How to get the previous item on DropDownList before OnSelectedIndexChanged fires the event

Question

How would I get the previous item on DropDownList before OnSelectedIndexChanged fires the event?

Example: I had a DropDownList that has names as its items ("John", "Mark"). By default the SelectedIndex is "John". Upon changing its index and selecting "Mark" the event OnSelectedIndexChanged will be triggered. When I use ddlName.SelectedIndex it will return only the index for "Mark" which I want to get is the index of "John".

Answer 1

You can't capture an event prior to the change, but you could easily store the previous value in a variable. Each time SelectedIndexChanged is fired, use the previous value and then set it to the new index (for the next time the event fires). To handle the case when it's a new selection (from the default), you can either set the variable when the page loads, or allow it to be null and have that alert you to the fact it's a new selection (which you can then handle however you like).

Answer 2

<asp:DropDownList ID="ddlName" runat="server" AutoPostBack="true" 
        onselectedindexchanged="ddlName_SelectedIndexChanged">
        <asp:ListItem Text="John" Value="1"></asp:ListItem>
        <asp:ListItem Text="Mark" Value="2"></asp:ListItem>
        <asp:ListItem Text="Jim" Value="3"></asp:ListItem>
    </asp:DropDownList>

.cs file code here:

public static int PreviousIndex;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                ddlName.AppendDataBoundItems = true;
                ddlName.Items.Add(new ListItem("Other", "4"));
                PreviousIndex = ddlName.SelectedIndex;
            }

        }

        protected void ddlName_SelectedIndexChanged(object sender, EventArgs e)
        {
            string GetPreviousValue = ddlName.Items[PreviousIndex].Text;
            Response.Write("This is Previously Selected Value"+ GetPreviousValue);
            //Do selected change event here.

            PreviousIndex = ddlName.SelectedIndex;

        }

Answer 3

You could use the e.OldValues property.

<asp:DropDownList ID="esDropDownList" runat="server" DataSourceID="SqlDataSourceddlEnrolmentStatus" DataTextField="EnrolmentStatusDescription" DataValueField="EnrolmentStatusID" SelectedValue='<%# Bind("StudentEnrolmentStatus") %>'>
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSourceddlEnrolmentStatus" runat="server"
ConnectionString="<%$ ConnectionStrings:ATCNTV1ConnectionString %>" SelectCommand="SELECT [EnrolmentStatusID], [EnrolmentStatusDescription] FROM [tblEnrolmentStatuses] ORDER BY [EnrolmentStatusID]">
</asp:SqlDataSource>

And in code behind (assuming your dropdownlist is in a formview) ...

    protected void FormView1_ItemUpdated(object sender, FormViewUpdatedEventArgs e)
    {
..
            String msg = "This is the new value " + e.NewValues["StudentEnrolmentStatus"].ToString()+ " and this is the old value " + e.OldValues["StudentEnrolmentStatus"].ToString();
..
    }