Android学习——动态注册监听网络变化

新建一个BroadcastTest项目，然后修改MainActivity中的代码，如下：

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter=new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");    //广播接收器想要监听什么广播，就在这里添加相应的action
        networkChangeReceiver=new NetworkChangeReceiver();
        registerReceiver(networkChangeReceiver,intentFilter);              //调用resigerReceiver()方法进行注册
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);
    }

    class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent){
//          Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
            ConnectivityManager connectionManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);    //得到系统服务类
            NetworkInfo networkInfo=connectionManager.getActiveNetworkInfo();
            if(networkInfo!=null&&networkInfo.isAvailable()){
                Toast.makeText(context,"network is available",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
            }
        }
    }
}

动态注册的广播接收器一定要取消注册才行，在onDestroy()方法中通过调用unregisterReceiver()方法来实现。

访问系统的网络状态需要声明权限，打开AndroidManifest.xml文件，在里面加入权限，如下：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.administrator.broadcasttest">

    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

运行程序，打开数据连接、关闭数据连接，效果如下：