Author: Jonas Bilinkevicius

How to catch windows keystrokes and pass them to an assigned event

Answer:

For those interested, here's a keyboard hook component that catches windows 
keystrokes and passes them to an assigned event.

1   unit KeyboardHook;
2   {
3     By William Egge
4     Sep 20, 2002
5     egge@eggcentric.com
6     http://www.eggcentric.com
7   
8     This code may be used/modified however you wish.
9   }
10  
11  interface
12  
13  uses
14    Windows, Classes;
15  
16  type
17    TCallbackThunk = packed record
18      POPEDX: Byte;
19      MOVEAX: Byte;
20      SelfPtr: Pointer;
21      PUSHEAX: Byte;
22      PUSHEDX: Byte;
23      JMP: Byte;
24      JmpOffset: Integer;
25    end;
26  
27    {See windows help on KeyboardProc or press F1 while your cursor is on 
28  "KeyboardProc"}
29    TKeyboardCallback = procedure(code: Integer; wparam: WPARAM; lparam: LPARAM) of
30      object;
31  
32    TKeyboardHook = class(TComponent)
33    private
34      { Private declarations }
35      FHook: HHook;
36      FThunk: TCallbackThunk;
37      FOnCallback: TKeyboardCallBack;
38      function CallBack(code: Integer; wparam: WPARAM; lparam: LPARAM): LRESULT 
39  stdcall;
40      procedure SetOnCallback(const Value: TKeyboardCallBack);
41    protected
42      { Protected declarations }
43    public
44      { Public declarations }
45      constructor Create(AOwner: TComponent); override;
46      destructor Destroy; override;
47    published
48      { Published declarations }
49      property OnCallback: TKeyboardCallBack read FOnCallback write SetOnCallback;
50    end;
51  
52  procedure register;
53  
54  implementation
55  
56  procedure register;
57  begin
58    RegisterComponents('EggMisc', [TKeyboardHook]);
59  end;
60  
61  { TKeyboardHook }
62  
63  function TKeyboardHook.CallBack(code: Integer; wparam: WPARAM; lparam: LPARAM):
64    LRESULT;
65  begin
66    if Code < 0 then
67      Result := CallNextHookEx(FHook, Code, wparam, lparam)
68    else
69    begin
70      if Assigned(FOnCallback) then
71        FOnCallback(Code, wParam, lParam);
72      Result := 0;
73    end;
74  end;
75  
76  constructor TKeyboardHook.Create(AOwner: TComponent);
77  begin
78    inherited Create(AOwner);
79    FThunk.POPEDX := $5A;
80    FThunk.MOVEAX := $B8;
81    FThunk.SelfPtr := Self;
82    FThunk.PUSHEAX := $50;
83    FThunk.PUSHEDX := $52;
84    FThunk.JMP := $E9;
85    FThunk.JmpOffset := Integer(@TKeyboardHook.Callback) - Integer(@FThunk.JMP) - 5;
86    FHook := SetWindowsHookEx(WH_KEYBOARD, TFNHookProc(@FThunk), 0, MainThreadID);
87  end;
88  
89  destructor TKeyboardHook.Destroy;
90  begin
91    UnhookWindowsHookEx(FHook);
92    inherited;
93  end;
94  
95  procedure TKeyboardHook.SetOnCallback(const Value: TKeyboardCallBack);
96  begin
97    FOnCallback := Value;
98  end;
99  
100 end.