如何判断当前网络能否上网
============

可以使用@ohos.net.connection的能力，在网络连接状态发生变化时，判断当前网络是否可以访问互联网，并将判断结果存储到AppStorage中。需要判断网络连接状态时，直接从AppStorage获取结果。参考代码如下：

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


@Entry
@Component
export struct NetJudge {
  public static netConnection: connection.NetConnection | undefined = undefined;
  private static JUDGE\_NET\_TAG: string = 'NetJudge.currNet.isUseful';

  init() {
    NetJudge.netConnection = connection.createNetConnection();
    NetJudge.netConnection.register(() => {
      console.info('connection register success');
    });

    NetJudge.netConnection.on('netAvailable', (data) => {
      console.info('NetJudge  netAvailable ');
      AppStorage.setOrCreate(NetJudge.JUDGE\_NET\_TAG, this.judgeHasNet());
    });

    NetJudge.netConnection.on('netUnavailable', () => {
      console.info('NetJudge  netUnavailable ');
      AppStorage.setOrCreate(NetJudge.JUDGE\_NET\_TAG, this.judgeHasNet());
    });

    NetJudge.netConnection.on('netCapabilitiesChange', (data: connection.NetCapabilityInfo) => {
      AppStorage.setOrCreate(NetJudge.JUDGE\_NET\_TAG, this.judgeHasNet());
    });

    _// Subscribe to network connection information change events. You can only receive this event notification after calling register_
    NetJudge.netConnection.on('netConnectionPropertiesChange', (data: connection.NetConnectionPropertyInfo) => {
      AppStorage.setOrCreate(NetJudge.JUDGE\_NET\_TAG, this.judgeHasNet());
    });

    NetJudge.netConnection.on('netLost', () => {
      AppStorage.setOrCreate(NetJudge.JUDGE\_NET\_TAG, this.judgeHasNet());
    });
  }

  regist() {
    if (NetJudge.netConnection === undefined) {
      this.init();
    }
  }

  judgeHasNet(): boolean {
    try { _// Get current network connection_
      let netHandle = connection.getDefaultNetSync();

      _// 0-100 Reserved connections for the system_
      if (!netHandle || netHandle.netId < 100) {
        return false;
      }

      _// Get the properties of the connection_
      let netCapability = connection.getNetCapabilitiesSync(netHandle);
      let cap = netCapability.networkCap;
      if (!cap) {
        return false;
      }

      for (let em of cap) {
        if (connection.NetCap.NET\_CAPABILITY\_VALIDATED === em) {
          return true;
        }
      }
    } catch (e) {
      let err = e as BusinessError;
      console.info('get netInfo error ：' + JSON.stringify(err));
    }
    return false;
  }

  build() {
    Column({ space: 10 }) {
      Button('如何判断当前网络能否上网')
        .onClick(() => {
          this.regist();
        })
    }
    .alignItems(HorizontalAlign.Center)
    .height('100%')
    .width('100%')
  }
}