问如何使用ArcGIS检索QML/QT的地图比例尺？

EN

import QtQuick 2.6
import QtQuick.Controls 1.4
import Esri.ArcGISRuntime 100.1

ApplicationWindow {
    id: appWindow
    width: 800
    height: 600
    title: "Untitled"
    MapView {
        id: mainmapview
        attributionTextVisible: false
        anchors.topMargin: 0
        anchors.rightMargin: 0
        anchors.fill: parent
        focus: true
        Map {
            id: mainmap
            BasemapLightGrayCanvasVector {}
        }
        onMapScaleChanged: scaletext.text=mainmapview.scale.toString()

        Text {
            id: scaletext
            x: 10
            y: 10
            width: 285
            height: 45
            text: qsTr("Text")
            font.pixelSize: 12
        }
    }
}