Author: Tomas Rutkauskas

I have a (separate) thread that spends most of its time waiting for 
(synchronisation) events, and when an event occurs it performs some processing 
which involves user-specific (Delphi) event handling. In these event handlers I 
would now like to be able to create objects that uses Windows messages, such as 
TTimers or some other own-developed components we have, and that these objects 
should be able to generate (Delphi) events as they normally would (although 
executed in my separate thread, of course).

Answer:

I usually use messages within threads and works fine, I attach 2 procedures that 
allows you to create/ free a window handle inside a TThread object and to use the 
standard Delphi way to handle messages. The function are:

CreateWindowHandle(AObject: TObject): integer;
FreeWindowHandle(AHandle: integer);

You should use them in the following way:

1   { ... }
2   type
3     TMyThread = class(TThread)
4     private
5       hwnd: integer;
6     protected
7       procedure handler1(var message: TMessage); message WM_USER; {or any other 
8   message}
9     end;
10  
11  constructor Create { ... }
12  begin
13    { ... }
14    hwnd := CreateWindowHandle(Self);
15    { ... }
16  end;
17  
18  destructor Destroy { ... }
19  begin
20    { ... }
21    freewindowhandle(hwnd);
22    { ... }
23  end;
24  
25  var
26    ObjectWindowClass: TWndClass = (style: 0; lpfnWndProc: @windows.DefWindowProc;
27      cbClsExtra: 0; cbWndExtra: 0; hInstance: 0; hIcon: 0;
28      hCursor: 0; hbrBackground: 0; lpszMenuName: nil;
29      lpszClassName: 'ObjectWindowClass@wbuwbvubvy');
30  
31  function ObjectWindowProc(HWnd, Msg, wParam, lParam: integer): integer; stdcall;
32  var
33    m: TMessage;
34  begin
35    m.Msg := uint(msg);
36    m.wParam := wParam;
37    m.lParam := lParam;
38    TObject(GetWindowLong(hwnd, GWL_USERDATA)).Dispatch(m);
39    result := m.Result;
40  end;
41  
42  function CreateWindowHandle(AObject: TObject): integer;
43  var
44    TempClass: TWndClass;
45    ClReg: Boolean;
46    hwnd: integer;
47  begin
48    {register the window class (if not already registered) }
49    ObjectWindowClass.hInstance := HInstance;
50    ClReg := GetClassInfo(HInstance, ObjectWindowClass.lpszClassName, TempClass);
51    if (not ClReg) or (TempClass.lpfnWndProc <> @windows.DefWindowProc) then
52    begin
53      if ClReg then
54        Windows.UnregisterClass(ObjectWindowClass.lpszClassName, HInstance);
55      Windows.RegisterClass(ObjectWindowClass);
56    end;
57    {create the window}
58    HWnd := CreateWindow(ObjectWindowClass.lpszClassName, '', 0, 0, 0, 0, 0, 0, 0,
59      HInstance, nil);
60    {subclass the window}
61    SetWindowLong(HWnd, GWL_USERDATA, integer(AObject));
62    SetWindowLong(HWnd, GWL_WNDPROC, integer(@ObjectWindowProc));
63    Result := HWnd;
64  end;
65  
66  procedure FreeWindowHandle(AHandle: integer);
67  begin
68    SetWindowLong(AHandle, GWL_WNDPROC, integer(@windows.DefWindowProc));
69    DestroyWindow(AHandle);
70  end;