how to bind to `MouseArea`'s `onDragChanged`?

Question

Qt Creator suggests that the onDragChanged slot exists in MouseArea.

    MouseArea {
        id: mouseArea
        ...
        onDragChanged: console.log('Drag changed')
    }

But at runtime it fails with:

Cannot assign to non-existent property "onDragChanged"

Answer 1

The proper way would be:

drag.onActiveChanged: console.log("Drag active:", drag.active)

This is because drag is a group of properties (under the hood it's a QObject or alike), so you need to reference that group first.

Your initial attempt doesn't work because drag is declared as CONSTANT Q_PROPERTY, which doesn't have a on...Changed signal

Answer 2

Silly workaround (but it works...)

readonly property bool _dragActive: drag.active
on_DragActiveChanged: {
    ... = drag.active
}