FIX: Assertion, VIEWSCRL.CPP, Line 455 with SetScaleToFitSize (113588)

SYMPTOMS

Calling SetScaleToFitSize in OnInitialUpdate of a CFormView derived class causes the following assertion to fail:

File viewscrl.cpp, Line 455, Assertion Failed!

CAUSE

Because the view window has not yet been displayed, SetScaleToFitSize() uses the size of the CFormView. Because the CFormView is created with size CRect(0,0,0,0), the view size is miscalculated.

RESOLUTION

To set the view window size before calling SetScaleToFitSize, call RecalcLayout on the parent frame. For example:

   GetParentFrame()->RecalcLayout();

See the sample code below for an example of this.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft Foundation Classes (MFC) version 2.0. This problem was corrected in the Microsoft Foundation Classes version 2.5.

MORE INFORMATION

The call to RecalcLayout in OnInitialUpdate is no longer needed with MFC version 2.5 because the framework takes care of calling RecalcLayout in response to the WM_CREATE message before the call to OnInitialUpdate is made.

Sample Code

/*  Compile options needed: none
*/ 

void CMyFormView::OnInitialUpdate()
{
    CFormView::OnInitialUpdate();     // Base class initialization.

    //GetParentFrame()->RecalcLayout  // Uncomment to fix. No need to
                                      // call if this is version 2.5.
    CSize mysize(100,100);

    SetScaleToFitSize(mysize);        // This will ASSERT in version
                                      // 2.0 unless RecalcLayout is
                                      // called.
}