Re: Getting owner draw child control to paint when calling SetWindowText

"Doug Harrison [MVP]" <>
Fri, 18 Apr 2008 14:13:41 -0500
On Fri, 18 Apr 2008 18:47:59 +0100, "J M" <> wrote:


I have an owner draw static class. DrawItem is called (and works ok) when
the dialog repaints, i.e. initially and when restored, but my class DrawItem
is not called when SetWindowText is called.

Is there some way to get a dialog to request an owner draw child control to
paint itself other than calling Invalidate() and UpdateWindow() in the
dialog class (which draws all the controls and in my app results in an
endless loop as the static text is changed by a slider control)?



Some detail omitted for clarity:

class ColorStatic : public CStatic


 CFont m_TextFont;
 COLORREF m_rgbTextColor;

 virtual void DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct);


 virtual void PreSubclassWindow();

void ColorStatic::DrawItem(LPDRAWITEMSTRUCT /*lpDrawItemStruct*/)
CPaintDC dc(this); // lpDrawItemStruct unused so we can call DrawItem
directly if needed

HFONT hOldFont = (HFONT) dc.SelectObject(m_TextFont);

dc.SetTextAlign(TA_TOP | TA_LEFT);

CString strText;


dc.TabbedTextOut(0, 0, strText, 0, NULL, 0);


The problem is that your use of CPaintDC is invalid:

1. You must use the HDC the WM_DRAWITEM message gives you.

2. You must not use CPaintDC (really BeginPaint/EndPaint under the hood)
outside of WM_PAINT messages, and then you must be the only one using it.
(The fact that DRAWITEMSTRUCT gives you an HDC means you shouldn't be using

As for your comment:

// lpDrawItemStruct unused so we can call DrawItem directly if needed

From where do you call it directly? You should never need to draw anything
except in response to WM_DRAWITEM messages. Sometimes it's useful to
delegate WM_DRAWITEM phases to separate functions, and I've done that for
listboxes with:

   virtual void DrawItemBackground(
         CDC& dc,
         const CRect& rc,
         int ixItem,
         DRAWITEMSTRUCT& dis);

   virtual void DrawItemContents(
         CDC& dc,
         const CRect& rc,
         int ixItem,
         DRAWITEMSTRUCT& dis);

   virtual void DrawItemFocus(
         CDC& dc,
         const CRect& rc,
         int ixItem,
         DRAWITEMSTRUCT& dis);

Of course, it is DrawItem that calls these functions.

Doug Harrison
Visual C++ MVP

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