The Hook Code is depending on the type of the Hook.įor each Hook type, there may be some additional details to be passed and these details are available through the rest of the arguments in the HookProc callback function. Where hook_code is the Hook Code, Hook Procedure will use to determine the action to perform. LRESULT CALLBACK HookProc( int hook_code, WPARAM message_info_1, LPARAM message_info_2 ) Windows will call this function, whenever there is a related message generated in the System. The Syntax of the Hook Procedure is looks like below: This is the callback function. The Application must implement the Hook Procedure in order to process the messages relevant to the registered Hook Types. Upon success, this Win32 API function returns the handle to the Hook. Thread_id is the Thread to which the Hook Procedure is associated. Hook Procedure can be placed in a separate DLL or into the same Application from where calling this Win32 API function. Module_handle is the handle to the module where the Hook Procedure is placed. Lpfn is the pointer to the Hook Procedure this is application specific call back function. For example, to monitor Keyboard message Windows WH_KEYBOARD (Value 2) hook type will be used to monitor Mouse messages, it is WH_MOUSE (Value 7) hook type etc. Where hook_proc_type is the type of the Hook Procedure to be installed in the Hook Chain. HHOOK SetWindowsHookEx(int hook_proc_type, HOOKPROC lpfn, HINSTANCE module_handle, DWORD thread_id) The Syntax of this function looks like below: SetWindowsHookEx Win32 API function will register or install the Hook Procedure into the Hook Chain. This is possible through calling the Win32 API function SetWindowsHookEx. We must have to tell to Windows to execute our Procedure (called Hook Procedure) instead of Windows Procedure when an Event occurred or Message is generated. In another words, when the Applications are registering the Hook Procedures, Windows will maintain a Hook Chain to allow to all the Applications to give a chance to run their Application specific procedures (Hook Procedures) when an event occurred. Hook Chain is nothing but a list of pointers to point to the Hook Procedures and Windows will maintain a separate Hook Chain for each type of Hook. Installing a Hook Procedureįirst thing we need in our Application, to receive the messages (even though the Application is in-active) is to install the Hook Procedure in the Hook Chain. Hook Procedures are call back functions.ĭoes it possible to place our function in the message handling mechanism to execute whenever a particular event occurred? Yes, below section explains this. Hook is an entry in the message handling mechanism will execute a procedure, which is called the Hook Procedure, before executing the relevant Windows Procedure(s) for the particular message(s). How about receiving all the events whichever generated? This is where Windows Hooks comes into the picture. There are different types of messages Windows will generate to do particular Actions.When the Application is active, relevant messages will be routed to the active Application. A Windows Procedure or the Application specific Procedure will process the message. There is a message handling mechanism in the Windows to handle or process the messages.įor example, when the User press the key from the Keyboard relevant message will be generated and will process through message handling mechanism. Windows Procedures or Application methods are going to execute whenever there is an event occurred. If (PeekMessage(out msg, IntPtr.Windows Applications are message or event driven applications. Private static void WindowEventCallback(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNPROCESS) Public static void SubscribeToWindowEvents() Public static WinEventProc _winEventProc = new WinEventProc(WindowEventCallback) UserWatchdog userWatchdog = new UserWatchdog() My code looks like this: protected override void OnStart(string args) Everything seems fine except the fact that I am not receiving anything in the callback method passed to SetWinEventHook. To do this I made a Window Service type of project, created a service installer in it, and OnStart method from the template service project I registered to events using SetWinEventHook from user32.dll. I am trying to develop an application that will hook to windows events and notify me when for eg.
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