Issues porting code from QtQuick.Controls to Qt.labs.controls

Smatcher

Hello everyone.

I am currently trying to port some code from Quick Controls to the new lab controls.
As suggested by the documentation I made a Qml module (MyControls) wrapping either the old controls or the new controls

This works for most types, however, I encountered a crash with the ScrollBar and ButtonGroup attached properties
Here is some minimalist code illustrating the issue (the lines causing a crash are commented out)

import QtQuick 2.5
import QtQuick.Window 2.2
import QtQuick.Dialogs 1.2

import MyControls 1.0
import Qt.labs.controls 1.0 as LabCtrl

Window {
    title: qsTr("Hello World")
    width: 640
    height: 480
    visible: true

    ButtonGroup {
        id: grp
    }

    Row {
        id: row

        RadioButton {
            text: "hello"
            //ButtonGroup.group: grp // !!! This will crash !!!
            LabCtrl.ButtonGroup.group: grp // !!! This works !!!
        }

        RadioButton {
            text: "bye"
            //ButtonGroup.group: grp // !!! This will crash !!!
            LabCtrl.ButtonGroup.group: grp // !!! This works !!!
        }
    }

    Flickable {
       anchors.top: row.bottom
       width: 200
       height: 100
       contentWidth: 200
       contentHeight: 200
       clip: true

       //LabCtrl.ScrollBar.vertical: ScrollBar{} // !!! This will crash !!!
       //LabCtrl.ScrollBar.vertical: LabCtrl.ScrollBar{} // !!! This will crash !!!

       Rectangle {
         width: 200
         height: 200
         gradient: Gradient {
           GradientStop {position: 0.0; color: "red"}
           GradientStop {position: 0.5; color: "green"}
           GradientStop {position: 1.0; color: "blue"}
         }
       }
    }
}

In the provided example the MyControls module just wraps RadioButton, ButtonGroup and ScrollBar. The qml files are just

import Qt.labs.controls 1.0
RadioButton {}

import Qt.labs.controls 1.0
ButtonGroup {}

import Qt.labs.controls 1.0
ScrollBar {}

Has anyone faced a similar issue ? (I couldn't find any bug report for this specific crash)
Having to import Qt.labs.controls to refer to the attached property of the initial control type seems to defeat the purpose of using a wrapper module (and doesn't work for the ScrollBar type).
What is the best practice in this situation ?

Stepping in the Qt code I noticed that the crash occurs inside the function QQmlObjectCreator::setPropertyBinding()
The code fails to resolve the attached type and uses the null pointer to QQmlType anyway.
Qt crashes instead of printing useful debug information.

I haven't submitted a bug report yet. I will do it when I have more information on this issue.

tmichals

This post is deleted!

jpnurmi

Hi, sounds like a bug in the QML engine. Please report a bug. Thanks!

Smatcher

@jpnurmi

Done. Here is the link for reference https://bugreports.qt.io/browse/QTBUG-53137