Question

I am trying to make a Visual C++ 2008 program that plots some data in a Window. I have read from various places the correct way to do this is to override WndProc. So I made a Windows Forms Application in Visual C++ 2008 Express Edition, and I added this code to Form1.h, but it won’t compile:

    public:     [System::Security::Permissions::PermissionSet(System::Security::Permissions::SecurityAction::Demand, Name='FullTrust')]     virtual void WndProc(Message %m) override     {         switch(m.Msg)         {             case WM_PAINT:             {                 HDC     hDC;                 PAINTSTRUCT ps;                 hDC = BeginPaint(m.HWnd, &ps);                  // i'd like to insert GDI code here                  EndPaint(m.Wnd, &ps);                 return;             }         }         Form::WndProc(m);     } 

When I try to compile this in Visual C++ 2008 Express Edition, this error occurs: error C2664: ‘BeginPaint’ : cannot convert parameter 1 from ‘System::IntPtr’ to ‘HWND’

When I try using this->Handle instead of m.HWnd the same error occurs.

When I try casting m.HWnd to (HWND), this error occurs: error C2440: ‘type cast’ : cannot convert from ‘System::IntPtr’ to ‘HWND’

Maybe I need to cast the m.HWnd to a pin_ptr or something.

Answer 1

If you were making a raw Win32 application then you could use those functions.

If, on the other hand, you are making a WinForms application then you need to override the OnPaint event.

• Switch to the design view (The view that shows your form.)
• Click on the title bar of your form
• In the properties window (by default probably on your lower right screen) select the lightning bolt near the top. This will display a list of events.
• Scroll down to the paint event and double click it.

You will end up with a Paint routine shell from which you can use the drawing functions of the graphics object.

 private: System::Void Form1_Paint(System::Object^  sender, System::Windows::Forms::PaintEventArgs^  e)  {     e->Graphics->DrawRectangle(...)               } 

If you really want to write raw Win32 code, let me know, and I can help you write a shell. In the time being if you are interested in Win32 I recommend Charles Petzold’s Programming Windows 5th edition.

If you want to learn C++ WinForms… well, I recommend switching to C# or VB.NET simply because they might be more intuitive.

Hope this helps. Cheers.