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Web Technologies-II
Notes <body>
<form runat= “server”>
<asp:Button id= “button1” Text= “Click me!”
runat= “server” OnClick= “submit”/>
</form>
</body>
</html>
3.3.1 Generalities of ASP.NET Server Controls
All ASP.NET server controls, including HTML and Web controls plus any custom controls we
create or download, descend from the Control class. The class is defined in the System.Web.
UInamespace; it also is the foundation of all ASP.NET pages.
The Control class is declared as follows:
• Public class Control: IComponent, IDisposable, IParserAccessor,
• IUrlResolutionService, IDataBindingsAccessor,
• IControlBuilderAccessor, IControlDesignerAccessor,
• IExpressionsAccessor
The IComponent interface defines the way in which the control interacts with the other
components running in the common language runtime (CLR), whereas IDisposable implements
the common pattern for releasing managed objects deterministically.
3.3.2 Identifying a Server Control
The client ID of a control is generated from the value of the UniqueID property the truly server-
side identifier that ASP.NET generates for each control. The contents of the ClientID property
differ from UniqueID simply in that all occurrences of the dollar symbol ($), if any, are replaced
with the underscore (_). Dollar symbols in the UniqueID string are possible only If the control
belongs to a naming container different from the page.
ASP.NET generates the value for the UniqueID property based on the value of the ID property
that the programmer indicates. If no ID has been specified, ASP.NET auto-generates a name
such as _ctlX, where X is a progressive 0-based index. If the control’s naming container is the
host page, UniqueID simply takes the value of ID. Otherwise, the value of ID is prefixed with
the string representing the naming container and the result is assigned to UniqueID.
3.3.3 Naming Containers
A naming container is chiefly a control that acts as a container for other controls. In doing so,
the naming container generates a sort of virtual namespace so that ASP.NET roots the definite
ID of contained controls in the ID of the naming container. To fully understand the role and
importance of naming containers, consider the following example. Imagine we have a composite
control, such as a user control, that includes a child control like a button. Entirely wrapped by
the user control, the button is not directly accessible by the page code and cannot be given a
distinct and per-instance ID. In the end, the ID of the button is hard-coded in the outermost
control that creates it. What happens when two or more instances of the composite control are
placed on a page? Are we going to have two button child controls with the same ID? This is
exactly what will happen unless we configure the composite control to be a naming container.
The importance of naming containers does not end here. Imagine we have an instance of a
composite control named Control1. Imagine also that the embedded button is named Trigger.
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