如何在QML ApplicationWindow中获取activeFocusControl的className

import QtQuick 2.0
import QtQuick.Controls 2.0

ApplicationWindow {
    id: mainWindow
    width: 400
    height: 300
    visible: true

    // 定义一个Label控件用于显示activeFocusControl的className
    Label {
        id: focusControlLabel
        anchors.centerIn: parent
        text: "Active Focus Control: " + mainWindow.activeFocusControl.className
    }

    // 定义一些控件用于测试
    Button {
        text: "Button"
        onClicked: {
            console.log("Button clicked")
        }
    }

    TextField {
        placeholderText: "Text Field"
    }

    Rectangle {
        width: 100
        height: 100
        color: "red"
        MouseArea {
            anchors.fill: parent
            onClicked: {
                console.log("Rectangle clicked")
            }
        }
    }
}