defaut页面：
    protected void Page_Load(object sender, EventArgs e)
    {
        WebUserControl1.SayHellEvent += delegate { SayHello(); };
    }

    private void SayHello()
    {
        Response.Write("Hello World");
    }

WebUserControl:
    public delegate void SayHello();
    public event SayHello SayHellEvent;
    
    protected void Button1_Click(object sender, EventArgs e)
    {
        SayHellEvent(); 
    }