what to do to make windows non-resizable?

[wysota]

I added:

layout() -> setSizeConstraint ( QLayout :: SetFixedSize ) ;

layout() -> setSizeConstraint ( QLayout :: SetFixedSize ) ;

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at line 40 of ui.cpp but now I get a very tiny window which shows nothing. I am now unable to resize the window which would be good except I can't see anything at all.

It probably means you didn't apply a layout to the form or somewhere lower in the hierarchy.

I also don't understand why setting the sizePolicy to Fixed isn't enough to do this.

Because sizePolicy only works for a widget that is inside a layout and obviously a top-level window (like yours) is not inside one.