[asp.net] Understanding ASP.NET Eval() and Bind()

The question was answered perfectly by Darin Dimitrov, but since ASP.NET 4.5, there is now a better way to set up these bindings to replace* Eval() and Bind(), taking advantage of the strongly-typed bindings.

*Note: this will only work if you're not using a SqlDataSource or an anonymous object. It requires a Strongly-typed object (from an EF model or any other class).

This code snippet shows how Eval and Bind would be used for a ListView control (InsertItem needs Bind, as explained by Darin Dimitrov above, and ItemTemplate is read-only (hence they're labels), so just needs an Eval):

<asp:ListView ID="ListView1" runat="server" DataKeyNames="Id" InsertItemPosition="LastItem" SelectMethod="ListView1_GetData" InsertMethod="ListView1_InsertItem" DeleteMethod="ListView1_DeleteItem">
    <InsertItemTemplate>
        <li>
            Title: <asp:TextBox ID="Title" runat="server" Text='<%# Bind("Title") %>'/><br />         
            Description: <asp:TextBox ID="Description" runat="server" TextMode="MultiLine" Text='<%# Bind("Description") %>' /><br />        
            <asp:Button ID="InsertButton" runat="server" Text="Insert" CommandName="Insert" />        
        </li>
    </InsertItemTemplate>
    <ItemTemplate>
        <li>
            Title: <asp:Label ID="Title" runat="server" Text='<%#  Eval("Title") %>' /><br />
            Description: <asp:Label ID="Description" runat="server" Text='<%# Eval("Description") %>' /><br />        
            <asp:Button ID="DeleteButton" runat="server" Text="Delete" CommandName="Delete" CausesValidation="false"/>
        </li>
      </ItemTemplate>

From ASP.NET 4.5+, data-bound controls have been extended with a new property ItemType, which points to the type of object you're assigning to its data source.

<asp:ListView ItemType="Picture" ID="ListView1" runat="server" ...>

Picture is the strongly type object (from EF model). We then replace:

Bind(property) -> BindItem.property
Eval(property) -> Item.property

So this:

<%# Bind("Title") %>      
<%# Bind("Description") %>         
<%#  Eval("Title") %> 
<%# Eval("Description") %>

Would become this:

<%# BindItem.Title %>         
<%# BindItem.Description %>
<%# Item.Title %>
<%# Item.Description %>

Advantages over Eval & Bind:

• IntelliSense can find the correct property of the object your're working with
• If property is renamed/deleted, you will get an error before page is viewed in browser
• External tools (requires full versions of VS) will correctly rename item in markup when you rename a property on your object

Source: from this excellent book