is silently removed without being called. There is no way for the application to know whether the hook is removed.

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