Creating a window inside TThread

Question

im trying to send a message between two separate projects, but my problem is that I am trying to get the receiver to work inside the TThread object, but WndProc does not work from the inside of the object, there must be a function, is there any way to create a window inside TThread that can process messages inside the thread ?

that's 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 that I can get its handle from another application. Use FindWindow and FindWindowEx if necessary.

Answer 1

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

, , : GetMessage/TranslateMessage/DispatchMessage. , , , (CreateWindow ) . , , ( !)

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, : Windows , , . Windows GUI , - . , . , , .

, , , ? .

Answer 2

TThread , TThread , CreateWindow() , . , CreateWindow() TThread Execute(), , :

type
  TDataThread = class(TThread)
  private
    FTitle: String;
    FWnd: HWND;
    FWndClass: WNDCLASS;
    FRegistered: boolean;
    class function WindowProc(hwnd: HWND; uMsg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall; static;
  protected
    procedure Execute; override;
    procedure DoTerminate; override;
  public
    constructor Create(const Title:String); reintroduce;
  end;

constructor TDataThread.Create(const Title: String); 
begin 
  inherited Create(False);
  FTitle := Title;
  with FWndClass do 
  begin 
    Style := 0; 
    lpfnWndProc := @WindowProc;
    cbClsExtra := 0; 
    cbWndExtra := 0; 
    hInstance := HInstance; 
    hIcon := 0; 
    hCursor := LoadCursor(0, IDC_ARROW); 
    hbrBackground := COLOR_WINDOW; 
    lpszMenuName := nil; 
    lpszClassName := 'TDataForm'; 
  end; 
end; 

procedure TDataThread.Execute; 
var
  Msg: TMsg;
begin
  FRegistered := Windows.RegisterClass(FWndClass) <> 0;
  if not FRegistered then Exit;
  FWnd := CreateWindow(FWndClass.lpszClassName, PChar(FTitle), WS_DLGFRAME, XPos, YPos, 698, 517, 0, 0, HInstance, nil); 
  if FWnd = 0 then Exit;
  while GetMessage(Msg, FWnd, 0, 0) > 0 do
  begin
    TranslateMessage(msg);
    DispatchMessage(msg)
  end;
end;

procedure TDataThread.DoTerminate;
begin
  if FWnd <> 0 then DestroyWindow(FWnd);
  if FRegistered then Windows.UnregisterClass(FWndClass.lpszClassName, HInstance);
  inherited;
end;

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 Available', 'Test', 0);
  else
    Result := DefWindowProc(hwnd, uMsg, wParam, lParam);
  end;
end; 

Answer 3

, . ( ) PeekMessage , :

  // Force Message Queue Creation
  PeekMessage(Msg, 0, WM_USER, WM_USER, PM_NOREMOVE);

Loop/Pump , :

  // Run until terminated
  while not Terminated do
  begin

    if GetMessage(@Msg, 0, 0, 0) then
    begin
      case Msg.message of
        WM_DATA_AV: MessageBox(0, 'Data Avaibale', 'Test', 0); 
      else begin
        TranslateMessage(@Msg);
        DispatchMessage(@Msg);
      end;
    end;
  end;

Answer 4

TTestLoopThread = class(TThread)
      private
        FWinHandle: HWND;
        procedure DeallocateHWnd(Wnd: HWND);
      protected
        procedure Execute; override;
        procedure WndProc(var msg: TMessage);
      public
        constructor Create;
        destructor Destroy; override;
      end;

    implementation

    var
      WM_SHUTDOWN_THREADS: Cardinal;

    procedure TForm1.FormCreate(Sender: TObject);
    begin
      WM_SHUTDOWN_THREADS := RegisterWindowMessage('TVS_Threads');
    end;

    procedure TForm1.Button1Click(Sender: TObject);
    begin
      TTestLoopThread.Create;
    end;

    procedure TForm1.Button2Click(Sender: TObject);
    begin
      SendMessage(wnd_broadcast, WM_SHUTDOWN_THREADS, 0, 0);
    end;

    { TTestLoopThread }

    constructor TTestLoopThread.Create;
    begin
      inherited Create(False);
    end;

    destructor TTestLoopThread.Destroy;
    begin
      inherited;
    end;

    procedure TTestLoopThread.DeallocateHWnd(Wnd: HWND);
    var
      Instance: Pointer;
    begin
      Instance := Pointer(GetWindowLong(Wnd, GWL_WNDPROC));
      if Instance <> @DefWindowProc then
        // make sure we restore the old, original windows procedure before leaving
        SetWindowLong(Wnd, GWL_WNDPROC, Longint(@DefWindowProc));
      FreeObjectInstance(Instance);
      DestroyWindow(Wnd);
    end;

    procedure TTestLoopThread.Execute;
    var
      Msg: TMsg;
    begin
      FreeOnTerminate := True;
      FWinHandle := AllocateHWND(WndProc); //Inside Thread
      try
      while GetMessage(Msg, 0, 0, 0) do
        begin
         TranslateMessage(Msg);
         DispatchMessage(Msg);
        end;
      finally
      DeallocateHWND(FWinHandle);
      end;
    end;

    procedure TTestLoopThread.WndProc(var msg: TMessage);
    begin
      if Msg.Msg = WM_SHUTDOWN_THREADS then
      begin
       Form1.Memo1.Lines.Add('Thread ' + IntToStr(ThreadID) + ' shutting down.');
       PostMessage(FWinHandle, WM_QUIT, 0, 0);
      end
      else
       Msg.Result := DefWindowProc(FWinHandle, Msg.Msg, Msg.wParam, Msg.lParam);
    end;