ASP.NET Web Server Controls

Basic Web Server Controls

Overview• The ASP.NET page framework includes a number of

built-in server controls that are designed to provide a more structured programming model for the Web. These controls provide the following features:– Automatic state management.– Simple access to object values without having to use the

Request object.– Ability to react to events in server-side code to create

applications that are better structured.– Common approach to building user interfaces for Web pages.– Output is automatically customized based on the capabilities

of the browser.

ASP.NET Web Server Controls• Server controls are added to a page, and

programmers write code to handle events raised by users’ interaction with the controls at runtime.

• Built in Server controls are divided into two groups:– HTML controls

• Reside in the System.Web.UI.HTMLControls namespace• Map 1-to-1 with the standard HTML elements

– Web controls• Reside in the System.Web.UI.WebControls namespace• Very similar to the Visual Basic UI controls• All Web controls use the prefix asp

Web Server Control Categories• Basic Web Controls

– Commonly used user input controls such as labels, text boxes, and drop-down lists

• Validation Controls– used to validate the values that are entered into other controls of the

page– perform client-side validation, server-side validation, or both

• List Controls– support binding to collections– display rows of data in a customized, templated format

• Rich Controls– task-specific controls with rich functionality– Examples: AdRotator and Calendar controls

Basic Web Server Controls

• Label• TextBox• CheckBox• RadioButton• DropDownList• Image• Panel• Button

• HyperLink• ImageButton• LinkButton• Literal• PlaceHolder• Table• TableCell• TableRow

Using Web Server Controls

• Add server control to page• Set server control properties• Add event handler if needed

Web Server Control Properties

• The System.Web.UI.WebControls.WebControl base class contains all of the common properties. Most of the Web server controls derive from this class.

• See the next slide for a list of common properties.

Property

AccessKey The control's keyboard shortcut key (AccessKey). It specifies a single letter or number that the user can press while pressing ALT.

Attributes The collection of additional attributes on the control not defined by a public property, but that should also be rendered. Any attribute that is not defined by the Web server control is added to this collection.

BackColor The background color of the control. The BackColor property can be set using standard HTML color identifiers: the name of a color ("black" or "red") or an RGB value expressed in hexadecimal format ("#ffffff").

BorderColor The border color of the control. The BorderColor property can be set using standard HTML color identifiers: the name of a color ("black" or "red") or an RGB value expressed in hexadecimal format ("#ffffff").

BorderWidth The width of the control's border (if any) in pixels. Note This property might not work for all controls in browsers earlier than Internet Explorer 4.0.

BorderStyle The control's border style, if any. The possible values are: NotSet, None, Dotted, Dashed, Solid, Double, Groove, Ridge, Inset, Outset

CssClass The cascading style sheets (CSS) class to assign to the control.

Style A collection of text attributes that are rendered as a CSS style attribute on the outer tag of the control. Note Any style values set using style properties (for example, BackColor) will automatically override a corresponding value in this collection.

Enabled Makes the control functional when this property is set to true (the default). Disables the control when this property is set to false. Note Disabling a control dims the control and makes it inactive. It does not hide the control.

Font Provides font information for the Web server control that you are declaring.

ForeColor The foreground color of the control. Note This property might not work for all controls in browsers earlier than Internet Explorer 4.0.

Height The control's height. Note This property might not work for all controls in browsers earlier than Internet Explorer 4.0.

TabIndex The control's position in the tab order. If this property is not set, the control's position index is 0. Controls with the same tab index are moved to according to the order in which they are declared in the Web page. Note This property only works in Microsoft Internet Explorer 4.0 and later.

ToolTip The text that appears when the user rests the mouse pointer over a control. Note The ToolTip property does not work in all browsers. Check with the browser for compatibility.

Width •The fixed width of the control. The possible units are: Pixel, Point, Pica, Inch, Mm, Cm, Percentage, Em•Ex Note The default unit is pixels. Not all browsers support every unit type.

Event Model• One of the key features of ASP.NET is that it

uses an event-based programming model.• An event handler is a method that

determines what actions are performed when an event occurs, such as when the user clicks a button or selects an item from a list.

• When an event is raised, the handler for that specific event is executed

Event Handlers• In the .NET Framework, all event handlers

have a specific method signature, that is, a specific return type and parameters.

• Event handlers are always void methods.• Event handlers always accept two

parameters:– an object parameter– an EventArgs parameter (or a subclass of

EventArgs, such as CommandEventArgs or ImageClickEventArgs).