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COMP 1020 (6)

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University of Manitoba
Computer Science
COMP 1020
Pourang Irani

problem. SelectedIndex returns a zero-based index number that represents where the row occurs in the grid. This isn’t the information you need to insert into the query that gets the related records. Instead, you need a unique key field from the corresponding row. For example, if you have a table of products, you need to be able to get the ProductID for the selected row. In order to get this information, you need to tell the GridView to keep track of the key field values. The way you do this is by setting the DataKeyNames property for the GridView. This property requires a comma-separated list of one or more key fields. Each name you supply must match one of the fields in the bound data source. Usually, you’ll have only one key field. Here’s an example that tells the GridView to keep track of the CategoryID values in a list of product categories: Once you’ve established this link, the GridView is nice enough to keep track of the key fields for the selected record. It allows you to retrieve this information at any time through the SelectedDataKey property. Often, a database search will return too many rows to be realistically displayed in a single page. If the client is using a slow connection, an extremely large GridView can take a frustrating amount of time to arrive. Once the data is retrieved, the user may find out it doesn’t contain the right content anyway or that the search was too broad and they can’t easily wade through all the results to find the important information. The GridView handles this scenario with an automatic paging feature. When you use automatic paging, the full results are retrieved from the data source and placed into a DataSet. Once the DataSet is bound to the GridView, however, the data is subdivided into smaller groupings (for example, with 20 rows each), and only a single batch is sent to the user. The other groups are abandoned when the page finishes processing. When the user moves to the next page, the same process is repeated—in other words, the full query is performed once again. The GridView extracts just one group of rows, and the page is rendered. To allow the user to skip from one page to another, the GridView displays a group of pager controls at the bottom of the grid. These pager controls could be previous/next links (often displayed as < and >) or number links (1, 2, 3, 4, 5, . . . ) that lead to specific pages. If you’ve ever used a search engine, you’ve seen paging at wo
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