Programmatic DataBinding in Asp.Net

An alternative to declarative databinding, you can programmatically bind any of the List controls to a data source

Example:

Lets create a BulletList which shows the list of Fruits.

<asp:BulletedList

            ID="blFruits"

            runat="server" />

And in Page_Load() event write this code. 

protected void Page_Load(object sender, EventArgs e)

    {

        if (!IsPostBack)

        {

            List<String> fruits = new List<string>();

            fruits.Add("Apple");

            fruits.Add("Banana");

            fruits.Add("Mango");

            blFruits.DataSource = fruits;

            blFruits.DataBind();

        }

    }

if(!IsPostBack) prevents the re-initialisation of the BulletList items during postbacks.

Read About Declarative DataBinding : Declarative DataBinding in Asp.Net

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Declarative DataBinding in Asp.Net

You can bind any of the List controls to a data source. The List controls support both

declarative databinding and programmatic databinding

Example:

Suppose you have a movies table in your database. It has two columns named Id and Title.

<asp:DropDownList

            ID="ddlMovies"

            DataSourceID="srcMovies"

            DataTextField="Title"

            DataValueField="Id"

            runat="server" />

        <asp:SqlDataSource

            ID="srcMovies"

            SelectCommand="SELECT Id, Title FROM Movies"

            ConnectionString="yourConnectionString"

            runat="server" />

The DropDownList control’s DataSourceID property points to the ID of the SqlDataSource control. The SqlDataSource control retrieves the records from the Movies database table. The DropDownList control grabs these records from the SqlDataSource control and creates a ListItem control for each data item. 

The DropDownList control has both its DataTextField and DataValueField properties set. When the DropDownList control creates each of its list items, it uses the values of the DataTextField and DataValueField properties to set the Text and Value properties of each list item.

Read About Programmatic DataBinding :  ProgrammaticDataBinding in Asp.Net

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Eval() and Bind() Two-Way DataBinding Expressions in Asp.Net

The ASP.NET Framework supports both one-way DataBinding expressions and two-way DataBinding expressions.

In a oneway DataBinding expression, you use the DataBinding expression to display the value of a data item. You use the Eval() method to display the value of a one-way DataBinding expression.

In a two-way DataBinding expression, you not only can display the value of a data item,
you also can modify the value of a data item. You use the Bind() method when working with a    two-way DataBinding expression.

Example:

Suppose you have a movies table in your database. It has columns named Id, Title, Director, DateReleased.

<asp:FormView id="FormView1" DataKeyNames="Id" DataSourceId="srcMovies" DefaultMode="Edit" AllowPaging="true" Runat="server">
<EditItemTemplate>

<asp:Label
id="lblTitle"
Text="Title:"
AssociatedControlID="txtTitle"
Runat="server" />

<asp:TextBox
id="txtTitle"
Text='<%#Bind(“Title")%>'
Runat="server" />
<br />

<asp:Label
id="lblDirector"
Text="Director:"
AssociatedControlID="txtDirector"
Runat="server" />

<asp:TextBox
id="txtDirector"
Text='<%#Bind(“Director")%>'
Runat="server" />
<br />

<asp:Button
id="btnUpdate"
Text="Update"
CommandName="Update"
Runat="server" />
</EditItemTemplate>
</asp:FormView>

<asp:SqlDataSource id="srcMovies" ConnectionString="yourConnectionString"
SelectCommand="SELECT Id, Title,Director,DateReleased FROM Movies"
UpdateCommand="UPDATE Movies SET Title=@Title,
Director=@Director WHERE Id=@Id"
Runat="server" />

The FormView contains an EditItemTemplate. The EditItemTemplate contains three TextBox controls. Each TextBox control has a two-way DataBinding expression assigned to its Text property.

The DataBinding expressions associate the TextBox control properties with the properties of the data item being edited. When you click the Update button, any changes you make to the Text properties are updated in the Movies database table.

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DataBinding Expressions in Asp.Net

A DataBinding expression is a special type of expression not evaluated until runtime. You mark a databinding expression in a page by wrapping the expression in opening <%# and closing %> brackets.

A DataBinding expression isn’t evaluated until a control’s DataBinding event is raised.

When you bind a DataBound control to a DataSource control declaratively, this event is raised automatically. When you bind a DataSource control to a data source programmatically, the DataBinding event is raised when you call the DataBind() method.

Example:

Suppose you have a movies table in your database. It has two columns named "Title" and "DateReleased".

<asp:DataList id="DataList1" DataSourceId="srcMovies" Runat="server">
    <ItemTemplate>
    <b>Movie Title:</b> <%#Eval("Title")%>
    <br />
    <b>Date Released:</b> <%#Eval("DateReleased", "{0:D}") %>
    <hr />
    </ItemTemplate>
    </asp:DataList>

<asp:SqlDataSource
id="srcMovies"
ConnectionString="your connection string"
SelectCommand="SELECT Title,DateReleased FROM Movies"
Runat="server" />

The first DataBinding expression displays the title of the movie and the second DataBinding expression displays the date the movie was released. Both DataBinding expressions call the Eval() method. The Eval() method is a protected method of the Page class. Behind the scenes, the Page.Eval() method calls the static
(shared) DataBinder.Eval() method. If you want to be verbose, instead of using the Eval() method, you could use the following two expressions:

<%# DataBinder.Eval(Container.DataItem, “Title”) %>
<%# DataBinder.Eval(Container.DataItem, “DateReleased”, “{0:D}” ) %>

In ASP.NET version 1.x, you had to use DataBinder.Eval() when displaying data items in a template.
You can use <%# FormatTitle(Eval(“Title”)) %>. This method formats each of the titles displayed by the Repeater control by making each title bold and uppercase

Note: Technically, the Eval() method uses reflection when evaluating the data item to find
a property with a certain name. You do pay a performance penalty when you use
reflection.

As an alternative, you can improve the performance of your DataBinding expressions by casting the data items to a particular type like this:

<%# ((System.Data.DataRowView)Container.DataItem)[“Title”] %>

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