InvalidateRect in WM_CREATE does not work

Question

I want to invalidate the window when it's created. How can I do that? calling InvalidateRect during WM_CREATE doesn't work.

The thing is I call SetWindowLongPtr in WM_CREATE and set GWLP_USERDATA. WM_PAINT looks for some pointer in USER_DATA but the first time I receive WM_PAINT the data isn't apparently still there so it doenst paint my stuff.

Also tried this:

#define MyDefinedMsg (WM_APP+1)
//...//
case WM_CREATE:
  //...//
  SetWindowLongPtr(hWnd,GWLP_USERDATA,ptr);
  PostMessage(hWnd,MyDefinedMsg,0,0);

  break;
case MyDefinedMsg: 
  InvalidateRect(hWnd,NULL,TRUE);
  break;

but did not work.

Thanks in advance

Answer 1

1. Your window is already invalid when it is created
2. PostMessage puts a message in the queue so is likely to arrive after the regular creation messages (WM_CREATE/WM_SIZE/WM_PAINT etc).

If your painting is failing due to GWLP_USERDATA being NULL then something else is happening...

Answer 2

Try ::UpdateWindow(...) after ::CreateWindow(...) call instead sending your message.