How to customize ScrollBar of ListView decorated by a custom ScrollView

[teddybeams]

I'm working on porting a project from Qt Quick Controls 1 to Qt Quick Controls 2. In the existing codebase, there's a custom ScrollView which is used in many places to decorate a ListView. With Quick Controls 1, this offered the ability to have custom styling for scroll bars everywhere the custom ScrollView was used via the ScrollViewStyle.

While porting this component, I've refactored the styling to work with Quick Controls 2. However, the scrollbars aren't appearing properly whenever I use this custom ScrollView. The scrollbars appear very small and aren't positioned correctly. It seems like I have to attach to the ScrollBar directly to the ListView to get them to work correctly.

Here's a minimal, reproducible example of what I mean:

A custom ScrollView

// MyScrollView.qml
import QtQuick
import QtQuick.Controls

ScrollView {
    ScrollBar.vertical: ScrollBar {
        background: Rectangle {
            color: "black"
            radius: width/2
        }
        contentItem: Rectangle {
            radius: width/2
            color: "#73D0F9"
            implicitHeight: 8
            implicitWidth: 6
        }
    }
}

main.qml

import QtQuick
import QtQuick.Controls

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

    MyScrollView {
        anchors.fill: parent

        ListView {
            model: 20
            delegate: ItemDelegate {
                text: "Item " + index
                required property int index
            }
        }
    }
}

Produces this:

If I instead attach the ScrollBar to the Listview, everything seems to work, but the default ScrollBar for the ScrollView overlaps with my custom one on the ListView:

//MyScrollView.qml
import QtQuick
import QtQuick.Controls

ScrollView {
}

main.qml

import QtQuick
import QtQuick.Controls

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

    MyScrollView {
        anchors.fill: parent

        ListView {
            ScrollBar.vertical: ScrollBar {
                background: Rectangle {
                    color: "black"
                    radius: width/2
                }
                contentItem: Rectangle {
                    implicitHeight: 6
                    implicitWidth: 8
                    radius: width/2
                    color: "#73D0F9"
                }
            }

            model: 20
            delegate: ItemDelegate {
                text: "Item " + index
                required property int index
            }
        }
    }
}

Produces this:

Why does the ScrollBar not get positioned or scaled correctly in the first example? Is it because the ScrollBar is parented to the ScrollView instead of the ListView? I'm not sure what I'm doing wrong

[Danima]

Try this code

import QtQuick 2.12
import QtQuick.Window 2.15
import QtQuick.Controls 2.13

Window
{
    id:win1
    visible:true
    width:900
    height:300

    ListView {
        id:list
        width: 100
        height:parent.height
        model: 20
        delegate: ItemDelegate {
                text: "Item " + index
                required property int index
            }
        ScrollBar.vertical: vsb
    }

    ScrollBar {
        id: vsb
        width: 16
        anchors.left: list.right
        anchors.top: parent.top
        anchors.bottom: parent.bottom
        orientation: Qt.Vertical
        policy: ScrollBar.AlwaysOn
    }

}