Dynamically adding rows to ASP.NET repeater in reaction to event

Question

I am trying to create ASP.NET server control (pure code, without ascx template - because control must be completly contained in .dll and it must not rely on external .ascx files), and I have a problem with dynamically adding items to repeater.

I want to add item to repeater in reaction to SelectedIndexChanged event, but when i do second DataBind() in that event, i lose data from ViewModel (for example, textboxes contains default data instead of text entered by user).

Simplified version of my code (in large portion borrowed from MS composite control example - http://msdn.microsoft.com/en-us/library/3257x3ea%28v=vs.100%29.aspx):

[ToolboxData("<{0}:FilterControl runat=server />")]
public class FilterControl : CompositeControl, IPostBackDataHandler
{
    private List<FilteringProperty> elements = new List<FilteringProperty>();
    private DropDownList filteringElementsDropDownList;
    private Repeater usedFiltersRepeater;

    [Bindable(true), DefaultValue(null), Description("Active filters")]
    public List<FilteringProperty> UsedElements
    {
        get
        {
            EnsureChildControls();
            if (ViewState["UsedElements"] == null)
            {
                ViewState["UsedElements"] = new List<FilteringProperty>();
            }
            return (List<FilteringProperty>)ViewState["UsedElements"];
        }
        set
        {
            EnsureChildControls();
            ViewState["UsedElements"] = value;
        }
    }

    protected override void RecreateChildControls()
    {
        EnsureChildControls();
    }

    protected override void CreateChildControls()
    {
        Controls.Clear();

        filteringElementsDropDownList = new DropDownList { AutoPostBack = true };
        usedFiltersRepeater = new Repeater();

        foreach (var element in elements)
        {
            filteringElementsDropDownList.Items.Add(new ListItem(element.DisplayName));
        }

        filteringElementsDropDownList.SelectedIndexChanged += (sender, e) =>
        {
            string selectedText = filteringElementsDropDownList.SelectedValue;
            FilteringProperty condition = elements.First(x => x.DisplayName == selectedText);

            var toRemove = filteringElementsDropDownList.Items.Cast<ListItem>().FirstOrDefault(x => x.Text == condition.DisplayName);
            if (toRemove != null)
            {
                filteringElementsDropDownList.Items.Remove(toRemove);
            }

            UsedElements.Add(condition);
            // ======> A <========
        };

        usedFiltersRepeater.ItemDataBound += (sender, args) =>
        {
            FilteringProperty dataItem = (FilteringProperty)args.Item.DataItem;

            Control template = args.Item.Controls[0];
            TextBox control = (TextBox)template.FindControl("conditionControl");
            control.Text = dataItem.DisplayName;
            // ======> C <========
        };

        usedFiltersRepeater.ItemTemplate = // item template
        usedFiltersRepeater.DataSource = UsedElements;
        usedFiltersRepeater.DataBind();
        // ======> B <========

        Controls.Add(filteringElementsDropDownList);
        Controls.Add(usedFiltersRepeater);
    }
}

I marked important portions of code with (A), (B) and (C)

The problem is, (A) is executed after DataBinding (B and C), so changes in UsedElements are not visible until next postback.

It is possible to add usedFiltersRepeater.DataBind(); after (A), but than all controls are recreated without data from viewstate (i.e empty)

Is there a way to dynamically change repeater after databinding, such that data of contained controls is preserved?

Tl;dr - i have a DropDownList and I want to add editable items to Repeater on SelectedIndexChanged (without losing viewstate).

Answer 1

I finally solved my problem. My solution is rather dirty, but it seems to work fine.

Instead of simple databinding:

• I get state from all controls in repeater and save it in temporary variable (state for each control includes everything, such as selected index for dropdownlists) using my function GetState()
• modify this state in any way i want
• restore full state using my function SetState()

For example:

FilterState state = GetState();
state.Conditions.Add(new ConditionState { Item = condition });
SetState(state);