使用PrintWindow截屏后，WinAPI Window不再更新

Question

I am taking screenshots of an application using PrintWindow() . The application contains a listview and after some time, the list does not update anymore. Only when I select an entry in the list, does it update the name of that entry. My assumption is that the ListView's window does not get invalidated somehow, but that's just a guess. I tried calling InvalidateRect() after taking the screenshot, but that doesn't help either.

I thought the reason for this must be a resource leak, but I encapsulated all required resources in a class, that automatically handles releasing them.

struct DrawingSurface
{
  DrawingSurface(const DrawingSurface&) = delete;
  DrawingSurface& operator=(const DrawingSurface&) = delete;

  // Window is a custom class, but it's not really important here.
  DrawingSurface(const Window& window)
  : hwnd(window.handle()), pixels(0), windowDC(0), memoryDC(0), bitmap(0), previous(0)
  {
    // Get window size.
    Rect clientRect = window.getClientRect();
    width = clientRect.width();
    height = clientRect.height();
    // Create DCs.
    windowDC = ::GetDC(window.handle());
    if(windowDC == NULL)
      return;
    memoryDC = ::CreateCompatibleDC(windowDC);
    if(memoryDC == NULL)
      return;
    // Create bitmap.
    ZeroMemory(&bitmapInfo, sizeof(BITMAPINFO));
    bitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bitmapInfo.bmiHeader.biWidth = width;
    bitmapInfo.bmiHeader.biHeight = -height;
    bitmapInfo.bmiHeader.biPlanes = 1;
    bitmapInfo.bmiHeader.biBitCount = 32;
    bitmapInfo.bmiHeader.biCompression = BI_RGB;
    bitmapInfo.bmiHeader.biSizeImage = width * height * 4;
    bitmap = ::CreateDIBSection(windowDC, &bitmapInfo, DIB_RGB_COLORS, (void**)&pixels, 0, 0);
    if(bitmap == NULL)
      return;
    previous = ::SelectObject(memoryDC, bitmap);
  }
  ~DrawingSurface()
  {
    if(windowDC != NULL)
      ::ReleaseDC(hwnd, windowDC);
    if(previous != NULL && previous != HGDI_ERROR && memoryDC != NULL)
      ::SelectObject(memoryDC, previous);
    if(memoryDC != NULL)
      ::DeleteDC(memoryDC);
    if(bitmap != NULL)
      ::DeleteObject(bitmap);
  }
  bool valid() const
  {
    return width * height > 0
        && previous != NULL
        && previous != HGDI_ERROR
        && windowDC != NULL
        && memoryDC != NULL
        && bitmap != NULL;
  }
  int width, height;
  HWND hwnd;
  HDC windowDC;
  HDC memoryDC;
  HBITMAP bitmap;
  RGBQUAD* pixels;
  BITMAPINFO bitmapInfo;
private:
  HGDIOBJ previous;
};

I then use this drawing surface to take a screenshot with this function:

bool Screenshot::take(const Window& window)
{
  m_width = 0; m_height = 0;
  DrawingSurface surface(window);
  if(!surface.valid())
    return false;
  if(PrintWindow(surface.hwnd, surface.memoryDC, PW_CLIENTONLY) == 0)
    return false;
  if(GdiFlush() == 0)
    return false;
  // Set attributes.
  m_hwnd = surface.hwnd;
  m_width = surface.width;
  m_height = surface.height;
  // Copy pixels.
  m_pixels.resize(surface.width * surface.height, { 0, 0, 0, 0 });
  memcpy(&m_pixels[0], surface.pixels, surface.bitmapInfo.bmiHeader.biSizeImage);
  return true;
}

I don't see where I could leak any resources here. Any other ideas why what I described above might happen?

Any help appreciated, thanks.

Answer 1

Thanks everyone for the answers. I was able to solve this myself now and the problem really wasn't related to the screenshot function. Instead I had posted a WM_KEYDOWN message to the ListView, and forgot to post WM_KEYUP as well. This left the ListView in an invalid state and therefore it did not update anymore.

Thanks again for all the answers and especially for helping to verify that there are no resources leaked.