Creating a Window Inside TThread

Question

im trying to send a message between 2 separate projects, but my problem is that im trying to make the receiver run inside a TThread Object, but WndProc wont work from inside an Object, must be a function, is there anyway to create a window inside a TThread that can process messages inside the thread?

here is what i mean

function TDataThread.WindowProc(hwnd: HWND; uMsg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
 Result := 0;
 case uMsg of
   WM_DATA_AVA: MessageBox(0, 'Data Avaibale', 'Test', 0);
  else Result := DefWindowProc(hwnd, uMsg, wParam, lParam);
 end;
end;

Procedure TDataThread.Create(const Title:String);
begin
 HAppInstance := HInstance;
 with WndClass do
 begin
  Style := 0;
  lpfnWndProc := @WindowProc;          //The Error Lies here (Variable Required)
  cbClsExtra := 0;
  cbWndExtra := 0;
  hInstance := HAppInstance;
  hIcon := 0;
  hCursor := LoadCursor(0, IDC_ARROW);
  hbrBackground := COLOR_WINDOW;
  lpszMenuName := nil;
  lpszClassName := 'TDataForm';
 end;
 Windows.RegisterClass(WndClass);
 MainForm := CreateWindow('TDataForm', PAnsiChar(Title), WS_DLGFRAME , XPos, YPos, 698, 517, 0, 0, hInstance, nil);
end;

i need to have a form so i can get its handle from another application Using FindWindow and FindWindowEx if needed

Answer 1

Running a wndproc in a background thread can be done in Win32, but it's widely regarded as a bad idea.

To do it, you must ensure that your background thread contains a message dispatch loop: GetMessage/TranslateMessage/DispatchMessage. You must ensure that the window handle you want to process messages in the background thread is created on the background thread (CreateWindow is called in the context of the background thread) and all its child windows as well. And you must ensure that your background thread calls its message loop frequently in addition to whatever else it's doing (which kinda defeats the purpose of using a background thread!)

If your background thread doesn't have a message loop, the window handles that are created on the background thread will never receive any messages, so nothing will happen.

Now then, why you shouldn't do this: Windows are message-driven, which means they are inherently a cooperatively multitasked dispatch system. Every GUI windows app has to have a message loop in the main thread to get anything done. That message loop will support virtually any number of windows, all on the main thread. A properly implemented UI will not do anything in the main thread to block execution, so the message loop will always be ready and responsive.

So if the existing message loop on the main thread will handle all your window messaging needs without blocking or freezing, why would you want to make your life more complicated by trying to run a second message loop in a background thread? There is no advantage to using a background thread.