有无可用网络 Android中判断有无可用网络的代码(是否是3G或者WIFI网络)

ConnectivityManager mConnectivity = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
TelephonyManager mTelephony = (TelephonyManager)this.getSystemService(TELEPHONY_SERVICE);
//检查网络连接，如果无网络可用，就不需要进行连网操作等
NetworkInfo info = mConnectivity.getActiveNetworkInfo();

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

//判断网络连接类型，只有在3G或wifi里进行一些数据更新。
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;
}