HarmonyOS 鸿蒙Next如何检测是否有网络链接

下述demo可以实现设备从无网络到有网络、设备从有网络到无网络触发相应事件，

import { connection } from '@kit.NetworkKit';
import { BusinessError } from '@kit.BasicServicesKit';

// 创建NetConnection对象
let netCon: connection.NetConnection = connection.createNetConnection();

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';

  aboutToAppear(): void {
    netCon.register((error: BusinessError) => {
      console.log(JSON.stringify(error));
    });

    netCon.on('netAvailable', (data: connection.NetHandle) => {
      console.info("netAvailable Succeeded to get data: " + JSON.stringify(data));
    });

    netCon.on('netLost', (data: connection.NetHandle) => {
      console.info("netLost Succeeded to get data: " + JSON.stringify(data));
    });
  }

  build() {
    RelativeContainer() {
      Text(this.message)
        .id('HelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .alignRules({
          center: { anchor: '__container__', align: VerticalAlign.Center },
          middle: { anchor: '__container__', align: HorizontalAlign.Center }
        })
    }
    .height('100%')
    .width('100%')
  }
}