主要思路：使用Android中的四大元件之：BrocastReceiver監聽網路狀態的變化。接收到網路狀態改變的廣播之後判斷當前的網路是否可用。

建立廣播接收器MyNetworkReceiver

public class MyNetworkReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        //**判斷當前的網路連線狀態是否可用*/
        ConnectivityManager connectivityManager = 
        (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = connectivityManager.getActiveNetworkInfo();
        if
 
 ( info != null && info.isAvailable()){
            //當前網路狀態可用
            int netType = info.getType();
            if (netType == ConnectivityManager.TYPE_WIFI){
                Log.e("NETSTATUE", "當前網路狀態為-wifi");
            }else if (netType == ConnectivityManager.TYPE_MOBILE ){
                Log.e("NETSTATUE"
 
, "當前網路狀態為-mobile");
            }
        }else {
            //當前網路不可用
            Log.e("NETSTATUE", "無網路連線");
        }
    }
}

一、BroadcastReceiver的用法之靜態註冊：
在AndroidManifest清單檔案中註冊廣播接收器

<receiver
     android:name=".MyNetworkReceiver">
     <intent-filter>
            <action  android:name
 
="android.net.conn.CONNECTIVITY_CHANGE"/>
     </intent-filter>
</receiver>

二、BroadcastReceiver的用法之動態註冊
可以在Activity的OnCreate()方法中註冊onDestory()方法中登出
亦可以再Application的onCreate()方法中註冊onTerminate()方法中登出
註冊：

receiver = new YunNetworkReceiver();
IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
registerReceiver(receiver,intentFilter);

登出：

unregisterReceiver(receiver);