获取查询结果两次

Question

嗨 我在本页获得两次结果，我不知道为什么。在我选择DropdownList1中的选项2后，当我查询数据库时，结果出现两次。是否因为结果出现在更新面板中？非常感谢您的帮助。我真的不能看到代码的问题，它让我发疯了！

page.aspx

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"> 
<asp:ListItem Value="Select">Select</asp:ListItem> 
<asp:ListItem value="Option 1">Option 1</asp:ListItem> 
    <asp:ListItem Value="Option 2">Option 2</asp:ListItem> 
</asp:DropDownList> 


    <asp:UpdatePanel id="FirstPanel" runat="server" RenderMode="Inline"> 
    <ContentTemplate> 
     <div id="tohide1" visible="False" runat="server"> 
      +++Do something+++ 
      </div> 

<div id="tohide2" visible="false" runat="server"> 
    <asp:Label ID="Label1" runat="server"></asp:Label> 
    </div> 

    </ContentTemplate> 
    <Triggers> 
    <asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged"></asp:AsyncPostBackTrigger> 
    </Triggers> 
    </asp:UpdatePanel> 

page.aspx.vb

Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged 
    If DropDownList1.SelectedValue = "Option 1" Then 

     tohide1.Visible = "True" 
     tohide2.Visible = "False" 

    ElseIf DropDownList1.SelectedValue = "Option 2" Then 

     tohide1.Visible = "False" 
     tohide2.Visible = "True" 

    Dim connectionString As String = ConfigurationManager.ConnectionStrings("myConnString").ToString() 
     Dim SqlQuery As String 

     SqlQuery = "SELECT CourseCode, Q1 FROM Courses WHERE (Q1 = 1)" 

     Dim conn As SqlConnection = New SqlConnection(connectionString) 
     Dim Cmd1 As SqlCommand = New SqlCommand(SqlQuery, conn) 

     Try 
      conn.Open() 

      Dim myReader As SqlDataReader = Cmd1.ExecuteReader 


      While myReader.Read() 

       Dim CourseCode As String = myReader("CourseCode") 

       Label1.Text += CourseCode & "<br />" 

      End While 

     Catch ex As SqlException 
      lblmessage.Text = ex.Message() 
     Finally 
      conn.Close() 
     End Try 

    End If 
End Sub 

Answer 1

我会重置Label1.Text到附近的 “” 程序的顶部。这应该可以阻止结果中的重复。