<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /><intent-filter>   <action android:name="android.net.conn.CONNECTIVITY_CHANGE" /></intent-filter>

@Overrideprotected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);  checkNetwork();  if (!checkNetwork()) {    Toast.makeText(this, "沒有網絡", Toast.LENGTH_LONG).show();    Intent intent = new Intent("android.settings.WIRELESS_SETTINGS");    startActivity(intent);    return;  }}private boolean checkNetwork() {  ConnectivityManager conn = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);  NetworkInfo net = conn.getActiveNetworkInfo();  if (net != null && net.isConnected()) {    return true;  }  return false;}