I once discussed data binding with a
junior developer who wanted to display text in a Repeater control
but didn’t have a database connection to use as its data source. I
pointed out that he could utilize data binding within the .NET
Framework.

Data binding provides enormous power and
flexibility when developing .NET applications. Learn what data
binding is and how you can bind data to various structures within
.NET.

Data binding defined

Data binding is binding controls to data, which
may originate in a relational database or another data structure.
Data binding allows you to bind a control to a specific column from
a database table or element within a data structure. Basically,
data binding provides a simple, convenient, and powerful way to
create a link between a control and application data.

I’ll concentrate on ASP.NET controls in this
article. ASP.NET provides various data controls that may utilize
data binding. These controls include (but aren’t limited to) the
following:

  • DropDownList
  • ListBox
  • DataGrid
  • DataList
  • Repeater
  • CheckBoxList
  • RadioButtonList

Binding a control to a database resultset

The following C# code is in the codebehind file
for your sample ASP.NET page. It issues a simple command to a MySQL
database server. The command (SHOW DATABASE) retrieves a list of
available databases. Note: The MySQL
Connector/Net 1.0 is used to connect to MySQL. It’s referenced
in the code by the following using statement:

using MySql.Data.MySqlClient;

Here’s the Page_Load portion of the codebehind
file:

protected System.Web.UI.WebControls.Repeater
Repeater1;
void Page_Load(object sender, System.EventArgs e) {
string connStr = “server=localhost; database=sitepoint;
pooling=false”;
MySqlConnection conn = null;
MySqlDataReader reader = null;
MySqlCommand cmd = null;
try {
conn = new MySqlConnection( connStr );
conn.Open();
cmd = new MySqlCommand(“SHOW DATABASES”, conn);
reader = cmd.ExecuteReader();
Repeater1.DataSource = reader;
Repeater1.DataBind();
} catch (MySqlException ex)  {
Response.Write(“MySQL Exception: ” + ex.Message);
}  catch (Exception ex) {
Response.Write(“Exception: ” + ex.Message);
} finally     {
if (reader != null) reader.Close();
if (conn != null) conn.Close();
} }

The corresponding ASP.NET Web Form contains a
Repeater control. Notice that this control is tied to your database
query by assigning the Repeater’s DataSource property to the result
set (MySqlDataReader object). The data bind is enforced with a call
to the Repeater’s DataBind method. All of the controls contain the
DataSource property and the DataBind method.

The corresponding ASP.NET source is below:

<%@ Page language=”c#”
Codebehind=”BuilderSample2.aspx.cs”
AutoEventWireup=”false”
Inherits=”BuilderDataBindingCSharp.BuilderSample2″ %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<html><head><title>Builder
Sample</title></head>
<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<table>
<asp:Repeater id=”Repeater1″ runat=”server”>
<ItemTemplate>
<tr>
<td><%# DataBinder.Eval(Container.DataItem, “Database”)
%></td>
</tr>
</ItemTemplate>
</asp:Repeater>
</table>
</form></body></html>

The Repeater control is contained in an HTML
table for formatting. The DataBinder.Eval statement retrieves the
specified column value from the data source tied to the control. In
this instance, the Database column is returned. Notice that the
result of the SHOW DATABASE returns values assigned to the name
Database.

Let’s take the concept further by binding
different data structures.

Binding controls to other data structures

The wonderful thing about data binding is that
you aren’t restricted to data from a database call. You can create
and populate your own custom data structures, or you can use ones
in the .NET Framework. This includes ArrayList, Hashtable, and
regular arrays.

For example, you may want to create an array of
custom object types and bind it to a control. The next example
binds an ArrayList object (from the System.Collections namespace)
containing custom object types (Person) to a Repeater control. The
Person class is included with the code for brevity, but it would
most likely exist in its own class file in a production
environment.

<%@ Page language=”c#” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”C#” runat=”server”>
public class Person {
public Person() { }
private string firstName;
private string lastName;
public string FirstName {
get {
return this.firstName;
}
set {
this.firstName = value;
} }
public string LastName {
get {
return this.lastName;
}
set {
this.lastName = value;
} } }
private void Page_Load(object sender, System.EventArgs e) {
ArrayList alTest = new ArrayList(3);
Person p1 = new Person();
p1.FirstName = “Lenny”;
p1.LastName = “Dykstra”;
alTest.Add(p1);
Person p2 = new Person();
p2.FirstName = “John”;
p2.LastName = “Kruk”;
alTest.Add(p2);
rptPeople.DataSource = alTest;
rptPeople.DataBind();
}
</script>
<html><head><title>WebForm1</title></head>

<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<asp:Repeater id=”rptPeople” runat=”server”>
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, “LastName”)
%>,
<%# DataBinder.Eval(Container.DataItem, “FirstName”)
%>
<br />
</ItemTemplate>
</asp:Repeater>
</form></body></html>

Notice that the code creates two instances of
the People class and adds them to the ArrayList object. The
property names from the Person class are used to assign column
names (DataBinder.Eval statement) to the Repeater control within
the ASP.NET source. A normal array object works in the same
manner.

The VB.NET equivalent follows (notice that
fName and lName are used in place of firstName and lastName since
VB.NET isn’t case-sensitive):

<%@ Page language=”vb” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”vb” runat=”server”>
Public Class Person
Private fName As String
Private lName As String
Public Property FirstName As String
Get
return Me.fName
End Get
Set
Me.fName = value
End Set
End Property
Public Property LastName As String
Get
return Me.lName
End Get
Set
Me.lName = value
End Set
End Property
End Class
Sub Page_Load
Dim alTest As ArrayList
Dim p1 As New Person()
alTest = New ArrayList(3)
p1.FirstName = “Lenny”
p1.LastName = “Dykstra”
alTest.Add(p1)
Dim p2 As New Person()
p2.FirstName = “John”
p2.LastName = “Kruk”
alTest.Add(p2)
rptPeople.DataSource = alTest
rptPeople.DataBind()
End Sub
</script>
<html><head><title>WebForm1</title></head>

<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<asp:Repeater id=”rptPeople” runat=”server”>
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, “LastName”)
%>,
<%# DataBinder.Eval(Container.DataItem, “FirstName”)
%>
<br />
</ItemTemplate>
</asp:Repeater>
</form></body></html>

Another option is the Hashtable object located
in the System.Collections namespace. A Hashtable represents a
collection of key-and-value pairs organized by the hash code of the
key. The Hashtable’s Add method is used to add items to it, with
the first parameter being the key and the second containing the
associated value.

When using a Hashtable for data binding, you
should use Key and Value to assign elements to a control via the
DataBinder.Eval statement. The following ASP.NET source shows this
in action using C#:

<%@ Page language=”c#” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”C#” runat=”server”>
private void Page_Load(object sender, System.EventArgs e) {
Hashtable ht = new Hashtable(3);
ht.Add(“Development”, “Builder.com”);
ht.Add(“News”, “News.com”);
ht.Add(“Technology”, “TechRepublic.com”);
rptPeople.DataSource = ht;
rptPeople.DataBind();
}
</script>
<html>
<head><title>Bind with
Hashtable</title>    </head>
<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<h1>Notable Web Sites</h1>
<table cellpadding=”5″ border=”1″>
<asp:Repeater id=”rptPeople” runat=”server”>
<ItemTemplate>
<tr><td><%# DataBinder.Eval(Container.DataItem,
“Key”) %></td>
<td><%# DataBinder.Eval(Container.DataItem, “Value”)
%></td>
</tr>
</ItemTemplate>
</asp:Repeater>
</table></form></body></html>

The equivalent VB.NET code follows:

<%@ Page language=”vb” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”vb” runat=”server”>
Sub Page_Load
Dim ht As Hashtable
ht = New Hashtable
ht.Add(“Development”, “Builder.com”)
ht.Add(“News”, “News.com”)
ht.Add(“Technology”, “TechRepublic.com”)
rptPeople.DataSource = ht
rptPeople.DataBind()        

End Sub
</script>
<html>
<head><title>Bind with
Hashtable</title>    </head>
<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<h1>Notable Web Sites</h1>
<table cellpadding=”5″ border=”1″>
<asp:Repeater id=”rptPeople” runat=”server”>
<ItemTemplate>
<tr><td><%# DataBinder.Eval(Container.DataItem,
“Key”) %></td>
<td><%# DataBinder.Eval(Container.DataItem, “Value”)
%></td>
</tr></ItemTemplate></asp:Repeater>
</table></form></body></html>

Though I’ve focused on the Repeater control, a
Hashtable would work as well as any other control. The following
sample demonstrates this with the Hashtable’s key used as the value
behind the ListBox control:

<%@ Page language=”c#” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”C#” runat=”server”>
private void Page_Load(object sender, System.EventArgs e) {
Hashtable ht = new Hashtable(3);
ht.Add(“Development”, “Builder.com”);
ht.Add(“News”, “News.com”);
ht.Add(“Technology”, “TechRepublic.com”);
lstStatus.DataSource = ht;
lstStatus.DataTextField = “Value”;
lstStatus.DataValueField = “Key”;
lstStatus.DataBind();
}
</script>
<html><head><title>ListBox HashTable
Example</title></head>
<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<asp:ListBox id=”lstStatus” runat=”server” />
</form></body></html>

The VB.NET equivalent follows:

<%@ Page language=”vb” %>
<%@ Import Namespace=”System.Collections” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”
>
<script language=”VB” runat=”server”>
Sub Page_Load
Dim ht As Hashtable
ht = New Hashtable(3)
ht.Add(“Development”, “Builder.com”)
ht.Add(“News”, “News.com”)
ht.Add(“Technology”, “TechRepublic.com”)
lstStatus.DataSource = ht
lstStatus.DataTextField = “Value”
lstStatus.DataValueField = “Key”
lstStatus.DataBind()
End Sub
</script>
<html><head><title>ListBox HashTable
Example</title></head>
<body>
<form id=”frmBuilderSample” method=”post”
runat=”server”>
<asp:ListBox id=”lstStatus” runat=”server” />
</form>    </body></html>

These examples demonstrate the use of arrays
and a Hashtable object to bind data to a control. After witnessing
the benefits of data binding, I hope you’ll add it to your
development toolbox.

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