Manually insert an item into a ListView control

Question

I have searched S/O and google, but I can't figure this out (most of the search results as populating a Listview from a datasource). I want to add an item to a listview control manually, based on user selection.

ListView listView1 = new ListView();
listView1.Items.Add(lstAuthors[i]);  

I get an error:
The best overloaded method match for 'System.Collections.Generic.ICollection.Add(System.Web.UI.WebControls.ListViewDataItem)' has some invalid arguments

What is causing the error?

Answer 1

This error simply means that lstAuthors[i] is not a System.Web.UI.WebControls.ListViewDataItem (which is the only valid parameter for the ListView.Items.Add function.

In order to do this the way you are doing it now, you would need to initialize a ListViewDataItem , and use dummy values for the dataIndex parameter (since you don't have an underlying indexed datasource):

ListViewDataItem newItem = new ListViewDataItem(dataIndex, displayIndex);

To be honest, this doesn't really seem like the right way to use the ListView control. Maybe you could tell us what you're trying to accomplish, and we could help out with another approach.

---

Here is a really trimmed down, basic approach to doing what you would like to do. You basically maintain a generic List<T> as your datasource, and bind that to your ListView . This way you can handle all of the details of maintaining the contents of your ListView, but you can still use the built in power of the databinding.

Basic markup (a ListView with one item in it's ItemTemplate, a DropDownList to select items from, and a Button for adding those items to the ListView):

<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
    <asp:ListView ID="ListView1" runat="server">
        <ItemTemplate>
            <div>
                <asp:Label ID="AuthorNameLbl" runat="server" Text='<%# Eval("AuthorName") %>'></asp:Label>
            </div>
        </ItemTemplate>
    </asp:ListView>
    <br />
    <asp:DropDownList ID="DropDownList1" runat="server">
        <asp:ListItem>Stephen King</asp:ListItem>
        <asp:ListItem>Mary Shelley</asp:ListItem>
        <asp:ListItem>Dean Koontz</asp:ListItem>
    </asp:DropDownList>
    <br />
    <br />
    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
</asp:Content>

And code-behind:

// Honestly, this string  just helps me avoid typos when 
// referencing the session variable
string authorKey = "authors";

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        // If the session variable is empty, initialize an 
        // empty list as the datasource
        if (Session[authorKey] == null)
        {
            Session[authorKey] = new List<Author>();
        }
        BindList();
    }
}

protected void Button1_Click(object sender, EventArgs e)
{
    // Grab the current list from the session and add the 
    // currently selected DropDown item to it.
    List<Author> authors = (List<Author>)Session[authorKey];
    authors.Add(new Author(DropDownList1.SelectedValue));
    BindList();
}

private void BindList()
{
    ListView1.DataSource = (List<Author>)Session[authorKey];
    ListView1.DataBind();
}

// Basic author object, used for databinding
private class Author
{
    public String AuthorName { get; set; }

    public Author(string name)
    {
        AuthorName = name;
    }
}