如何向此ASP.NET DropDownList控件添加默认的“选择”选项？

Question

I am a new ASP.NET developer and I am trying to learn Linq-To-Entities. I am trying to bind a DropDownList with the Linq statement for retrieving the list of status in the Status Entity. Everything is working fine. However, I am trying now to add "Select" option to the DropDownList but It doesn't work with me. Could you please tell me how to fix this?

ASP.NET Code:

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
                OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">

Code-Behind:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DropDownList1.Items.Add(new ListItem("Select", "0", true));
            bindStatusDropDownList();
        }
    }

private void bindStatusDropDownList()
    {
        Status status = new Status();
        DropDownList1.DataSource = status.getData();
        DropDownList1.DataValueField = "ID";
        DropDownList1.DataTextField = "Description";
        DropDownList1.DataBind();
    }

UPDATE:

I also tried to do in the markup set of the DropDownList but it did not work too with me

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
                OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
                    <asp:ListItem Selected="True" Value="0" Text="Select"></asp:ListItem>
            </asp:DropDownList>

Answer 1

The reason it is not working is because you are adding an item to the list and then overriding the whole list with a new DataSource which will clear and re-populate your list, losing the first manually added item.

So, you need to do this in reverse like this:

Status status = new Status();
DropDownList1.DataSource = status.getData();
DropDownList1.DataValueField = "ID";
DropDownList1.DataTextField = "Description";
DropDownList1.DataBind();

// Then add your first item
DropDownList1.Items.Insert(0, "Select");

Answer 2

Although it is quite an old question, another approach is to change AppendDataBoundItems property. So the code will be:

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
                  OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"
                  AppendDataBoundItems="True">
     <asp:ListItem Selected="True" Value="0" Text="Select"></asp:ListItem>
</asp:DropDownList>

Answer 3

I have tried with following code. it's working for me fine

ManageOrder Order = new ManageOrder();
Organization.DataSource = Order.getAllOrganization(Session["userID"].ToString());
Organization.DataValueField = "OrganisationID";
Organization.DataTextField = "OrganisationName";                
Organization.DataBind();                
Organization.Items.Insert(0, new ListItem("Select Organisation", "0"));

Answer 4

Move DropDownList1.Items.Add(new ListItem("Select", "0", true)); After bindStatusDropDownList();

so:

    if (!IsPostBack)
    {
        bindStatusDropDownList(); //first create structure
        DropDownList1.Items.Add(new ListItem("Select", "0", true)); // after add item
    }

Answer 5

If you do an "Add" it will add it to the bottom of the list. You need to do an "Insert" if you want the item added to the top of the list.

Answer 6

Private Sub YourWebPage_PreRenderComplete(sender As Object, e As EventArgs) Handles Me.PreRenderComplete

     If Not IsPostBack Then
     DropDownList1.Items.Insert(0, "Select")
     End If

End Sub

Answer 7

If you want to make the first item unselectable, try this:

DropDownList1.Items.Insert(0, new ListItem("Select", "-1"));
DropDownList1.Items[0].Attributes.Add("disabled", "disabled");