Understanding ASP.NET Eval() and Bind()

asp.net, bind, eval

Solution

For read-only controls they are the same. For 2 way databinding, using a datasource in which you want to update, insert, etc with declarative databinding, you'll need to use `Bind`.

Imagine for example a GridView with a `ItemTemplate` and `EditItemTemplate`. If you use `Bind` or `Eval` in the `ItemTemplate`, there will be no difference. If you use `Eval` in the `EditItemTemplate`, the value will not be able to be passed to the `Update` method of the `DataSource` that the grid is bound to.

UPDATE: I've come up with this example:

<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Data binding demo</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:GridView 
            ID="grdTest" 
            runat="server" 
            AutoGenerateEditButton="true" 
            AutoGenerateColumns="false" 
            DataSourceID="mySource">
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <%# Eval("Name") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox 
                            ID="edtName" 
                            runat="server" 
                            Text='<%# Bind("Name") %>' 
                        />
                    </EditItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
    </form>

    <asp:ObjectDataSource 
        ID="mySource" 
        runat="server"
        SelectMethod="Select" 
        UpdateMethod="Update" 
        TypeName="MyCompany.CustomDataSource" />
</body>
</html>

And here's the definition of a custom class that serves as object data source:

public class CustomDataSource
{
    public class Model
    {
        public string Name { get; set; }
    }

    public IEnumerable<Model> Select()
    {
        return new[] 
        {
            new Model { Name = "some value" }
        };
    }

    public void Update(string Name)
    {
        // This method will be called if you used Bind for the TextBox
        // and you will be able to get the new name and update the
        // data source accordingly
    }

    public void Update()
    {
        // This method will be called if you used Eval for the TextBox
        // and you will not be able to get the new name that the user
        // entered
    }
}

Problem

Can anyone show me some absolutely minimal ASP.NET code to understand `Eval()` and `Bind()`? It is best if you provide me with two separate code-snippets or may be web-links.

Original source