Thanks for your reply.
Unfortunately, I'm getting really confused. First, I have difficulty understanding the the way indexes are assigned by Qt Designer to properties. Surely custom properties have indexes even if a custom property sheet does not exist. So does a custom property sheet prevent Qt Designer from assigning a property to a custom property? And what index ranges should be assigned to custom properties? From 0 (as Santosh Reddy suggests) or from mpDefaultPropertySheetExtension.count() , as you suggest? Also custom properties display the correct names given to them when declared with Q_PROPERTY(). What then is the purpose of QDesignerPropertySheetExtension::propertyName()?
What's more confusing is that nothing I do in my custom property sheet extension appears to show up in Qt Designer, even an exit() call or QCoreApplication::exit() does nothing. Furthermore without the use of a debugger I can't be absolutely sure that qt_extension<> returns a non-NULL default property sheet and that my custom property sheet is instantiated.
Very confused.
:(
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