dropdownlist不会在SelectedItemChanged上触发

Question

I have a DDL within an update panel and I cannot get the SelectedItemChanged method to fire when I bind data to it. In Page_Load I have:

ddl.DataSource = GetList();
ddl.DataBind();

GetList() returns a List<string>

The values are all there but nothing happens when I select one.

If I am to manually put them in like so:

ddl.Items.Add("1");
ddl.Items.Add("2");
ddl.Items.Add("3");

it works, why?

The method below is never entered into if I bind the data.

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {
        string test = ddl.SelectedItem.Text;
    }

<asp:DropDownList runat="server" ID="ddl" Width="150px"
OnSelectedIndexChanged="ddl_SelectedIndexChanged"></asp:DropDownList>

Answer 1

By default the Change asp:DropDownList does not do postback like button as that is not required in many cases. You have to set it to true to get the postback.

Change

<asp:DropDownList runat="server" ID="ddl" Width="150px"
OnSelectedIndexChanged="ddl_SelectedIndexChanged"></asp:DropDownList>

To

<asp:DropDownList runat="server" ID="ddl" Width="150px" AutoPostBack="true"
OnSelectedIndexChanged="ddl_SelectedIndexChanged"></asp:DropDownList>

Answer 2

请在DropDownList上设置属性AutoPostBack =“ true”（如果尚未设置），这将允许下拉列表回发任何SelectedIndex更改