Why doesn’t QWinHost draw, when it has a parent?

[korel]

I’m using QWinMigrate library to draw something MFC on Qt widgets.
When I create HostWindow (subclass QWinHost) independently – all is fine!
But When I set a parent to HostWindow (Qt QMainWindow – in my case) only black rectangle appear instead … Please, tell what’s wrong I do.
Considered examples on http://doc.trolltech.com/solutions/q...t-example.html

I have written code bellow:
————-Declaration————-

class HostWindow : public QWinHost
  {
  Q_OBJECT
 
  private:
    static CWnd* mp_wnd;
 
  public:
    HostWindow(QWidget* ip_parent = 0, Qt::WFlags f = 0);
    ~HostWindow();
 
    HWND createWindow(HWND i_parent, HINSTANCE i_instance);
 
  protected:
    static LRESULT CALLBACK WndProc(HWND i_hWnd, UINT i_message, WPARAM i_wParam, LPARAM i_lParam);
  };

class HostWindow : public QWinHost
  {
  Q_OBJECT
   
  private:
    static CWnd* mp_wnd;
 
  public:
    HostWindow(QWidget* ip_parent = 0, Qt::WFlags f = 0);
    ~HostWindow();
 
    HWND createWindow(HWND i_parent, HINSTANCE i_instance);
 
  protected:
    static LRESULT CALLBACK WndProc(HWND i_hWnd, UINT i_message, WPARAM i_wParam, LPARAM i_lParam);
  };

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///////////////////////////////////////
————-Definition—————-

CWnd* HostWindow::mp_wnd = 0;
 
HostWindow::HostWindow(QWidget* ip_parent, Qt::WFlags f) : QWinHost(ip_parent, f)
  {}
 
HostWindow::~HostWindow()
  {}
 
HWND HostWindow::createWindow(HWND i_parent, HINSTANCE i_instance)//todo check for if needless
  {
   static ATOM windowClass = 0;
  if ( !windowClass ) {
    WNDCLASSEX wcex;
    wcex.cbSize         = sizeof(WNDCLASSEX);
    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = (WNDPROC)WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = i_instance;
    wcex.hIcon          = NULL;
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = NULL;
    wcex.lpszClassName  = L"qtest";
    wcex.hIconSm        = NULL;
 
    windowClass = RegisterClassEx(&wcex);
    }
 
  HWND hwnd = CreateWindow((TCHAR*)windowClass, 0, WS_CHILD | WS_VISIBLE,
                CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, i_parent, NULL, i_instance, NULL);
 
 
  mp_wnd = new CWnd;
  mp_wnd->SubclassWindow(hwnd);
  return mp_wnd->GetSafeHwnd();
  }
 
 
LRESULT CALLBACK HostWindow::WndProc(HWND i_hWnd, UINT i_message, WPARAM i_wParam, LPARAM i_lParam)
  {
  QWidget *widget = QWidget::find(GetParent(i_hWnd));
  HostWindow *window = NULL;
  if(widget->inherits("HostWindow"))
    window = (HostWindow*)widget;
 
  if(window)
    {
    switch (i_message) 
      {
      case WM_PAINT:
        {
        qDebug()<<"WM_PAINT\n";
/////////////////////////////////////
        CRect rect;
        mp_wnd->GetClientRect(rect);
        CDC* c_dc = CDC::FromHandle(GetDC(mp_wnd->GetSafeHwnd()));
        CBrush brush;
       brush.CreateSolidBrush(RGB(255,0,0));
       CBrush *pOldBrush= c_dc->SelectObject(&brush);
       c_dc->Ellipse(rect);
       c_dc->SelectObject(pOldBrush);
 
/////////////////////////////////////
        }
        break;
      default:
        return DefWindowProc(i_hWnd, i_message, i_wParam, i_lParam);
      }
    }
    return 0;
  }
 
 
class MainWindow : public QMainWindow
{
//..
   HostWindow* mp_host_window;
//..
}
 
MainWindow::MainWindow(QWidget *parent, Qt::WFlags flags): QMainWindow(parent, flags)
  {
 //... doesn't work (reproduces a black rect area)
 
 mp_host_window = new HostWindow(this);
 
 //..
 
 //.. shows separated window with right drawed ellipse
 
 mp_host_window = new HostWindow;
 mp_host_window->show()
 
 //..
  }

CWnd* HostWindow::mp_wnd = 0;
 
HostWindow::HostWindow(QWidget* ip_parent, Qt::WFlags f) : QWinHost(ip_parent, f)
  {}
 
HostWindow::~HostWindow()
  {}
 
HWND HostWindow::createWindow(HWND i_parent, HINSTANCE i_instance)//todo check for if needless
  {
   static ATOM windowClass = 0;
  if ( !windowClass ) {
    WNDCLASSEX wcex;
    wcex.cbSize         = sizeof(WNDCLASSEX);
    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = (WNDPROC)WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = i_instance;
    wcex.hIcon          = NULL;
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = NULL;
    wcex.lpszClassName  = L"qtest";
    wcex.hIconSm        = NULL;
 
    windowClass = RegisterClassEx(&wcex);
    }
 
  HWND hwnd = CreateWindow((TCHAR*)windowClass, 0, WS_CHILD | WS_VISIBLE,
                CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, i_parent, NULL, i_instance, NULL);
 
 
  mp_wnd = new CWnd;
  mp_wnd->SubclassWindow(hwnd);
  return mp_wnd->GetSafeHwnd();
  }
 
 
LRESULT CALLBACK HostWindow::WndProc(HWND i_hWnd, UINT i_message, WPARAM i_wParam, LPARAM i_lParam)
  {
  QWidget *widget = QWidget::find(GetParent(i_hWnd));
  HostWindow *window = NULL;
  if(widget->inherits("HostWindow"))
    window = (HostWindow*)widget;
 
  if(window)
    {
    switch (i_message) 
      {
      case WM_PAINT:
        {
        qDebug()<<"WM_PAINT\n";
/////////////////////////////////////
        CRect rect;
        mp_wnd->GetClientRect(rect);
        CDC* c_dc = CDC::FromHandle(GetDC(mp_wnd->GetSafeHwnd()));
        CBrush brush;
       brush.CreateSolidBrush(RGB(255,0,0));
       CBrush *pOldBrush= c_dc->SelectObject(&brush);
       c_dc->Ellipse(rect);
       c_dc->SelectObject(pOldBrush);
 
/////////////////////////////////////
        }
        break;
      default:
        return DefWindowProc(i_hWnd, i_message, i_wParam, i_lParam);
      }
    }
    return 0;
  }
 
 
class MainWindow : public QMainWindow
{
//..
   HostWindow* mp_host_window;
//..
}
 
MainWindow::MainWindow(QWidget *parent, Qt::WFlags flags): QMainWindow(parent, flags)
  {
 //... doesn't work (reproduces a black rect area)
 
 mp_host_window = new HostWindow(this);
  
 //..
 
 //.. shows separated window with right drawed ellipse
 
 mp_host_window = new HostWindow;
 mp_host_window->show()
  
 //..
  }

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[changbiyuan]

I realize this post is rather stale, but in the interest of future reference, I think I had the same problem you're having when I started using QWinHost. I fixed it by overriding focusInEvent() to make sure the Win32 window would redraw when it needed to:

void HostWindow::resizeEvent(QResizeEvent* e)
{
   QWinHost::resizeEvent(e);
   mp_wnd->Invalidate(TRUE);
}

void HostWindow::resizeEvent(QResizeEvent* e)
{
   QWinHost::resizeEvent(e);
   mp_wnd->Invalidate(TRUE);
}

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It'd be nice if QWinHost did this itself!