dropdownlist onselectedIndexChanged问题

Question

我在我的asp页面中放置了一个下拉列表

 <asp:DropDownList ID="authorList" runat="server"     
  OnSelectedIndexChanged="authorList_Changed" AutoPostBack="true"
   ></asp:DropDownList>

然后在codebehind中，我将它绑定到数据库中的一个字段，然后激活selectedindexchanged

  protected void Page_Load(object sender, EventArgs e)
    {

        var a = (from s in p.Authors
                 select s.FirstName);
        authorList.DataSource = p.Authors;
        authorList.DataTextField = "Firstname";
        authorList.DataValueField = "FirstName";
        authorList.DataBind();
        authorList.SelectedIndexChanged += new EventHandler(authorList_Changed); 
        var q = (from s in p.Authors
                 where s.FirstName.Contains("m") 
                 select s);
        Grid1.DataSource = q;
        Grid1.DataBind();
       // authorList.DisplayMember = "FirstName";
    }
    public void authorList_Changed(Object sender, EventArgs e)
    {
        //Author a = (Author) authorList.SelectedItem;   
        var a = authorList.SelectedValue;
        var v = authorList.SelectedItem;
        var q2 = (from s in p.Authors
                  from w in p.Payrolls
                  where authorList.SelectedValue == s.FirstName
                  where s.AuthorID == w.AuthorID
                  select w);
        List<Payroll> d = q2.ToList();
        if (d.Count > 0)
        {
            payroltextbox.Text = d.First().PayrollID.ToString();
            //authorList.DataBind();
        }
        else
            payroltextbox.Text = "";
           // authorList.DataBind();

    }
    PublishingCompanyEntities p = new PublishingCompanyEntities();

但问题是当我的下拉列表值为1 2 3 4 ....... 1带默认值.......所以，当我选择4时它仍会在回发时返回1并返回文本框（payroltextbox）中的值与1相关联。你可以帮帮我.....

Answer 1

这是因为您忘记在Page_Load中检查Page.IsPostback ...

每次加载页面时都会发生Page_Load，即使它是在回发时也是如此，因此在authorList_Changed事件之前重新填充第一个dropdown。这导致最重要的项目被重新选择。

请参阅Page Lifecycle。

并将您的数据绑定代码放在一个if语句中的Page_Load中，如下所示：

  protected void Page_Load(object sender, EventArgs e)
    {
       if(!Page.IsPostback)
       {
          var a = (from s in p.Authors
                   select s.FirstName);
          authorList.DataSource = p.Authors;
          authorList.DataTextField = "Firstname";
          authorList.DataValueField = "FirstName";
          authorList.DataBind();
          authorList.SelectedIndexChanged += new EventHandler(authorList_Changed); 
          var q = (from s in p.Authors
                   where s.FirstName.Contains("m") 
                   select s);
          Grid1.DataSource = q;
          Grid1.DataBind();
         // authorList.DisplayMember = "FirstName";
       }
    }