监听手机网络状态变化

 private BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(ConnectivityManager.CONNECTIVITY_ACTION)) {
                connectivityManager = (ConnectivityManager)
                        getSystemService(Context.CONNECTIVITY_SERVICE);
                info = connectivityManager.getActiveNetworkInfo();
                if (info != null && info.isAvailable()) {
                    //网络可用时，执行的代码

                    return;
                }

                //网络不可用时，执行的代码      
            }
        }
    };

注册接受网络状态改变接收器

 IntentFilter mFilter = new IntentFilter();
 mFilter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
 registerReceiver(mReceiver, mFilter);

Manifest加上权限

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