Question

I am working on a metrics screen that will display several charts based on different groups in a database. Part of it uses a function that hides selected charts until the user clicks to display them.

The problem is this: I’m using a Databind on the dropdownlist, so every time I select a new group, the page refreshes and everything returns to its default state.

My question is this: Is there a way that I can avoid refreshing the page every time I select a new option from the dropdown list? If so, how? If not, is there a better way to create the dropdownlist and attach values to it? If I set AppendDataBoundItems to false, then I always get the selected value as the first item in the list.

Here’s my code for the dropdownlist:

    <asp:DropDownList ID="MinistryDropdown" OnSelectedIndexChanged="Selection_Change" AutoPostback="true" AppendDataBoundItems="true" runat="server"/>

Then C# code behind it is this:

public void Page_Load(object sender, EventArgs e){
    MinistryDropdown.DataSource = CreateDataSource();
    MinistryDropdown.DataTextField = "Description";
    MinistryDropdown.DataValueField = "Description";
    MinistryDropdown.DataBind();

...other code here...
}
ICollection CreateDataSource(){
    DataTable Ministries = new DataTable();

    Ministries = oDatabase.GetData(@"SELECT DISTINCT B.Description
        FROM tblInvolvement AS A LEFT JOIN tblMinistries AS B
        ON A.Activity = B.MinistryID");

    DataView dv = new DataView(Ministries);
    return dv;
}

Answer 1

Try to use the ASP.NET UpdatePanel. Just wrap your DropDownList in it, and it should works. Here is a quick example that I didn’t test.

<asp:ScriptManager ID="ScriptManager" runat="server"></asp:ScriptManager>
<asp:UpdatePanel runat="server" UpdateMode="Conditional">
    <ContentTemplate>
       <asp:DropDownList ID="MinistryDropdown" OnSelectedIndexChanged="Selection_Change" AutoPostback="true" AppendDataBoundItems="true" runat="server"/>
    </ContentTemplate>
</asp:UpdatePanel>

On a final note, you will soon find out the limits of this solution, and later you might prefer to use Javascript instead.