Add empty item to dropdownlist of custom objects in C#

Question

We are binding a list of custom objects to an ASP.NET DropDownList in C# but we want to allow for the DropDownList to not have anything selected initially. One way of doing

Answer 1

You could add to the databound event:

protected void DropDownList1_DataBound(object sender, EventArgs e)
        {
            DropDownList1.Items.Insert(0,new ListItem("",""));
        }

Answer 2

First:

DropDownList1.Items.Clear();

Then add listItems to the dropDownList.

This prevents the dropDownList from acquiring an ever increasing list of items every time it is rendered in a postback or asynchronous postback.

Answer 3

Yes, create your list like so:

<asp:DropDownList ID="Whatever" runat="server" AppendDataBoundItems="True">
    <asp:ListItem Value="" Text="Select one..." />
</asp:DropDownList>

(Note the use of AppendDataBoundItems="True")

And then when you bind, the bound items are put after the empty item rather than replacing it.

Answer 4

Just working on this actually, here's what I got so far (along with a couple databinding goodies)

public interface ICanBindToObjectsKeyValuePair {
    void BindToProperties<TYPE_TO_BIND_TO>(IEnumerable<TYPE_TO_BIND_TO> bindableEnumerable, Expression<Func<TYPE_TO_BIND_TO, object>> textProperty, Expression<Func<TYPE_TO_BIND_TO, object>> valueProperty);
}

public class EasyBinderDropDown : DropDownList, ICanBindToObjectsKeyValuePair {
    public EasyBinderDropDown() {
        base.AppendDataBoundItems = true;
    }
    public void BindToProperties<TYPE_TO_BIND_TO>(IEnumerable<TYPE_TO_BIND_TO> bindableEnumerable,
        Expression<Func<TYPE_TO_BIND_TO, object>> textProperty, Expression<Func<TYPE_TO_BIND_TO, object>> valueProperty) {
        if (ShowSelectionPrompt)
            Items.Add(new ListItem(SelectionPromptText, SelectionPromptValue));
        base.DataTextField = textProperty.MemberName();
        base.DataValueField = valueProperty.MemberName();
        base.DataSource = bindableEnumerable;
        base.DataBind();
    }
    public bool ShowSelectionPrompt { get; set; }
    public string SelectionPromptText { get; set; }
    public string SelectionPromptValue { get; set; }
    public virtual IEnumerable<ListItem> ListItems {
        get { return Items.Cast<ListItem>(); }
    }
}

Notice one thing that you can do is

dropDown.BindToProperties(myCustomers, c=>c.CustomerName, c=>c.Id);