Dropdownlist in repeater update panel losing value after postback - asp.net

Question

Dear all i have the following dropdownlist which is inside an update panel inside a repeater.
<asp:Repeater OnItemDataBound="rprProperties_ItemDataBound" ID="rprProperties" runat="server">
<ItemTemplate>
<div class="mb-2">
<asp:Label style="width : 100px;float:left;" ID="Label1" runat="server" Text='<%# Container.DataItem("name") %>'></asp:Label>
<asp:Label style="width : 100px;float:left;" ID="propID" runat="server" Text='<%# Container.DataItem("id") %>' Visible="false"></asp:Label>
<asp:UpdatePanel ID="UpdatePanel2" runat="server">
<ContentTemplate>
<asp:DropDownList ClientIDMode="AutoID" AutoPostBack="true" OnSelectedIndexChanged="ddlProperty_SelectedIndexChanged" style="width:100px" CssClass="filter-dropdown bg-light" DataValueField="id" DataTextField="name" ID='ddlProperty' runat="server"></asp:DropDownList>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</ItemTemplate>
</asp:Repeater>
i'm populating the ddl with this code in the ItemDataBound event of the repeater.
Dim propID As Label = TryCast(e.Item.FindControl("propID"), Label)
Dim ddl As DropDownList = TryCast(e.Item.FindControl("ddlProperty"), DropDownList)
Dim varDbconn As New SqlConnection(ConfigurationManager.ConnectionStrings("shopCS").ToString)
Dim varDbcomm As SqlCommand
Dim varDbRead As SqlDataReader
varDbconn.Open()
varDbcomm = New SqlCommand("exec spShowItemPropValues #property,#id,#lang ", varDbconn)
varDbcomm.Parameters.AddWithValue("#property", SqlDbType.Int).Value = propID.Text
varDbcomm.Parameters.AddWithValue("#id", SqlDbType.Int).Value = Request.QueryString("id")
varDbcomm.Parameters.AddWithValue("#lang", SqlDbType.NVarChar).Value = Session("lang")
varDbRead = varDbcomm.ExecuteReader()
Dim varDt As New DataTable
varDt.Load(varDbRead)
ddl.DataSource = varDt
ddl.DataBind()
varDbcomm.Dispose()
varDbRead.Close()
varDbconn.Close()
when i select a value, the dropdownlist resets to the first item in the dropdownlist instead of keeping the selected value.
i want to retain that value.
thanks.

Answer 1

You forgot to add the AsyncPostBackTrigger. Put it before </UpdatePanel>
<asp:Repeater OnItemDataBound="rprProperties_ItemDataBound" ID="rprProperties" runat="server">
<ItemTemplate>
<div class="mb-2">
<asp:Label style="width : 100px;float:left;" ID="Label1" runat="server" Text='<%# Container.DataItem("name") %>'></asp:Label>
<asp:Label style="width : 100px;float:left;" ID="propID" runat="server" Text='<%# Container.DataItem("id") %>' Visible="false"></asp:Label>
<asp:UpdatePanel ID="UpdatePanel2" runat="server">
<ContentTemplate>
<asp:DropDownList ClientIDMode="AutoID" AutoPostBack="true" OnSelectedIndexChanged="ddlProperty_SelectedIndexChanged" style="width:100px" CssClass="filter-dropdown bg-light" DataValueField="id" DataTextField="name" ID='ddlProperty' runat="server">
</asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ddlProperty" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
</ItemTemplate>
</asp:Repeater>