<asp:button runat="server" ID="btn" text="Button" OnClick="aa_Click" />

public void page_load(Object obj,EventArgs e)
{
  btn.Attributes.Add("onclick","state=true;");
  StringBuilder sb=new StringBuilder();
  sb.Append("if (!state) return;");
  sb.Append("var button=document.getElementById('btn');");
  sb.Append("button.value='Please Wait...';");
  sb.Append("document.body.style.cursor='wait';");
  sb.Append("button.disabled=true;");
  string strScript="<script>";
  strScript=strScript +"var state=false;";
  //将函数绑定到页面的onbeforeunload事件:
  strScript=strScript +"window.attachEvent('onbeforeunload',function(){" +sb.ToString()+ "});";
  strScript=strScript +"</"+"script>";
  Page.RegisterStartupScript("onbeforeunload",strScript);
}
    protected void aa_Click(object sender, EventArgs e)
    {
        //模拟长时间的按钮处理
        System.Threading.Thread.Sleep(2000);
        Response.Write("<script>alert('bbbbbb!!');" + "</" + "script>");
    }