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

ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(CONNECTIVITY_SERVICE); 
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo(); 
if(networkInfo == null || !networkInfo.isAvailable()) 
{ 
    //當前有可用網絡 
} 
else  
{ 
    //當前無可用網絡 
}