I have a QQuickItem derived C++ class, Foo, and I would like to ensure, that whoever uses it in QML, gives a value to the objectName property. In Foo I am redefining the property like this:
Q_PROPERTY(QString objectName READ objectName WRITE setObjectName NOTIFY objectNameChanged REQUIRED)
Since objectNameChanged does not take zero arguments, this alone leads to an error. So I need to also add a signal to Foo:
void objectNameChanged();
Then it compiles without errors.
The documetation states:
In QML, classes with REQUIRED properties cannot be instantiated unless all REQUIRED properties have been set.
However, when I use it like this in QML:
Foo {
// objectName: qsTr("test) <-- commented line
}
the program compiles and runs without errors.
Is there a way to change the objectName, or any other existing property for that matter, to required?
What you could do is to expose a qml file Foo.qml which contains
CppFoo {
required objectName
}
instead of exposing the C++ class directly to your users. Doing that for instance with a simple Item, and using it in another file would then lead to an error like
file:///tmp/tmp.aOQi2yetXl/Foo.qml:3 Required property objectName was not initialized
The fact that Q_PROPERTY(QString objectName READ objectName WRITE setObjectName NOTIFY objectNameChanged REQUIRED) did not work is probably a bug in the engine. And there's currently no feature in the C++ API to mark the property of a parent's class as required.
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