public class Net
{
[DllImport("wininet")]
private extern static bool InternetGetConnectedState(out int connectionDescription, int reservedValue);

/// <summary> 
/// 检测本机是否联网 
/// </summary> 
/// <returns></returns> 
public static bool IsConnectedInternet()
{
int i = 0;
if (InternetGetConnectedState(out i, 0))
{
//已联网 
return true;
}
else
{
//未联网 
return false;
}

}

}