Extending ASP.NET

As we mentioned earlier in the chapter, ASP.NET is an extensible Web application development platform. The extensibility of ASP.NET ”a feature in and of itself ”results from the modular design and componentized architecture of ASP.NET. As a component developer, you can create components that fit into different levels of ASP.NET to customize various aspects of the request/response cycle. These custom components take the form of custom controls or new HTTP handlers and HTTP modules.

The primary focus of the book is to explain the control architecture and to enable you to develop custom controls for use in the ASP.NET page framework. Controls form the building blocks that are used to create the user interface of all ASP.NET Web applications. They provide a run-time programming model and a design-time experience that are used by the page developer and the page designer. They contain the functionality to render themselves as part of the response generated by the page when it is requested . Server controls represent the most widely used components in an ASP.NET Web application. You can create new controls and extend or combine existing controls to implement and encapsulate new behavior, functionality, and user interface elements. Part II of the book provides an overview of control authoring, and Part III provides an in-depth look at control development.

ASP.NET allows you to develop and register custom HTTP handlers and HTTP handler factories to process new file extensions, substitute a built-in HTTP handler, and customize the processing of specific URLs. Chapter 19 describes the details of implementing and registering custom HTTP handlers.

Finally, ASP.NET allows you to develop and register custom HTTP modules to participate in its pipeline architecture and perform preprocessing and postprocessing of all incoming requests . As a component developer, you can develop custom modules that add extra processing for each request, substitute one of the built-in modules, or generate content and content headers into the response stream.