ConnectivityManager mConnectivity = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
TelephonyManager mTelephony = (TelephonyManager)this.getSystemService(TELEPHONY_SERVICE);
//檢查網絡連接，如果無網絡可用，就不需要進行連網操作等
NetworkInfo info = mConnectivity.getActiveNetworkInfo();

if (info == null || !mConnectivity.getBackgroundDataSetting()) {
return false;
}

//判斷網絡連接類型，只有在3G或wifi里進行一些數據更新。
int netType = info.getType();
int netSubtype = info.getSubtype();

if (netType == ConnectivityManager.TYPE_WIFI) {
return info.isConnected();
} else if (netType == ConnectivityManager.TYPE_MOBILE
&& netSubtype == TelephonyManager.NETWORK_TYPE_UMTS
&& !mTelephony.isNetworkRoaming()) {
return info.isConnected();
} else {
return false;
}