qml list的ScrollBar

最近正在试验qml各个控件的性能，就想做个定制的ScrollBar，以下是代码实现

import QtQuick 2.7
import QtQuick.Controls 2.3

Rectangle {
    640
    height:480
        property bool refreshFlag: false
            Rectangle{
                 parent.width
                height: -listView.contentY
                color: "cyan"
                Label{
                    anchors.centerIn: parent
                    text:"下拉刷新"
                    visible: listView.contentYr
                }
            }
            BusyIndicator{
                id:busy
                z:4
                running: false
                anchors.horizontalCenter: parent.horizontalCenter
                anchors.top: parent.top
                anchors.topMargin: parent.height/3
                Timer{
                    interval: 2000
                    running: busy.running
                    onTriggered: { busy.running = false }
                }
            }
            ListView{
                id:listView
                anchors.fill: parent
                model: 30
                onContentYChanged: {
                    if(-contentY > 40)
                    { refreshFlag = true }
                }
                onMovementEnded: {
                    if(refreshFlag){
                        refreshFlag = false
                        busy.running = true
                    }
                }
                onCurrentIndexChanged: {
                    console.log("current index = ",currentIndex)
                }
                delegate: Rectangle{
                     listView.width
                    height: 70
                    color: index%2 ? "red":"yellow"
                    Label{
                        id:txt
                        anchors.centerIn: parent
                        font.pointSize: 20
                        text: index
                    }
                }
                ScrollBar.vertical: ScrollBar {
                    id: scrollBar
                    hoverEnabled: true
                    active: hovered || pressed
                    orientation: Qt.Vertical
                    size: 0.8
                    anchors.top: parent.top
                    anchors.right: parent.right
                    anchors.bottom: parent.bottom
                    contentItem: Rectangle  {
                       implicitWidth: 6
                       implicitHeight: 100
                       radius: width / 2
                       color: scrollBar.pressed ? "#81e889" : "#c2f4c6"

                    }
                }
            }
}

效果：