android ；檢查網絡是否可以連接

private boolean isConnected(){  
        ConnectivityManager mConnectivity = (ConnectivityManager) this.getSystemService(CONNECTIVITY_SERVICE);    
        TelephonyManager mTelephony = (TelephonyManager)getSystemService(Context.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裏進行一些數據更新。  
        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;  
        }  
    }