ASP.NET 4 Unleased - p 170 docx
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CHAPTER 37 Building Templated Databound Controls
LISTING 37.8 ShowProductForm.aspx
<%@ Page Language=”C#” %>
<%@ Register TagPrefix=”custom” Namespace=”myControls” %>
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”
“ /><script runat=”server”>
void Page_Load()
{
if (!Page.IsPostBack)
{
ProductForm1.Name = “Laptop”;
ProductForm1.Price = 433.12m;
ProductForm1.DataBind();
}
}
protected void ProductForm1_ProductUpdated(object sender, EventArgs e)
{
lblName.Text = ProductForm1.Results[“Name”].ToString();
lblPrice.Text = ProductForm1.Results[“Price”].ToString();
}
</script>
<html xmlns=” >
<head id=”Head1” runat=”server”>
<title>Show ProductForm</title>
</head>
<body>
<form id=”form1” runat=”server”>
<div>
<custom:ProductForm
id=”ProductForm1”
Runat=”server” OnProductUpdated=”ProductForm1_ProductUpdated”>
<EditItemTemplate>
<asp:Label
id=”lblName”
Text=”Product Name:”
AssociatedControlID=”txtName”
Runat=”server” />
<asp:TextBox
id=”txtName”
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Creating Templated Controls
Text=’<%# Bind(“Name”) %>’
Runat=”server” />
<br /><br />
<asp:Label
id=”lblPrice”
Text=”Product Price:”
AssociatedControlID=”txtPrice”
Runat=”server” />
<asp:TextBox
id=”txtPrice”
Text=’<%# Bind(“Price”) %>’
Runat=”server” />
<br /><br />
<asp:Button
id=”btnUpdate”
Text=”Update”
Runat=”server” />
</EditItemTemplate>
</custom:ProductForm>
<hr />
New Product Name:
<asp:Label
id=”lblName”
Runat=”server” />
<br /><br />
New Product Price:
<asp:Label
id=”lblPrice”
Runat=”server” />
</div>
</form>
</body>
</html>
In the Page_Load() method in Listing 37.8, the ProductForm Name and Price properties
are set. Next, the DataBind() is called to cause the ProductForm control to evaluate its
databinding expressions.
The ProductForm control’s EditItemTemplate includes Bind() expressions instead of
Eval() expressions. You use Bind() expressions in a two-way databinding template.
37
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CHAPTER 37 Building Templated Databound Controls
The EditItemTemplate includes a Button control. When you click the Button control, the
ProductForm control’s OnBubbleEvent() method executes, the values are retrieved from the
EditItemTemplate, and the ProductUpdated event is raised.
The page in Listing 37.8 handles the ProductUpdated event and displays the new values
with two Label controls (see Figure 37.3).
FIGURE 37.3 Using a two-way databinding template.
Creating Templated Databound Controls
In this section, you learn how to build templated databound controls. A databound
control can be bound to a DataSource control such as the SqlDataSource or
ObjectDataSource controls.
The ASP.NET Framework provides you with a number of base classes that you can use
when creating a custom databound control. So, let’s look at some tables and figures.
Table 37.1 lists the base control classes for all the standard ASP.NET databound controls.
Figure 37.4 displays the inheritance hierarchy of all the new databound controls in
ASP.NET Framework. Typically, you inherit from one of the leaf nodes. You create a
control that derives from the base CompositeDataBoundControl,
HierarchicalDataBoundControl, or ListControl class.
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Creating Templated Controls
This chapter concentrates on inheriting new controls from the base
CompositeDataBoundControl class. This is the easiest base class to use when you want to
display one or more database records and use templates.
NOTE
You learne d how to create c ont rol s that inherit from the base ListControl class in
Chapter 10, “Using List Controls.”
Creating a DivView Control
Let’s start simple. In this section, we create a custom databound control named the
DivView control, which displays a set of data items (database records) in HTML <div> tags.
The DivView control inherits from the base CompositeDataBoundControl class and over-
rides a single method of the base class. The DivView control overrides the base class’s
CreateChildControls() method.
The DivView control is contained in Listing 37.9.
37
FIGURE 37.4 Databound control inheritance hierarchy.
TABLE 37.1 Base Databound Control Classes
Control Base Control
ListView DataBoundControl
GridView, DetailsView, FormView
CompositeDataBoundControl
Menu, TreeView
HierarchicalDataBoundControl
DropDownList, ListBox RadioButtonList, CheckBoxList,
BulletedList
ListControl
DataList, DataGrid BaseDataList
Repeater Control
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CHAPTER 37 Building Templated Databound Controls
LISTING 37.9 DivView.cs
using System;
using System.Collections;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace AspNetUnleashed
{
public class DivView : CompositeDataBoundControl
{
private ITemplate _itemTemplate;
[TemplateContainer(typeof(DivViewItem))]
[PersistenceMode(PersistenceMode.InnerProperty)]
public ITemplate ItemTemplate
{
get { return _itemTemplate; }
set { _itemTemplate = value; }
}
protected override int CreateChildControls(IEnumerable dataSource, bool
dataBinding)
{
int counter = 0;
foreach (object dataItem in dataSource)
{
DivViewItem contentItem = new DivViewItem(dataItem, counter);
_itemTemplate.InstantiateIn(contentItem);
Controls.Add(contentItem);
counter++;
}
DataBind(false);
return counter;
}
protected override HtmlTextWriterTag TagKey
{
get
{
return HtmlTextWriterTag.Div;
}
}
}
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Creating Templated Databound Controls
37
public class DivViewItem : WebControl, IDataItemContainer
{
private object _dataItem;
private int _index;
public object DataItem
{
get { return _dataItem; }
}
public int DataItemIndex
{
get { return _index; }
}
public int DisplayIndex
{
get { return _index; }
}
protected override HtmlTextWriterTag TagKey
{
get
{
return HtmlTextWriterTag.Div;
}
}
public DivViewItem(object dataItem, int index)
{
_dataItem = dataItem;
_index = index;
}
}
}
The DivView control supports an ItemTemplate used to format each of its data items. You
are required to supply an ItemTemplate when you use the DivView control.
All the work happens in the CreateChildControls() method. This is not the same
CreateChildControls() method included in the base System.Web.UI.Control class. The
DivView control overrides the CompositeDataBounControl’s CreateChildControls()
method.
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The CreateChildControls() method accepts the following two parameters:
. dataSource—Represents all the data items from the data source.
. dataBinding—Represents whether the CreateChildControls() method is called
when the data items are retrieved from the data source.
The CreateChildControls() method is called every time that the DivView control renders
its data items. When the control is first bound to a DataSource control, the dataSource
parameter represents the data items retrieved from the DataSource control. After a post-
back, the dataSource parameter contains a collection of null values, but the correct
number of null values.
After a postback, the contents of the data items can be retrieved from View State. As long
as the correct number of child controls is created, the Framework can rebuild the contents
of the databound control.
You can use the dataBinding parameter to determine whether the data items from the
data source actually represent anything. Typically, the dataBinding parameter has the
value True when the page first loads and the value False after each postback.
The DataBind() method is called after the child controls are created. You must call the
DataBind() method when a template includes databinding expressions. Otherwise, the
databinding expressions are never evaluated.
The page in Listing 37.10 illustrates how you can bind the DivView control to a
SqlDataSource control.
LISTING 37.10 ShowDivView.aspx
<%@ Page Language=”C#” %>
<%@ Register TagPrefix=”custom” Namespace=”AspNetUnleashed” %>
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”
“
<html xmlns=” >
<head id=”Head1” runat=”server”>
<style type=”text/css”>
.movies
{
width:500px;
}
.movies div
{
border:solid 1px black;
padding:10px;
margin:10px;
CHAPTER 37 Building Templated Databound Controls
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Creating Templated Databound Controls
37
}
</style>
<title>Show DivView</title>
</head>
<body>
<form id=”form1” runat=”server”>
<div>
<custom:DivView
id=”lstMovies”
DataSourceID=”srcMovies”
CssClass=”movies”
Runat=”Server”>
<ItemTemplate>
<h1><%# Eval(“Title”) %></h1>
Director: <%# Eval(“Director”) %>
</ItemTemplate>
</custom:DivView>
<asp:SqlDataSource
id=”srcMovies”
ConnectionString=”<%$ ConnectionStrings:Movies %>”
SelectCommand=”SELECT Title, Director FROM Movies”
Runat=”server” />
<br />
<asp:LinkButton
id=”lnkReload”
Text=”Reload”
Runat=”server” />
</div>
</form>
</body>
</html>
In Listing 37.10, the SqlDataSource control represents the Movies database table. The
DivView control includes an ItemTemplate that formats each of the columns from this
database table (see Figure 37.5).
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CHAPTER 37 Building Templated Databound Controls
Summary
This chapter was devoted to the topic of building templated databound controls. In the
first part, you learned how to support templates in your custom controls. You learned how
to create templates that support both one-way and two-way databinding expressions. You
also learned how to create a default template for a control.
The second half of this chapter focused on the topic of building databound controls. You
learned how to create a simple DivView control that displays the records from a database
table in a series of HTML <div> tags.
FIGURE 37.5 Displaying database records with the DivView control.
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CHAPTER 38
Using Server-Side
ASP.NET AJAX
IN THIS CHAPTER
. The Ajax Vision
. Server-Side Ajax versus Client-
Side Ajax
. Debugging Ajax Applications
. Using the UpdatePanel Control
. Using the Timer Control
. Using the UpdateProgress
Control
. Summary
Users of modern web applications have changed quite a
bit since the first days of the web. When the web was new
and when functional, commercial websites were few and far
between, the users of web applications were a generally
complacent and easy-to-please audience.
Today, web application users don’t just want more, they
demand more. They demand that websites be fast, respon-
sive, and interactive. They don’t want an entire page to
reload just because a small piece needs to be changed. Most
important, they don’t want to sit and wait in front of an
unresponsive user interface while background processing
takes place.
To meet the increasing demands of web users, a new tech-
nology called AJAX (Asynchronous JavaScript and XML)
was created. This enabled already-rendered web pages to
make asynchronous calls and retrieve XML, which could
then be used to modify the existing page. The first evidence
of this type of technology actually showed up in Microsoft
Outlook’s web access product. Since then, web application
users have been demanding unprecedented levels of interac-
tivity and responsiveness.
The key to giving users this responsiveness lies in the
combination of asynchronous messaging calls and
JavaScript (or jQuery or any number of JavaScript-based
frameworks). In this chapter you learn about one small
piece of this puzzle: Microsoft’s server-side Ajax controls
such as the UpdatePanel, a control that enables postbacks
within a region of the page to modify only that portion of
the page and not interrupt the user’s overall experience. We
also provide an overview of two controls that support the
UpdatePanel: the
Timer and the UpdateProgress.
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