Retrieving Data with AJAX and the GridView Control
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In this second part of a four-part series focusing on ASP.NET applications featuring AJAX, you'll learn how to use the GridView control. This article is excerpted from chapter four of
Learning ASP.NET 2.0 with AJAX: A Practical Hands-on Guide, written by Jesse Liberty, Dan Hurwitz and Brian MacDonald (O'Reilly, 2007; ISBN: 0596513976). Copyright © 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.
Using the GridView Control
Now that the DataSource control is providing the data you want, you need a way to display it. From the Data section of the Toolbox, drag a GridView control onto the page. The GridView control recognizes that a SqlDataSource is on the page and does not create its own.
If you had dragged the GridView onto the page first, it would have given you the opportunity to create a SqlDataSource rather than assuming you’d like to use one already in existence. It pretty much amounts to the same thing.
Click on the GridView’s Smart Tag (if it is not already open). Click the drop-down menu next to “Choose Data Source” and select the DataSource control you just created, as shown in Figure 4-12.
Figure 4-12. The Smart Tag of the GridView control lets you select the data source you want to use.
Once the data source is set, the data grid is redrawn, with a column for each field returned by the data source. The column headers are filled in for you based on the column names in the table that the data source represents.
You’ll have an opportunity to make the grid look much prettier, in just a short while.
Open the Smart Tag again and check “Enable Paging,” which allows the grid to show a limited number of entries on each page and provide links to the other pages providing access to all the data. Also check “Enable Sorting,” which allows the user to sort the grid by clicking on a column header.
Set the page to be the start page for the application (right-click the page in the Solution Explorer and select “Set As Start Page”) and then run the application. Figure 4-13 demonstrates how the screen should appear.
Notice that the MakeFlag column (which is a Boolean value of some obscure use to the AdventureWorks business model) is shown as a checkbox. Also note that each of the column headers are shown as links. Click on one of them now—you see that the grid is sorted by that column. Also notice that at the bottom of the grid are links to page through more data, 10 rows at a time. Click on some of those too, to see the various pages.
Figure 4-13. With the GridView in place and connected to the data source, you can see the data
you asked for. Notice the clickable headings and the paging links.
Each time you click on one of the columns or one of the page numbers the entire page is posted back to the server, and you’ll encounter a noticeable delay and flicker. You know how to fix that!
Close the browser and return to Design view. Drag an UpdatePanel control onto the page from the AJAX Extensions section of the Toolbox. Drag both the SqlDataSource and GridView controls already on the page into the UpdatePanel.
Run the application again. Notice there are no visible postbacks when you page or sort, and consequently, no flicker.
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 This article is excerpted from chapter four of Learning ASP.NET 2.0 with AJAX: A Practical Hands-on Guide, written by Jesse Liberty, Dan Hurwitz and Brian MacDonald (O'Reilly, 2007; ISBN: 0596513976). Check it out today at your favorite bookstore. Buy this book now.
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