Recipe 1.3 Enhancing the Output of a Tabular Display

     

1.3.1 Problem

You need to display data from a database in a way that lets you organize and enhance the output beyond the confines of the DataGrid control's default tabular display. Selecting and editing the data are not important, nor is navigating through the data.

1.3.2 Solution

Use a Repeater control with templates and then bind the data to the control.

In the .aspx file, add a Repeater control and the associated templates for displaying the data.

In the code-behind class for the page, use the .NET language of your choice to:

  1. Open a connection to the database.

  2. Build a query string, and read the desired data from the database using an OleDbCommand and OleDbDataReader .

  3. Assign the data source to the Repeater control and bind it.

Figure 1-2 shows the appearance of a typical Repeater in a browser. Example 1-4 through Example 1-6 show the .aspx and code-behind files for an application that produces this result.

Figure 1-2. Using templates with Repeater control display output
figs/ancb_0102.gif

1.3.3 Discussion

When your primary aim is to organize and enhance the output beyond the confines of the DataGrid control's default tabular display, the Repeater control is a good choice because, unlike a DataGrid , it has associated templates that allow you to use virtually any HTML to format the displayed data. It also has the advantage of being relatively lightweight and easy to use. When using Repeater , however, there are a handful of nuances you should know about that can make life easier and, in one instance, enhance performance.

Example 1-4 shows one of the most common approaches to using the Repeater control, which is to place the asp:Repeater element in a table and use its HeaderTemplate , ItemTemplate , and AlternatingItemTemplate attributes to format the displayed data as rows in the table.

A HeaderTemplate is used to define the header row of the table. In this example, the header is straight HTML with a single table row and three columns .

An ItemTemplate formats the even-numbered rows of data, while an AlternatingItemTemplate formats the odd-numbered rows. For both templates, a single row in the table is defined with the same three columns defined in the header template. In each of the three columns, data-binding statements (described later) define the data to be placed in each of the columns. The only differences between ItemTemplate and AlternatingItemTemplate are the color schemes and stylesheet classes used to output the rows. If you do not need to output the data using alternating styles, then omit the AlternatingItemTemplate attribute.

The data from the database is bound to the cells in the templates using the DataBinder.Eval method. The Title field is placed in the first column, the ISBN field is placed in the second column, and the Publisher field is placed in the third column:

 DataBinder.Eval(Container.DataItem, "Title") DataBinder.Eval(Container.DataItem, "ISBN") DataBinder.Eval(Container.DataItem, "Publisher") 

If the header is pure HTML with no data binding required, it is more efficient to remove the HeaderTemplate attribute and place the header HTML before the asp:Repeater tag. By moving the header outside of the asp:Repeater tag, the creation of several server-side controls is eliminated, which reduces the time required to render the page and improves performance.

 <table width="100%" border="2" bordercolor="#000080"           bgcolor="#FFFFE0"           style="border-style:solid;           border-collapse:collapse;">  <thead bgcolor="#000080" class="TableHeader">   <tr>   <th align="center">Title</th>   <th align="center">ISBN</th>   <th align="center">Publisher</th>   </tr>   </thead>  <asp:Repeater id=repBooks runat="server">          ...       </asp:Repeater>     </table> 


The Page_Load method in the code-behind, shown in Example 1-5 (VB) and Example 1-6 (C#), opens a connection to the database, reads the data from the database using an OleDbCommand and an OleDbDataReader object, binds the data reader to the Repeater control, and then performs the necessary cleanup.

1.3.4 See Also

Recipe 1.6 for another example of using a template with a tabular control

More About the DataBinder.Eval Method

Recipe 1.3 uses the DataBinder.Eval method to bind data from the database to cells in the templates, as in:

 <%# DataBinder.Eval(Container.DataItem, "Title") %> 

The advantage of this approach is its relatively simple syntax. However, because the DataBinder.Eval method uses late-bound reflection to parse and evaluate a data-binding expression (in this case it's a simple string), there's a performance penalty associated with it.

If performance is your prime concern, you could use the following syntax instead:

 <%# ((DbDataRecord)Container.DataItem)["Title"] %> 

In order for this syntax to work, explicit casting is required. Also, when casting to DbDataRecord , make sure to add the following page-level directive to the beginning of your .aspx file:

 <%@ Import namespace="System.Data.Common" %> 


Example 1-4. Templates with Repeater control (.aspx)
 <%@ Page Language="vb" AutoEventWireup="false"           Codebehind="CH01TemplatesWithRepeaterVB.aspx.vb"           Inherits="ASPNetCookbook.VBExamples.CH01TemplatesWithRepeaterVB" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html>   <head>     <title>Templates with Repeater</title>     <link rel="stylesheet" href="css/ASPNetCookbook.css">   </head>   <body leftmargin="0" marginheight="0" marginwidth="0" topmargin="0">     <form id="frmData" method="post" runat="server">       <table width="100%" cellpadding="0" cellspacing="0" border="0">         <tr>           <td align="center">             <img src="images/ASPNETCookbookHeading_blue.gif">           </td>         </tr>         <tr>           <td class="dividerLine">             <img src="images/spacer.gif" height="6" border="0"></td>         </tr>       </table>       <table width="90%" align="center" border="0">         <tr>           <td><img src="images/spacer.gif" height="10" border="0"></td>         </tr>         <tr>           <td align="center" class="PageHeading">               Templates With Repeater (VB)</td>         </tr>         <tr>           <td><img src="images/spacer.gif" height="10" border="0"></td>         </tr>         <tr>           <td align="center">               <!-- Create a table within the cell to provide localized                     customization for the book list -->             <table width="100%" border="2" bordercolor="#000080"                     bgcolor="#FFFFE0"                     style="border-style:solid;border-collapse:collapse;">  <asp:Repeater id=repBooks runat="server">   <HeaderTemplate>   <thead bgcolor="#000080" class="TableHeader">   <tr>   <th align="center">Title</th>   <th align="center">ISBN</th>   <th align="center">Publisher</th>   </tr>   </thead>   </HeaderTemplate>   <ItemTemplate>   <tr bordercolor="#000080" class="TableCellNormal">   <td><%# DataBinder.Eval(Container.DataItem, "Title") %>   </td>   <td align="center">   <%# DataBinder.Eval(Container.DataItem, "ISBN") %>   </td>   <td align="center">   <%# DataBinder.Eval(Container.DataItem, "Publisher") %>   </td>   </tr>   </ItemTemplate>   <AlternatingItemTemplate>   <tr bordercolor="#000080" bgcolor="#FFFFFF"   class="TableCellAlternating">   <td><%# DataBinder.Eval(Container.DataItem, "Title") %>   </td>   <td align="center">   <%# DataBinder.Eval(Container.DataItem, "ISBN") %>   </td>   <td align="center">   <%# DataBinder.Eval(Container.DataItem, "Publisher") %>   </td>   </tr>   </AlternatingItemTemplate>   </asp:Repeater>  </table>           </td>         </tr>       </table>     </form>   </body> </html> 

Example 1-5. Templates with Repeater control code-behind (.vb)
 Option Explicit On  Option Strict On '----------------------------------------------------------------------------- ' '   Module Name: CH01TemplatesWithRepeaterVB.aspx.vb ' '   Description: This class provides the code behind for '                CH01TemplatesWithRepeaterVB.aspx ' '***************************************************************************** Imports Microsoft.VisualBasic Imports System.Configuration Imports System.Data Imports System.Data.OleDb Namespace ASPNetCookbook.VBExamples   Public Class CH01TemplatesWithRepeaterVB     Inherits System.Web.UI.Page     'controls on form     Protected repBooks As System.Web.UI.WebControls.Repeater     '*************************************************************************     '     '   ROUTINE: Page_Load     '     '   DESCRIPTION: This routine provides the event handler for the page load     '                event.  It is responsible for initializing the controls     '                on the page.     '     '-------------------------------------------------------------------------     Private Sub Page_Load(ByVal sender As System.Object, _                           ByVal e As System.EventArgs) _                 Handles MyBase.Load       Dim dbConn As OleDbConnection       Dim dCmd As OleDbCommand       Dim dReader As OleDbDataReader       Dim strConnection As String       Dim strSQL As String       If (Not Page.IsPostBack) Then         Try  'get the connection string from web.config and open a connection   'to the database   strConnection = _   ConfigurationSettings.AppSettings("dbConnectionString")   dbConn = New OleDbConnection(strConnection)   dbConn.Open( )   'build the query string and get the data from the database   strSQL = "SELECT Title, ISBN, Publisher " & _   "FROM Book " & _   "ORDER BY Title"   dCmd = New OleDbCommand(strSQL, dbConn)   dReader = dCmd.ExecuteReader( )   'set the source of the data for the repeater control and bind it   repBooks.DataSource = dReader   repBooks.DataBind( )  Finally           'cleanup           If (Not IsNothing(dReader)) Then             dReader.Close( )           End If           If (Not IsNothing(dbConn)) Then             dbConn.Close( )           End If         End Try       End If     End Sub  'Page_Load   End Class  'CH01TemplatesWithRepeaterVB End Namespace 

Example 1-6. Templates with Repeater control code-behind (.cs)
 //---------------------------------------------------------------------------- // //   Module Name: CH01TemplatesWithRepeaterCS.aspx.cs // //   Description: This class provides the code behind for //                CH01TemplatesWithRepeaterCS.aspx // //**************************************************************************** using System; using System.Configuration; using System.Data; using System.Data.OleDb; namespace ASPNetCookbook.CSExamples {   public class CH01TemplatesWithRepeaterCS : System.Web.UI.Page   {     // controls on form     protected System.Web.UI.WebControls.Repeater repBooks;          //************************************************************************     //     //   ROUTINE: Page_Load     //     //   DESCRIPTION: This routine provides the event handler for the page     //                load event.  It is responsible for initializing the     //                controls on the page.     //     //------------------------------------------------------------------------     private void Page_Load(object sender, System.EventArgs e)     {       OleDbConnection dbConn = null;       OleDbCommand dCmd = null;       OleDbDataReader dReader = null;       String strConnection = null;       String strSQL = null;       if (!Page.IsPostBack)       {         try         {  // get the connection string from web.config and open a connection   // to the database   strConnection =   ConfigurationSettings.AppSettings["dbConnectionString"];   dbConn = new OleDbConnection(strConnection);   dbConn.Open( );   // build the query string and get the data from the database   strSQL = "SELECT Title, ISBN, Publisher " +   "FROM Book " +   "ORDER BY Title";   dCmd = new OleDbCommand(strSQL, dbConn);   dReader = dCmd.ExecuteReader( );   // set the source of the data for the repeater control and bind it   repBooks.DataSource = dReader;   repBooks.DataBind( );  }         finally         {           // cleanup           if (dReader != null)           {             dReader.Close( );           }           if (dbConn != null)           {             dbConn.Close( );           }         }  // finally       }     }  // Page_Load   }  // CH01TemplatesWithRepeaterCS } 



ASP. NET Cookbook
ASP.Net 2.0 Cookbook (Cookbooks (OReilly))
ISBN: 0596100647
EAN: 2147483647
Year: 2006
Pages: 179

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