ASP.NET in a Nutshell

Handling Control Events

One of the most convenient aspects of the new ASP.NET Web Forms model is that it brings event-driven programming, popularized by Visual Basic, to the web world without all the kludginess of the late unlamented Visual Basic WebClasses. As explained in Chapter 3, ASP.NET has a number of built-in events at the page level for which you can write event handlers to execute code.

Moreover, most server controls expose one or more events for which you can write handlers. Table 5-7 shows a list of common events and the controls that support them. These events and controls are in addition to the standard events, such as Init, Load, PreRender, and UnLoad, that are inherited from the base Control class. For example, the Button server control exposes the Click and Command events. These events are both raised when the button is clicked, but while the Click event is usually used simply to handle the event for a single button, the Command event can be used to handle clicking on several buttons (so long as the buttons’ CommandName property is set). The CommandName property, along with an optional CommandArgument property, become properties of the CommandEventArgs object, which is passed as a parameter of the Command event handler. You can then examine the CommandName and CommandArgument properties within the event handler code to determine what action(s) to take.

Table 5-7. Control events

Event	Event type	Description	Controls
OnAdCreated	Change	Raised after creation ...