DropDownList 所选项目始终是列表中的第一项

Question

我在用户控件中有一个 DropDownList；但是，无论我做什么，我都无法正确填充任何“选定”属性（SelectedItem、SelectedIndex、SelectedValue）。这三个属性的值都是我列表中的第一项，无论实际选择了哪个项目。

<asp:DropDownList ID="ParticipantsSelectList" runat="server">
    <asp:ListItem Value="">Please select a team...</asp:ListItem>
    <asp:ListItem value="{D37EFA0C-988A-4A2A-8D6E-80E3BAE00DEE}">Blue Team</asp:ListItem>
    <asp:ListItem value="{7543E282-C9B8-435A-86A2-70E8E3BB38E5}">Green Team</asp:ListItem>
    <asp:ListItem value="{F6BEF34A-215E-4179-9F4C-68F7C43D755F}">Orange Team</asp:ListItem>
    <asp:ListItem value="{D50AD44A-686A-4BD3-B62E-D70ABF153AE5}">Red Team</asp:ListItem>
    <asp:ListItem value="{DEFB7DA6-B0FF-4C36-A015-F3E8BC7AECA2}">Yellow Team</asp:ListItem>
    <asp:ListItem value="{D37EFA0C-988A-4A2A-8D6E-80E3BAE00DEE},{7543E282-C9B8-435A-86A2-70E8E3BB38E5},{F6BEF34A-215E-4179-9F4C-68F7C43D755F},{D50AD44A-686A-4BD3-B62E-D70ABF153AE5},{DEFB7DA6-B0FF-4C36-A015-F3E8BC7AECA2}">All Teams</asp:ListItem>
</asp:DropDownList>
<asp:Button runat="server" Text="Submit" />

---

private void Page_Load(object sender, EventArgs e)
{
    if (!String.IsNullOrEmpty(ParticipantsSelectList.SelectedValue)) // SelectedValue is always empty string (value of the first item in the list)
    {
        resultsPanel.Visible = true;
        selectTeamLabel.Visible = false;
        GenerateResultsTable();
    }
    else
    {
        resultsPanel.Visible = false;
        selectTeamLabel.Visible = true;
    }
}

Answer 1

尝试在Page_Load 中使用!Page.IsPostBack

private void Page_Load(object sender, EventArgs e)
{

    if (!Page.IsPostBack)
    { 
        //Your Code....
    }
}