常用的IM聊天App中都會判斷網路連線是否可用，今天我們就用靜態註冊註冊廣播來監聽網路的變化：首先申請網路許可權

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

  <receiver
            android:name=".NetWorkChangeReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="1000">
                <action android:name="android.net.conn.CONNECTIVITY_CHANGE"/>
            </intent-filter>
        </receiver>
 

package com.example.administrator.broadcastreceiver;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.widget.Toast;

public class NetWorkChangeReceiver extends BroadcastReceiver {
    public NetWorkChangeReceiver() {
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        //Toast.makeText(context,"netChanged!",Toast.LENGTH_LONG).show();
       ConnectivityManager connectivityManager = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
        if(networkInfo !=null && networkInfo.isAvailable())
        {
            Toast.makeText(context,"isAvailable!",Toast.LENGTH_LONG).show();
        }else
        {
            Toast.makeText(context,"unAvailable!",Toast.LENGTH_LONG).show();
        }
    }
}