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：