[Development] Qt 6.2 QQmlMetaType incompatibility

Uwe Rathmann Uwe.Rathmann at tigertal.de
Fri Sep 24 10:12:53 CEST 2021


when testing the Qt 6.2 rc I noticed that registering custom string 
converters with
QQmlMetaType::registerCustomStringConverter() has been dropped.

( Yes, QQmlMetaType is from the private API where no compatibility 
policies are made )

Actually I'm not interested in having a custom string converters - I was 
using it as a workaround
to be able to create a margin that is made from 4 values ( left, top, 
right, bottom ) from a single
value in QML.

Instead of writing:

               left: 10
               top : 10
               right : 10
               bottom: 10

I would like to have the option to write it that way:

         margins : 10

Here is my solution - one I do not like much - but it worked until Qt 6.2:

For some reason neither the Qt metatype system nor the QML engine has 
specific support for
QMarginsF - like what is implemented for classes other standard Qt types 
like QPointF/QRectF/QSizeF ...

So I derived from QMarginsF and exposed it to QML using Q_GADGET.
See https://github.com/uwerat/qskinny/blob/master/src/common/QskMargins.h

To make the single value assignment possible I added the following:

     QQmlMetaType::registerCustomStringConverter( qMetaTypeId< 
QskMargins >(),
         []( const QString& s ) { return QVariant::fromValue( 
QskMargins( s.toDouble() ) ); } );

Is the a way to accomplish something similar with Qt 6.2 ?


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