The solution that the Tab control in QML TabView cannot access the child control id

import QtQuick 2.12

import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12
import QtQml 2.0
TabView {
    property string font_color: "#EFEFEF";
    onCurrentIndexChanged:
    {
        if(currentIndex==0)
        {
            //console.log("onLoaded ipaddress = ",ipaddress);
            last_tab.reset_ip();
            //这里是切换tab页的时候，根据当前切换的下标进行调用，可以根据Tab的index进行动态绘制其中的内容
        }
    }
    Tab {
        property Item  ip_label:null
        property Item  ip_text:null
        id: last_tab
        anchors.topMargin:40
        anchors.bottomMargin:160
        anchors.leftMargin: 100

        function reset_ip(){
            if(ip_label != null){
                if(ip_text.visible){
                    var ipaddress = config.ipv4_address().trim();
                    ip_text.text = ipaddress;
                }
            }
        }
        onLoaded:{
            ip_label = item.ip_label
            ip_text = item.ip_text
            //关键在这里，动态链接到实例化后的item中的属性。
            //item是Tab中的一个成员变量，是实例化后的具体子控件的对象
        }
        GridLayout {
            property Item  ip_label:ip_address_label
            property Item  ip_text:ip_address_text
            id:grid_layout
            anchors.fill: parent
            columns: 2
            flow: GridLayout.LeftToRight
            Label 
            {
                id:ip_address_label;
                text: "IP 地址";
                color: font_color;
                font.pixelSize: 18;
                visible:config.ipv4_address().trim() != "";

            }
            Text {
                id:ip_address_text
                text: config.ipv4_address().trim()
                font.pixelSize: 18
                color: font_color
                visible:config.ipv4_address().trim() != ""
            }
  
}