代码 

1. ConnectivityManager con=(ConnectivityManager)getSystemService(Activity.CONNECTIVITY_SERVICE);  
2. boolean wifi=con.getNetworkInfo(ConnectivityManager.TYPE_WIFI).isConnectedOrConnecting();  
3. if(wifi){  
4.     //执行相关操作  
5. }else{  
6.     Toast.makeText(getApplicationContext(), "当前为非WiFi网络，注意流量哦--", Toast.LENGTH_LONG).show();  
7. }  

 权限

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />