Control in UpdatePanel loses value

问题

I have two comboboxes, first one triggers updatepanel that updates second one:

        protected void cb1_SelectedIndexChanged(object sender, EventArgs e)
        {

        cb2.DataSource = DT1;
        cb2.DataBind();


         }

Problem is, when I click button, all values are ok, except one in UpdatePanel, so updatepanel somehow resets selected index on child controls.

Any idea how to fix this?

I know about sessions, but I don't know on what step to assign value of cb2 to session.

Thanks.

Update, aspx

    <asp:UpdatePanel ID="UpdatePanel1" runat="server" ChildrenAsTriggers="False" 
                                                        UpdateMode="Conditional">
    <dx:ASPxComboBox ID="cb2" runat="server" Height="22px" ValueField="ID" 
                                                                ValueType="System.Int32" Width="170px">
                                                                <Columns>
                                                                    <dx:ListBoxColumn Caption="ID" FieldName="ID" Visible="False" />
                                                                    <dx:ListBoxColumn Caption="City" FieldName="City" />
                                                                </Columns>
                                                            </dx:ASPxComboBox>
</ContentTemplate>
                                                    <Triggers>
                                                        <asp:AsyncPostBackTrigger
    ControlID="cb1" EventName="SelectedIndexChanged" />
                                                        </Triggers>
                                                    </asp:UpdatePanel>

回答1:

A couple of things here: you have ChildrenAsTriggers="False", but yet you have an async postback trigeer for a child control: 'cb2'. I think you should remove the ChildrenAsTriggers="False" property ("true" is default value) and you probably meant to have the ansync postback trigeer set to the `cb1' control like below:

   <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"> 
    <ContentTemplate>
      <dx:ASPxComboBox ID="cb2" runat="server" Height="22px" ValueField="ID"     
                       ValueType="System.Int32" Width="170px">  
        <Columns>
           <dx:ListBoxColumn Caption="ID" FieldName="ID" Visible="False" /> 
           <dx:ListBoxColumn Caption="City" FieldName="City" /> 
        </Columns>                                                             
    </dx:ASPxComboBox> 
   </ContentTemplate>                                                     
   <Triggers>                                                         
     <asp:AsyncPostBackTrigger ControlID="cb1" EventName="SelectedIndexChanged" />   
   </Triggers>                                                     
  </asp:UpdatePanel>

Also I think your original code copied was missing the opening <ContentTemplate> tag.

At this point your cb1 control's event `cb1_SelectedIndexChanged' should fire and be able to update the cb2 control's datasource in the UpdatePanel above.

来源：https://stackoverflow.com/questions/9911816/control-in-updatepanel-loses-value

标签

ASP.NET

updatepanel