DropDownList所选项目总是列表中的第一项

Question

我在用户控件中有一个DropDownList;然而，无论我做什么，我都无法获得任何“选定”属性（SelectedItem，SelectedIndex，SelectedValue）以正确填充。所有这三个属性的值都是我列表中的第一个项目，不管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

尝试使用!Page.IsPostBack在Page_Load

private void Page_Load(object sender, EventArgs e) 
{ 

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