Question

I have a GridView with a DropDownList in each row. (The items in the DropDownList are the same for each.) I have a DropDownList “ddlView” outside of the GridView that is used for filtering the available options in the other DropDownLists. The default selection for ddlView is no filter.

When a user selects a new value for ddlView any selected values in the other DropDownLists disappear if they are not one of the values present after the filter is applied. What I would like to happen in that case is the previously selected value still be present and selected.

What is the best way to accomplish this?

The previously selected values are available during postback but appear to be cleared once DataBind() is called on the GridView, so I am unable to determine their previous value in the method where they are populated (the RowDataBound event).

My best idea so far is to manually store that information into an object or collection during postback and reference it later during the databinding events.

Is there a better way?

Answer 1

I don’t think there is a better way to accomplish this as when the GridView is bound all of the controls are recreated thus removing the selections.

The following works: (I store the selections on postback to retrieve again in the RowDataBound event)

Markup

<asp:Button ID="button1" runat="server" Text="Post Back" OnClick="button1_Click" />
<br />
<asp:GridView ID="gridView1" runat="server">
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:DropDownList ID="gridViewDropDownList" runat="server">
                    <asp:ListItem Value="1">Item 1</asp:ListItem>
                    <asp:ListItem Value="2">Item 2</asp:ListItem>
                    <asp:ListItem Value="3">Item 3</asp:ListItem>
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Code

public class GridViewDropDownSelections
{
    public int RowIndex { get; set; }
    public int SelectedIndex { get; set; }
}

...

private List<GridViewDropDownSelections> selectedDropDownListItems = new List<GridViewDropDownSelections>();

protected override void OnLoad(EventArgs e)
{
    var selections = gridView1.Rows.Cast<GridViewRow>().Where(r => r.RowType == DataControlRowType.DataRow)
        .Select(r => new GridViewDropDownSelections() { RowIndex = r.RowIndex, SelectedIndex = ((DropDownList)r.FindControl("gridViewDropDownList")).SelectedIndex }).ToList();

    selectedDropDownListItems.AddRange(selections);

    gridView1.RowDataBound += new GridViewRowEventHandler(gridView1_RowDataBound);

    if (!IsPostBack)
    {
        BindDataGrid();
    }

    base.OnLoad(e);
}

protected void button1_Click(object sender, EventArgs e)
{
    BindDataGrid();
}

private void BindDataGrid()
{
    //Dummy data
    string[] data = new string[] { "Item 1", "Item 2", "Item 3" };
    gridView1.DataSource = data;
    gridView1.DataBind();
}

void gridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        var selection = selectedDropDownListItems.FirstOrDefault(i => i.RowIndex == e.Row.RowIndex);
        if (selection != null)
        {
            try
            {
                DropDownList gridViewDropDownList = (DropDownList)e.Row.FindControl("gridViewDropDownList");
                gridViewDropDownList.SelectedIndex = selection.SelectedIndex;
            }
            catch (Exception)
            {
            }
        }
    }
}

Hope it helps.