Digg
del.icio.us
Newsvine
Facebook
Google
LinkedIn
MySpace
Reddit
Slashdot
StumbleUpon
Technorati
Twitter
Windows Live
YahooBuzz
FriendFeedASP.NET Developer's Cookbook, Chapter 13
Chapter 13: Rendering Data with ASP.NET Web Controls
13.0. Introduction
ASP.NET provides several Web controls that make displaying data on a Web page easier than ever before. This chapter shows you how to take advantage of a process called data-binding to easily display data in a variety of formats using very little code. This chapter covers many of the most commonly used features of the Repeater, DataList, and DataGrid, including some fairly advanced DataGrid features. Using these data-bound Web controls, it is very easy to write data-driven Web Forms by just dragging and dropping a few controls onto a form and writing a few lines of code.
13.1. Rendering Data Directly on a Web Form
You want to display a piece of data on a Web Form using data-binding.
Technique
You can use the <%#%> syntax to easily bind data to a control. Simply create a variable, assign it a value, and call Page.DataBind to bind it to the page. The ASPX page is as follows:
<html>
<body>
<form id="Recipe1401vb" method="post" runat="server">
<asp:Label ID="MyLabel" Runat="server">Hello <%#FirstName%>!
</asp:Label>
</form>
</body>
</html>
In <script runat="server" /> block or codebehind:
Protected FirstName as string Sub Page_Load(sender As Object, e As EventArgs) FirstName="Jeremy" Page.DataBind() End Sub
Comments
If you are using codebehind, it is important to declare the variable with Protected access level so the page can access it. It is also important to realize that calling Page.DataBind() will result in all controls on the page being data-bound, because any time a control container calls its DataBind() method, it recursively calls the DataBind() method of all of its child controls.
See Also - Section 13.2, "Data-binding to a DropDownList"
Section 13.3, "Data-binding to a Repeater"
Section 13.4, "Data-binding to a DataList"
Section 13.7, "Data-binding to a DataGrid"
13.2. Data-binding to a DropDownList
You want to create a DropDownList that is populated from a database.
Technique
To data-bind a DropDownList to a data container such as a dataset or datareader, you must set three properties and call one method. The following example demonstrates this.
In <script runat="server" /> block or codebehind:
Sub Page_Load(sender As Object, e As EventArgs)
'object vars
Dim sqlConnection As SqlConnection
Dim sqlDataAdapter As SqlDataAdapter
Dim sqlCommand As SqlCommand
Dim dataSet As DataSet
Dim dataTable As DataTable
Try
sqlConnection = New SqlConnection("Integrated Security=yes; _
Initial Catalog=Northwind; _
Data Source=(local)")
'pass the stored proc name and SqlConnection
sqlCommand = New SqlCommand("Select * From Customers", _
sqlConnection)
'instantiate SqlAdapter and DataSet
sqlDataAdapter = New SqlDataAdapter(sqlCommand)
dataSet = New DataSet()
'populate the DataSet
sqlDataAdapter.Fill(dataSet, "Customers")
'apply sort to the DefaultView to sort by CompanyName
dataSet.Tables(0).DefaultView.Sort = "CompanyName"
DropDownList1.DataSource = _
dataSet.Tables("Customers").DefaultView
DropDownList1.DataTextField = _
"CompanyName" ' what to display
DropDownList1.DataValueField = _
"CustomerID" ' what to set as value
DropDownList1.DataBind()
Catch exception As Exception
errorMsgLabel.Text = exception.ToString()
End Try
End Sub
Comments
As a general rule, you can perform this kind of data-binding only when the form first loads, as opposed to on every postback. To do this, simply place the data access and data-binding code within an If statement so that they are only performed when Page.IsPostback is false (for example, on the first load of the page). You can manipulate the Items collection after calling DataBind() if you need to set a particular item as Selected (use Items.FindByText or Items.FindByValue to find the item you want) or insert a default entry for the first item (use Items.Insert() with an index of 0 for the first item).
See Also - ASP.NET DropDownList I—http://aspalliance.com/stevesmith/articles/ dotnetlistbox1.asp
ASP.NET DropDownList II—http://aspalliance.com/stevesmith/articles/ dotnetlistbox2.asp
Dynamically Set Text and Value of DropDownList—http://aspalliance.com/aldotnet/ examples/dynamicdatasource.aspx
13.3. Data-binding to a Repeater
You want to use a repeater to output the results of a data query.
Technique
The Repeater control is the simplest of three templated data-bound controls provided with ASP.NET (the others being the DataList and DataGrid). It supports templates for Header, Item, AlternatingItem, Separator, and Footer, which can each contain static and dynamic (data-bound) content. The following example demonstrates how to set up a Repeater's templates and how to data-bind the Repeater to a dataset.
The ASPX page is as follows:
<asp:Repeater id="Repeater1" runat="server">
<HeaderTemplate>Customers:<br/><ul></HeaderTemplate>
<ItemTemplate>
<li><%#DataBinder.Eval(Container.DataItem, "CompanyName")%>,
<%#DataBinder.Eval(Container.DataItem, "ContactName")%></li>
</ItemTemplate>
<AlternatingItemTemplate>
<li><font color="red">
<%#DataBinder.Eval(Container.DataItem, "CompanyName")%>,
<%#DataBinder.Eval(Container.DataItem, "ContactName")%></font></li>
</AlternatingItemTemplate>
<FooterTemplate><hr/>Data Retrieved at:
<%# System.DateTime.Now.ToString() %></FooterTemplate>
</asp:Repeater>
<br>
<br>
<asp:Label id="errorMsgLabel" runat="server"
Width="327px" Height="111px"></asp:Label>
In <script runat="server" /> block or codebehind:
Sub BindRepeater()
'object vars
Dim sqlConnection As SqlConnection
Dim sqlDataAdapter As SqlDataAdapter
Dim sqlCommand As SqlCommand
Dim dataSet As DataSet
Dim dataTable As DataTable
Try
sqlConnection = New SqlConnection("Integrated Security=yes; _
Initial Catalog=Northwind; _
Data Source=(local)")
'pass the stored proc name and SqlConnection
sqlCommand = New SqlCommand("Select * From Customers", _
sqlConnection)
'instantiate SqlAdapter and DataSet
sqlDataAdapter = New SqlDataAdapter(sqlCommand)
dataSet = New DataSet()
'populate the DataSet
sqlDataAdapter.Fill(dataSet, "Customers")
'apply sort to the DefaultView to sort by CompanyName
dataSet.Tables(0).DefaultView.Sort = "CompanyName"
Repeater1.DataSource = dataSet.Tables("Customers").DefaultView
Repeater1.DataBind()
Catch exception As Exception
errorMsgLabel.Text = exception.ToString()
End Try
End Sub
Comments
BindRepeater() is called by Page_Load only when it is first loaded (not after a postback). It will automatically retain its state between postbacks using ViewState, thus avoiding additional requests to the database.
See Also - Repeater Class—http://msdn.microsoft.com/library/en-us/cpref/html/ frlrfsystemwebuiwebcontrolsrepeaterclasstopic.asp
From ASP.NET Developer's Cookbook by Steven A. Smith and Rob Howard published by Sams Publishing -- © Copyright Pearson Education. All rights reserved.
Comments
There are no comments yet. Be the first to comment!