C# 检查网络是否连通

[DllImport("wininet.dll")]
private extern static bool InternetGetConnectedState(out int connectionDescription, int reservedValue);
private bool IsConnected()
        {
int I = 0;
bool state = InternetGetConnectedState(out I, 0);
return state;
        }

bool state = IsConnected();   //True 为连通   False 为断开