关于重载oninit方法

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Response.Write("页加载");
        Response.Write(textbox1.Text);
    }
    protected override void OnInit(EventArgs e)
    {
        Response.Write(textbox1.Text);
    }
    protected void click(object sender, EventArgs e)
    {

    }
}


请问一下。为何oninit只会第一次请求时会执行，当回传服务器后，oninit就不会再执行啦呢？还是。这里的oninit是方法还是事件呢？