Chapter 4 ASP.NET Core Server Controls

Overview

ASP.NET pages are made of code, markup tags, literal text, and server controls. Based on the request, the server controls generate the right markup language. The ASP.NET runtime combines the output of all controls and serves the client a page to display in a browser. The programming richness of ASP.NET springs from the wide library of server controls that covers the basic tasks of HTML interaction for example, collecting text through input tags as well as more advanced functionalities such as calendaring, menus, tree views, and grid-based data display.

The runat attribute is key to ASP.NET control programming. If a tag in the .aspx source is declared without the runat attribute, it is considered plain text and is output verbatim. Other wise, the contents of the tag are mapped to a server control and processed during the page life cycle. Back in Chapter 1, we identified two main families of server controls HTML server controls and Web server controls. HTML controls map to HTML tags and are implemented through server-side classes whose programming interface faithfully represents the standard set of attributes for the corresponding HTML tag. Web controls, in turn, are a more abstract library of controls in which adherence of the proposed API to HTML syntax is much less strict. As a result, Web and HTML controls share a large common subset of functionalities and, in spite of a few exceptions, we could say that Web controls, functionally speaking, are a superset of HTML controls. Web controls also feature a richer development environment with a larger set of methods, properties, and events and participate more actively in the page life cycle.

As we'll see in more detail in the following pages, a second and more thoughtful look at the characteristics of the server controls in ASP.NET reveals the existence of more than just two families of controls. In real-world ASP.NET applications, you'll end up using controls from at least the following functional categories: HTML controls, core Web controls, validation controls, data-bound controls, user controls, mobile controls, and custom controls. Validation controls are a special subset of Web controls and deserve to be treated in a separate section. Data-bound controls are not a category per se, with features that make them different from HTML or Web controls. Data binding, instead, refers to the control's capability of connecting some of its properties to particular data sources. Hence, data-bound controls fall into any of the previously listed groups of server controls, but they deserve a section of their own because of their frequent use. User controls are visual aggregates of existing Web and HTML controls that appear as individual, encapsulated, programmable controls to external callers. Mobile controls are used when creating Web applications that target mobile devices. Custom controls refer to server controls you create that derive from a base control class.

In this chapter, we'll cover HTML controls, Web controls, and validation controls. Data-bound controls will be covered in Chapter 9. User controls, mobile controls, and custom controls will find their place in my other recent book, Programming Microsoft ASP.NET 2.0 Applications: Advanced Topics (Microsoft Press, 2005), which is written for advanced users as a companion book to this one.