Motif/Xt: Trigger reconfiguration of a widget

[Holger Sebert]

On 10/28/21 09:09, Marc Balmer wrote:
>> I am working on Motif code, so please excuse if this mailing list is
>> not the right place for asking my question, but since Motif is based on
>> libXt, I thought I'll give it a try. --
>>
>> I would like to add and remove CascadeButtons dynamically to and from
>> a menubar (a.k.a RowColumn widget).
>>
>> For each addition of a button I create a completely new menubar
>> containing the button(s) to be added and set it in the MainWindow via:
>>
>>     XtVaSetValues(main_window, XmNmenuBar, new_menubar, NULL);
>>
>> The good news is that the program does not crash :) but the menubar is
>> not updated either. Only when I resize the application window does the
>> menubar get updated and displays the new button(s).
>>
>> So my question is: How can I trigger the reconfiguration of a widget's
>> geometry without having to resize the main window?
> 
> The XmUpdateDisplay() function does exactly this.  Call it with the top level widget as parameter.
> 

Thanks for the hint! Calling XmUpdateDisplay() did not have the desired
effect, however.

It turned out that I have to explicitly do an XtDestroyWidget() on the
old menubar before setting the new one (which I had not yet done). It
seems like -- if you don't do this -- the MainWindow widget keeps a
reference of the old menubar somehow still around, even though it should
have been overwritten by XtVaSetValues(XmNmenuBar).

Best,
Holger