I have a problem with the OnPaint method of CFrameWnd, and I cant seem to figure out what is happening. OnPaint is called approx every 10 ms, which causes the computer to freeze. Checked CPU usage and this app takes up 50%!
The application is a very simple MFC app, which is written in one file.
// Includes are done here...
class MFC_Tutorial_Window : public CFrameWnd
{
std::string data;
public:
MFC_Tutorial_Window()
{
this->data = "";
Create(NULL, "Data Win"); // Create window
}
void OnPaint()
{
CDC* pDC = GetDC();
CString s = CString(this->data.c_str());
RECT rc;
HWND hwnd = this->m_hWnd;
if(hwnd != NULL) {
::GetWindowRect(hwnd, &rc);
rc.top = rc.bottom/2;
if(pDC != NULL && pDC->m_hDC != NULL) {
pDC->DrawText(s, &rc, DT_CENTER);
}
}
}
void UpdateWithNewData(std::string up) {
this->data = up;
Invalidate();
}
DECLARE_MESSAGE_MAP()
};
BEGIN_MESSAGE_MAP(MFC_Tutorial_Window, CFrameWnd)
ON_WM_PAINT()
END_MESSAGE_MAP()
// App class
class MyApp :public CWinApp
{
MFC_Tutorial_Window *wnd;
BOOL InitInstance()
{
wnd = new MFC_Tutorial_Window();
m_pMainWnd = wnd;
m_pMainWnd->ShowWindow(3);
wnd->UpdateWithNewData("Hello world!");
return 1;
}
};
Does anyone know why OnPaint is spammed by the system? Have been staring at this code for ages and I just can't find it.
The CPaintDC destructor has to be called for the repainting flag to be reset. You need to call
beginPaint();
andendPaint();
on yourCDC
which should actually be changed to aCPaintDC
. More importantly, not callingendPaint();
will cause the context to be repainted no matter what.