[DllImport("wininet.dll")]

private extern static bool getInterState(out int conn, int val);

public Form1()  {
InitializeComponent(); 
getNet();
}

//判断当前是否连接入Internet网络
private void getNet()
{
int Out;
if (getInterState(out Out, 0) == true)
{
label1.Text = " 网络已连接！";
}else{
label1.Text = " 网络未成功连接！";
}
}
}