DOC: GetClientRect() May Assert in OLE Controls (138664)

SUMMARY

In chapter 4 of the Ole Control Tutorial, the section labeled Setting the CircleOffset Property Step 2, which describes how to implement the InBounds() function, incorrectly calls GetClientRect() and should read as follows instead:

Add the function implementation at the end of your CIRCCTL.CPP file:

      BOOL CCirc2Ctrl::InBounds(short nOffset)
      {
         int diameter;
         int length;
         int cx;
         int cy;

        // Note that GetControlSize() is called here instead of
        // GetClientRect()

         GetControlSize(&cx, &cy);

         if (cx > cy)
         {
            length = cx;
            diameter = cy;
         }
         else
         {
            length = cy;
            diameter = cx;
         }
         if (nOffset < 0)
            nOffset = (short) -nOffset;
         return (diameter / 2 + nOffset) <= (length / 2);
      }

This documentation error was corrected in Visual C++ version 5.0.

MORE INFORMATION

In some control containers (such as Visual Basic and Microsoft Access) in design mode, the control has no window, and therefore no hwnd, so calling GetClientRect(rc) will assert.

There are actually two solutions to this problem. The first solution is documented in the "Summary" section of this article. The second solution is to replace the call to GetClientRect() with a call to GetRectInContainer(), which will obtain the coordinates of the control's rectangle relative to the container. The size of the control can then be calculated from this rectangle.