android 简单联网判断

1. 通过getSystemService获取ConnectivityManager实例，
2. ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(CONNECTIVITY_SERVICE);  
3.          NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();  
4.          if(networkInfo == null || !networkInfo.isAvailable()){  
5.              //当前有可用网络  
6.        }
7. else{  
8.              //当前无可用网络  
9.            }