Question

How to make a dynamic dropdownlist on asp.net?

I have a dropdownlist:

<asp:DropDownList ID="FirstParameter" runat="server">
    <asp:ListItem Value="1">1</asp:ListItem>
    <asp:ListItem Value="2">2</asp:ListItem>
    <asp:ListItem Value="3">3</asp:ListItem>
</asp:DropDownList>  

A label and the other dropdownlist:

<asp:Label ID="SecondParameter_Label" runat="server" Text=""></asp:Label>

<asp:DropDownList ID="SecondParameter" runat="server">
</asp:DropDownList> 

When I change the selection on the FirstParameter dropdownlist, then the text on SecondParameter_Label should change based on the selection, and so for the SecondParameter dropdownlist, should be binding with the data filter based on the selected value on the first dropdownlist.

I have tried this code but it doesn’t work:

Protected Sub FirstParameter_SelectedIndexChanged(sender As Object, e As System.EventArgs) Handles FirstParameter.SelectedIndexChanged
    'Change the label text
    SecondParameter_Label.Text = ReportType_Dropdownlist.SelectedItem.Value

    'Bind value to the SecondParameter dropdownlist
    SecondParameter.DataSource = dataTableName '--> Assumed that I already have the DataTable called from a class
    SecondParameter.DataTextField = "NameofDatabaseColumn"
    SecondParameter.DataValueField = "NameofDatabaseColumn"
    SecondParameter.DataBind()
End Sub

I have tried to change the SecondParameter_Label text first but still doesn’t work. How can I do that?

Answer 1

Try adding AutoPostBack property to the dropdowns. You will also need to handle them on the server side. Your first dropdown should like this:

<asp:DropDownList ID="FirstParameter" runat="server" AutoPostBack="true">
    <asp:ListItem Value="1">1</asp:ListItem>
    <asp:ListItem Value="2">2</asp:ListItem>
    <asp:ListItem Value="3">3</asp:ListItem>
</asp:DropDownList>