how come my extended StackLayoutPanel does show headers correctly?

[Elhanan]

but my extened StackPanel does?

 

i extend the StackPanel and try to place header and vertical panel with a hyperlink they are shown  correctly in the designer but, if i replace it to StackLayoutPanel it does not..

 

however just using a StackLayoutPanel class inside the entry point does show it correctly.

[Eric Clayberg (Google)]

StackLayoutPanel does not provide enough API to get the required design time information (such as the headers). We resort to hacks to get access to that info for StackLayoutPanel itself at design time.

It is unlikely that you can create a compatible sub-class of StackLayoutPanel, because there is no API to be compatible with. You would need to create specific design time support for your class much like we did for StackLayoutPanel. Unless we open source GWT Designer itself, that will be very difficult as the only design time models for you to look at are for SWT and Swing in the WindowBuilder open source project at Eclipse.