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Characteristics of ASP.NET Part III

Template engine

When first released, ASP.NET lacked a template engine. Because the .NET Framework is object-oriented and allows for inheritance, many developers would define a new base class that inherits from "System.Web.UI.Page", write methods there that render HTML, and then make the pages in their application inherit from this new class. While this allows for common elements to be reused across a site, it adds complexity and mixes source code with markup. Furthermore, this method can only be visually tested by running the application - not while designing it. Other developers have used include files and other tricks to avoid having to implement the same navigation and other elements in every page.

ASP.NET 2.0 introduced the concept of "master pages", which allow for template-based page development. A web application can have one or more master pages, which, beginning with ASP.NET 2.0, can be nested.^[15] Master templates have place-holder controls, called ContentPlaceHolders to denote where the dynamic content goes, as well as HTML and JavaScript shared across child pages.

Child pages use those ContentPlaceHolder controls, which must be mapped to the place-holder of the master page that the content page is populating. The rest of the page is defined by the shared parts of the master page, much like a mail merge in a word processor. All markup and server controls in the content page must be placed within the ContentPlaceHolder control.

When a request is made for a content page, ASP.NET merges the output of the content page with the output of the master page, and sends the output to the user.

The master page remains fully accessible to the content page. This means that the content page may still manipulate headers, change title, configure caching etc. If the master page exposes public properties or methods (e.g. for setting copyright notices) the content page can use these as well.

Other files

Other file extensions associated with different versions of ASP.NET include:

Extension	Required version	Description
asax	1.0	Global.asax, used for application-level logic [16]
ashx	1.0	custom HTTP handlers.
asmx	1.0	web service pages. From version 2.0 a Code behind page of an asmx file is placed into the app_code folder.
axd	1.0	when enabled in web.config requesting trace.axd outputs application-level tracing. Also used for the special webresource.axd handler which allows control/component developers to package a component/control complete with images, script, css etc. for deployment in one file (an 'assembly')
browser	2.0	browser capabilities files stored in XML format; introduced in version 2.0. ASP.NET 2 includes many of these by default, to support common web browsers. These specify which browsers have which abilities, so that ASP.NET 2 can automatically customize and optimize its output accordingly. Special .browser files are available for free download to handle, for instance, the W3C Validator, so that it properly shows standards-compliant pages as being standards-compliant. Replaces the harder-to-use BrowserCaps section that was in machine.config and could be overridden in web.config in ASP.NET 1.x.
config	1.0	web.config is the only file in a specific Web application to use this extension by default (machine.config similarly affects the entire Web server and all applications on it), however ASP.NET provides facilities to create and consume other config files. These are stored in XML format.
cs/vb	1.0	Code files (cs indicates C#, vb indicates Visual Basic). Code behind files (see above) predominantly have the extension ".aspx.cs" or ".aspx.vb" for the two most common languages. Other code files (often containing common "library" classes) can also exist in the web folders with the cs/vb extension. In ASP.NET 2 these should be placed inside the App_Code folder where they are dynamically compiled and available to the whole application.
dbml	3.5	LINQ to SQL data classes file
master	2.0	master page file. Default file name is Master1.master
resx	1.0	resource files for internationalization and localization. Resource files can be global (e.g. messages) or "local" which means specific for one aspx or ascx file.
sitemap	2.0	sitemap configuration files. Default file name is web.sitemap
skin	2.0	theme skin files.
svc	3.0	Windows Communication Foundation service file
edmx	3.5	ADO.NET Entity Framework model

Directory structure

In general, the ASP.NET directory structure can be determined by the developer's preferences. Apart from a few reserved directory names, the site can span any number of directories. The structure is typically reflected directly in the URLs. Although ASP.NET provides means for intercepting the request at any point during processing, the developer is not forced to funnel requests through a central application or front controller.

The special directory names (from ASP.NET 2.0 on) are:

App_Code 

This is the "raw code" directory. The ASP.NET server automatically compiles files (and subdirectories) in this folder into an assembly which is accessible in the code of every page of the site. App_Code will typically be used for data access abstraction code, model code and business code. Also any site-specific http handlers and modules and web service implementation go in this directory. As an alternative to using App_Code the developer may opt to provide a separate assembly with precompiled code.

App_Data 

default directory for databases, such as Access mdb files and SQL Server mdf files. This directory is usually the only one with write access for the application.

App_LocalResources 

E.g. a file called CheckOut.aspx.fr-FR.resx holds localized resources for the French version of the CheckOut.aspx page. When the UI culture is set to french, ASP.NET will automatically find and use this file for localization.

App_GlobalResources 

Holds resx files with localized resources available to every page of the site. This is where the ASP.NET developer will typically store localized messages etc. which are used on more than one page.

App_Themes 

Adds a folder that holds files related to themes which is a new ASP.NET feature that helps ensure a consistent appearance throughout a Web site and makes it easier to change the Web site’s appearance when necessary.

App_WebReferences 

holds discovery files and WSDL files for references to web services to be consumed in the site.

Bin 

Contains compiled code (.dll files) for controls, components, or other code that you want to reference in your application. Any classes represented by code in the Bin folder are automatically referenced in your application.