Exploring Specialized Server Controls in Visual Studio .NET

Creator QR Code 2d barcode in Visual Studio .NET Exploring Specialized Server Controls

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ASP.NET data-binding syntax to insert data from the data source. Controls that sup port templates include GridView, DetailsView, and FormView. A typical control may allow the following templates to be programmed:

This is an optional header, which is rendered at the top of the This is an optional footer, which is rendered at the bottom of

This is an optional alternating item template; if imple mented, every other row is rendered using this template.

This is an optional selected item template; if imple mented, the template is used to render a row that has been selected.

This is an optional separator template that defines the sepa ration of each item and alternate item.

This is an optional edit item template that is used to render a row that is in edit mode. This usually involves displaying the data in a TextBox instead of a Label control.

The DataBinder class provides a static method called Eval, which can simplify access to data, especially when you are using templated controls. The Eval method uses reflection to perform a lookup of the DataItem property s underlying type by looking at the type metadata that is stored in the type s assembly. After the metadata is retrieved, the Eval method determines how to connect to the given field. The end result is that Eval provides a consistent method of binding to the data. The following code shows the binding to the Vin property of the Car object:

The Eval method provides an overloaded method that allows a format string to be assigned. The Price can be modified to provide currency formatting, as shown in the following code:

The problem with the Eval method is that it provides one-way, or read-only binding, but the new Bind method fixes that problem.

The Bind method provides two-way data binding, which makes this method desirable for use when editing or inserting records. Just like the Eval method, the Bind method has two overloads, which means that you can use it with or without the "format" parameter. The following code shows the use of the Bind method to the Vin property of the Car object:

The Bind method provides an overloaded method that allows a format string to be assigned. The Price can be modified to provide currency formatting, as shown in the following code:

Notice that the syntax for the Bind method is the same as for the Eval method. Also, the GridView, DetailsView, and FormView controls are the only controls that allow use of the Bind method.

A control that is data-bound using the Bind syntax must have the ID property set to a user-defined value.

The ListControl is an abstract base class that provides common functionality for its inherited classes, as shown in Figure 3-27. The ListControl contains an Items collec tion, which is a collection of ListItem objects. The ListItem contains a Text property that is displayed to the user and a Value property that is posted back to the Web server. The ListItem objects can be populated by adding new ListItems objects in code or by setting the DataSource and DataMember properties. If you set the DataSource and DataMember properties, you can choose the fields in your tabular result that you will bind to the ListItem.Text and ListItem.Value properties by setting the DataTextField and DataValueField properties, respectively. The text displayed for each item in the list control can be formatted by setting the DataTextFormatString property.

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ListControl Abstract Class DataBoundControl Properties AppendDataBoundItems AutoPostBack CausesValidation DataTextField DataTextFormatString DataValueField Items SelectedIndex SelectedItem SelectedValue TagKey Text ValidationGroup Methods ClearSelection ListControl Events SelectedIndexChanged TextChanged

The SelectedIndex property lets you get or set the index of the selected item in the ListControl. Using the SelectedItem property, you can access the selected ListItem object s properties. If you only need to access the value of the selected ListItem, use the SelectedValue property. The ListControl also provides the SelectedIndexChanged event, which is raised when the selection in the list control changes between posts to the server.