判断是否有网络

public boolean isNetworkAvailable(Activity activity) {    Context context = activity.getApplicationContext();    // 获取手机所有连接管理对象（包括对wi-fi,net等连接的管理）    ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);    if (connectivityManager == null) {        return false;    } else {        // 获取NetworkInfo对象        NetworkInfo[] networkInfo = connectivityManager.getAllNetworkInfo();        if (networkInfo != null && networkInfo.length > 0) {            for (int i = 0; i < networkInfo.length; i++) {                if (networkInfo[i].getState() == NetworkInfo.State.CONNECTED) {                    return true;                }            }        }    }    return false;}