Recipe 7.2 Binding Complex Data to Web Forms Controls

Problem

You want to bind multiple columns in multiple records to an ASP.NET control.

Solution

Set the control's advanced properties (see Table 7-1) before calling DataBind( ).

The Web Forms page sample code defines the ListBox that is populated with data by the code-behind page logic. The code for the Web Forms page is shown in Example 7-3.

Example 7-3. File: ADOCookbookCS0702.aspx

<asp:ListBox id="categoriesListBox" style="Z-INDEX: 102; LEFT: 88px;
    POSITION: absolute; TOP: 64px" runat="server" Width="184px"
    Height="216px">
</asp:ListBox>

The code-behind contains one event handler:

Page.Load

Fills a DataTable with the CategoryID and CategoryName from the Categories table in the Northwind sample database. The ListBox server control is bound to the DataTable.

The C# code for the code-behind is shown in Example 7-4.

Example 7-4. File: ADOCookbookCS0702.aspx.cs

// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient; 

//  . . . 

private void Page_Load(object sender, System.EventArgs e)
{
    // Create a DataAdapter and use it to retrieve ID and Name
    // for all categories.
    String sqlText = "SELECT CategoryID, CategoryName FROM Categories " +
        "ORDER BY CategoryName";
    SqlDataAdapter da = new SqlDataAdapter(sqlText,
        ConfigurationSettings.AppSettings["DataConnectString"]);
    DataTable table = new DataTable("Categories");
    da.Fill(table);

    // Bind the table to the list box control.
    categoriesListBox.DataSource = table.DefaultView;
    categoriesListBox.DataValueField = "CategoryID";
    categoriesListBox.DataTextField = "CategoryName";

    categoriesListBox.DataBind( );
}

Discussion

Complex data binding describes binding a multi-record control to multiple records in a data source. The DataGrid, DataList, and ListBox controls are examples of controls that support complex data binding.

Each control that supports complex data binding exposes a set of properties, which are slightly different for each control, that control the binding. These properties are described in Table 7-1.

Table 7-1. Complex data-binding properties

Property	Description
DataSource	Gets or sets the data source that the control is displaying data for. Valid data sources include DataTable, DataView, DataSet, DataViewManager, or any object that implements the IEnumerable interface.
DataMember	Gets or sets the table in the data source to bind to the control. You can use this property if the data source contains more than one table—a DataSet, for example.
DataKeyField	Gets or sets the key field in the data source. This allows the key field for a listing control to be stored and later accessed without displaying it in the control.
DataValueField	Gets or sets the field in the data source that provides the value for the control when an item is selected.
DataTextField	Gets or sets the field in the data source that provides the display value for the control when an item is selected.

After the properties appropriate to the control are set, call the DataBind( ) method of the control or of the Page to bind the data source to the server control.