dynamic_cast fails

[Maxwell Chen]

There is an Edit control on the dialog. The ID is IDC_EDIT. In CMyDialog::OnInitDialog(), I do this ...

CEdit* pEdit = dynamic_cast<CEdit*>(GetDlgItem(IDC_EDIT) /* = some valid address */);
if(!pEdit) {
// Error;
}

The CWnd* returned from GetDlgItem failed to convert to a CEdit*. But isn't CEdit derived from CWnd? :confused:

Maxwell Chen

[Lost User]

Hi Maxwell,

Maxwell Chen wrote:

But isn't CEdit derived from CWnd

Yes, but GetDlgItem does not always return a CEdit pointer so the dynamic_cast runtime check fails. Have a look at the following document: Inside MFC: Handle Maps and Temporary Objects[^] Essentially... when GetDlgItem cannot find a permanent object in the MFC CHandleMap it will return a pointer to a CTempWnd object. So your code fails to dynamic_cast from CTempWnd to CEdit. As an experiment you should add a CEdit member variable to your class for IDC_EDIT. This will cause the CHandleMap to have a permanent handle. Now your code will magically work. :) Best Wishes, -David Delaune

[Maxwell Chen]

Thank you! ;)

Maxwell Chen