CanAutoSize is called automatically when the AutoSize property is True and an attempt to resize the control is made to resize the control. It allows controls to implement the AutoSize property before the resize sequence. This sequence begins with the OnCanResize and OnConstrainedResize events and ends with the OnResize event. When CanAutoSize is called, the NewWidth and NewHeight parameters indicate the proposed new dimensions of the control bar. CanAutoSize adjusts these values so that the control bar’s bands are all visible. CanAutoSize returns True, indicating that the resize sequence should proceed. 

CreateWnd 

CreateWindowHandle