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Selecting a row means that the user can highlight or change the appearance of a row by clicking some sort of button or link. When the user clicks the button, not only will the row change its appearance, but also your code will have the opportunity to handle the event. The GridView provides built-in support for selection. You simply need to add a CommandField column with the ShowSelect property set to true. The CommandField can be rendered as a hyperlink, a button, or a fixed image. You choose the type using the ButtonType property. You can then specify the text through the SelectText property or specify the link to the image through the SelectImageUrl property. Here s an example that displays a select button: <asp:CommandField ShowSelectButton="True" ButtonType="Button" SelectText="Select" /> And here s an example that shows a small clickable icon: <asp:CommandField ShowSelectButton="True" ButtonType="Image" SelectImageUrl="select.gif" /> Figure 10-5 shows both types of select buttons. Clicking either one selects the row. When you click a select button, the page is posted back, and a series of steps unfolds. First, the GridView.SelectedIndexChanging event fires, which you can intercept to cancel the operation. Next, the GridView.SelectedIndex property is adjusted to point to the selected row. Finally, the GridView.SelectedIndexChanged event fires, which you can handle if you want to manually update other controls to reflect the new selection. When the page is rendered, the selected row is given the SelectedRowStyle.

To get around these limitations, you should consider the ObjectDataSource. The ObjectDataSource allows you to bind your page to a custom data access component. Best of all, you get almost all the same frills, such as design-time data binding and no need to write code in your web page.

For selection to work, you must configure the SelectedRowStyle so that selected rows look different from normal rows. Usually, selected rows will have a different BackColor property.

For selection to work, you must configure the SelectedRowStyle so that selected rows look different from normal rows. Usually, selected rows will have a different BackColor property.

The ObjectDataSource allows you to create a declarative link between your web-page controls and a data access component that queries and updates data. The ObjectDataSource is remarkably flexible and can work with a variety of different components. However, to use it, your data access class must conform to a few rules: It must be stateless. That s because the ObjectDataSource will create an instance only when needed and destroy it at the end of every request. It must have a default, no-argument constructor. All the logic must be contained in a single class. (If you want to use different classes for selecting and updating your data, you ll need to wrap them in another higher-level class.) None of the linked methods (for selecting or updating records) can be static. It must provide the query results when a single method is called. The query results are several records, which can be represented as a collection, an array, or a list object that implements IEnumerable. Each record should be a custom object that exposes all its data through public properties. You can work around many of these rules by handling ObjectDataSource events and writing custom code. However, if you want your data access class to plug into the data-binding model seamlessly without extra work, you should observe these guidelines.

As demonstrated in the previous chapter, you can bind other data sources to a property in a control using parameters. For example, you could add two GridView controls and use information from the first GridView to perform a query in the second. In the case of the GridView, the property you need to bind is SelectedIndex. However, this has one problem. SelectedIndex returns a zero-based index number representing 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 key field from the corresponding row. Fortunately, the GridView makes it easy to retrieve this information using the SelectedDataKeys property. To use this feature, you must set the GridView.DataKeyNames property, with a commaseparated list of one or more key fields. Each name you supply must match one of the properties of the bound object or one of the fields of the bound record.

As demonstrated in the previous chapter, you can bind other data sources to a property in a control using parameters. For example, you could add two GridView controls and use information from the first GridView to perform a query in the second.