Use Windows Hooks in Delphi Applications

Code submitted by Jens Borrisholt. Text by Zarko Gajic. By Jens: Hooks, I’ve seen a lot of people trying to make a clean solution for hooking messages in an application. So I decided some time ago to implement hooks as a class, with nice events and stuff :) Hook.pas makes it possible to assign a method pointer to a procedure pointer (with some help from assembler). For example: if you want to trap ALL keystrokes in your application - simply declare an instance of TKeyboardHook, assign an event handler for OnPreExecute or OnPostExecute, or both. Set you KeyboadHook active (KeyboardHook.Active : True) and you are out and running .. On Windows Hooks A hook is a point in the system message-handling mechanism where an application can install a subroutine to monitor the message traffic in the system and process certain types of messages before they reach the target window procedure. Put shortly, a hook is a function you can create as part of a dll or your application to monitor the goings on inside the Windows operating system. The idea is to write a function that is called every time a certain event in windows occurs - for example when a user presses a key on the keyboard or moves the mouse. For a more in depth introduction to hooks, take a look at What Windows hooks are and how to use them within a Delphi application. Hooking mechanism relies on Windows messages and callback functions. Types of Hooks For example:You can use the WH_KEYBOARD hook to monitor keyboard input posted to a message queue;You can use the WH_MOUSE hook to monitor mouse input posted to a message queue;You can a WH_SHELL hook procedure when the shell application is about to be activated and when a top-level window is created or destroyed. Hooks.pas TCBTHook - called before activating, creating, destroying, minimizing, maximizing, moving, or sizing a window; before completing a system command; before removing a mouse or keyboard event from the system message queue; before setting the input focus; or before synchronizing with the system message queue.TDebugHook - called before calling hook procedures associated with any other hook in the systemTGetMessageHook - enables an application to monitor messages about to be returned by the GetMessage or PeekMessage functionTJournalPlaybackHook - enables an application to insert messages into the system message queue.TJournalRecordHook - enables you to monitor and record input events (to record a sequence of mouse and keyboard events to play back later by using the WH_JOURNALPLAYBACK Hook).TKeyboardHook - enables an application to monitor message traffic for WM_KEYDOWN and WM_KEYUP messages.TMouseHook - enables you to monitor mouse messages about to be returned by the GetMessage or PeekMes sage function.TLowLevelKeyboardHook - enables you to monitor keyboard input events about to be posted in a thread input queue.TLowLevelMouseHook - enables you to monitor mouse input events about to be posted in a thread input queue. TKeyboardHook example Download hooks.pas demo application uses hooks, .... var   Ã‚  KeyboardHook: TKeyboardHook; .... //MainForms OnCreate event handlerprocedure TMainForm.FormCreate(Sender: TObject) ; begin   Ã‚  KeyboardHook : TKeyboardHook.Create;   Ã‚  KeyboardHook.OnPreExecute : KeyboardHookPREExecute;   Ã‚  KeyboardHook.Active : True; end; //handles KeyboardHooks OnPREExecuteprocedure TMainForm.KeyboardHookPREExecute(Hook: THook; var Hookmsg: THookMsg) ; var   Ã‚  Key: Word; begin   Ã‚  //Here you can choose if you want to return   Ã‚  //the key stroke to the application or not   Ã‚  Hookmsg.Result : IfThen(cbEatKeyStrokes.Checked, 1, 0) ;   Ã‚  Key : Hookmsg.WPARAM;   Ã‚  Caption : Char(key) ; end; Ready, set, hook :)