网络状态发生变化的时候，系统会发出 android.net.conn.CONNECTIVITY_CHANGE ，直接上代码。

package mark.zhang;

import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.IBinder;
import android.util.Log;

public class ListenNetStateService extends Service {
    private ConnectivityManager connectivityManager;
    private NetworkInfo info;

    private BroadcastReceiver mReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(ConnectivityManager.CONNECTIVITY_ACTION)) {
                Log.d("mark", "网络状态已经改变");
                connectivityManager = (ConnectivityManager)      

                                         getSystemService(Context.CONNECTIVITY_SERVICE);
                info = connectivityManager.getActiveNetworkInfo();  
                if(info != null && info.isAvailable()) {
                    String name = info.getTypeName();
                    Log.d("mark", "当前网络名称：" + name);
                } else {
                    Log.d("mark", "没有可用网络");
                }
            }
        }
    };

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        IntentFilter mFilter = new IntentFilter();
        mFilter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
        registerReceiver(mReceiver, mFilter);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        unregisterReceiver(mReceiver);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return super.onStartCommand(intent, flags, startId);
    }
}

在 manifest 文件中需要加上一条权限：

 <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

在Android操作系统中，如何能够正确的判断我们所连接的网络是否断开恩？今天我们就针对这一应用技巧进行一个详细的分析。

public class ConnectionChangeReceiver extends BroadcastReceiver {   
        @Override   
        public void onReceive( Context context, Intent intent ) {   
            ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);   
            NetworkInfo activeNetInfo = connectivityManager.getActiveNetworkInfo();   
            NetworkInfo mobNetInfo = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);   
            if ( activeNetInfo != null ) {   
                Toast.makeText( context, "Active Network Type : " +
                      activeNetInfo.getTypeName(), Toast.LENGTH_SHORT ).show();   
                }   
            if( mobNetInfo != null ) {   
                Toast.makeText( context, "Mobile Network Type : " +
                      mobNetInfo.getTypeName(), Toast.LENGTH_SHORT ).show();   
                }   
          }   
    }

< !-- Needed to check when the network connection changes -->   

  < uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>   
  < receiver android:name="com.blackboard.androidtest.receiver.ConnectionChangeReceiver"   
             android:label="NetworkConnection">   
      < intent-filter>   
          < action android:name="android.net.conn.CONNECTIVITY_CHANGE"/>   
      < /intent-filter>   
  < /receiver>