ASP .NET Web Developer s Guide - Mesbah Ahmed, Chris Garrett

170Chapter 3 • ASP Server Controls

;VS.NET follows Code-Behind methodology for ASP.NET development.

Using HTML Server Controls

;HTML controls are not programmable at the server-side.Their values do not persist.The HTML server controls have been developed both of these problems.The ASP Engine maps the HTML server controls to HTML controls before a page is sent to the client.

;Certain HTML server controls can be bound to a data source. For example, if a list box is bound to a data source, it is automatically loaded with the data in the data source.This is known as data binding.

;If necessary, we can mix HTML server controls and Web server controls in the same page.

Using ASP.NET Web Controls

;These controls are similar to the HTML server controls; however, these controls have a richer and more consistent object model.

;Some of the new and powerful Web controls are: Repeater, DataList, and DataGrid.These are also known as Data-Bound Templated control.These controls allow displaying data from a data source almost automatically.The DataGrid and DataList controls allow data selection and data editing.

;A validation control enables us to validate an input and display an error message if necessary.

;There are six Validation Controls: RequiredFieldValidator, RangeValidator, CompareValidator, RegularExpressionValidator, CustomValidator, and ValidationSummary.

;The Validation controls automatically generates client-side and serverside validation code. If necessary, you can also develop custom validation functions.

Creating Custom ASP Server User Controls

;Custom controls are similar to ActiveX controls, except that these are much easier to develop.

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;There are two types of custom controls: Web User Controls and Web Custom Controls.

;A custom control can be used exactly like any other Web server controls.

Frequently Asked Questions

The following Frequently Asked Questions, answered by the authors of this book, are designed to both measure your understanding of the concepts presented in this chapter and to assist you with real-life implementation of these concepts. To have your questions about this chapter answered by the author, browse to www.syngress.com/solutions and click on the “Ask the Author” form.

Q:How much will ASP syntax change during the transition from Beta 2 to the final version?

A:Microsoft has “predicted” that there will be no syntactical changes.This should be good news to developers who were faced with some confusion when certain classes were dropped, added, and modified during the last transition from Beta 1 to Beta 2.

Q:What happens to the existing ASP applications when the .Net Beta 2 SDK is installed and .aspx files enter the picture?

A:Nothing! The good news is that files extensions used by ASP (.asp, .asa, etc.) are completely separate from the ones used by ASP.NET (.aspx, .asax, .ascx, etc.) and do not override each other even in the same directory.The bad news is that settings made in the global.asa file are not accessible to those made in the global.asax file, and therefore you have to redo some setting to get some consistency.

Q:Are paths such as HREFs in user controls relative to the user control or to the host page that they are in?

A:The paths are relative to the user control and not to the host page.This makes it much easier for the user control to find things irrespective of what direc-

tory the calling .aspx file is. Another interesting feature in paths is that you can use the “~” to represent the application root to shortcut the use of the Request Application path.This really makes the building of large Web sites more manageable.

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Chapter 4

Configuring ASP.NET

Solutions in this chapter:

■Overview of ASP.NET Configuration

■Uses for a Configuration File

■Anatomy of a Configuration File

;Summary

;Solutions Fast Track

;Frequently Asked Questions

173

174 Chapter 4 • Configuring ASP.NET

Introduction

As applications became more complex and started offering more configurable features, a natural progression was to use configuration files to store these values. It has since become a required feature of any application to support the use of configuration files to control various aspects of itself and to avoid hard-coding of variable data. Most Windows applications support this with the use of .ini files or entries in the Windows registry. ASP.NET includes this support by the use of machine.config and web.config files.These files are standard text files written using XML formatting and can be edited with any text editor such as Notepad or an XML parser.With the use of these files, ASP.NET provides the ability to modify many standard settings used within Web applications as well as allowing the creation of custom settings.

The configuration of a given Web application is computed in a hierarchical manner when the application is first accessed and then cached to speed up future references to the configuration. ASP.NET then monitors the configuration files for any changes, and if a change is detected, the cached configuration is flushed and recomputed.

In this chapter, we will go over the way ASP.NET uses its configuration files and how we can best take advantage of this feature.We will also discuss the application, system, and security aspects of the configuration files and work through the creation of a web.config file.

Overview of ASP.NET Configuration

The configuration files used by ASP.NET are processed in a hierarchical manner. This means that the files located at a higher level of the hierarchy can override the options set within each file. An exception to this rule is provided to allow for locking down some settings.This exception uses the allowOverride attribute and the <location> tag to lock down the settings.The use of this option is explained in the “Anatomy of a Configuration File” section later in this chapter.

The machine.config file is used on a per-server basis and controls the base configuration of ASP.NET on the system.The machine.config is located in the

C:\winnt\Microsoft.NET\Framework\version\CONFIG\ directory and is the highestlevel configuration file.The web.config file can be located in your root application directory as well as in any subdirectories below it in order to set Web application specific configuration. If a value is not explicitly defined in a lower level configuration file and is defined in a higher-level file, the value will be

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inherited from the higher level configuration file.This process is outlined in Figure 4.1.

Figure 4.1 Configuration Inheritance

Figure 4.1 illustrates several important points regarding ASP.NET’s use of configuration files. Let’s walk through what this illustration shows.

First, the order in which the configuration files are processed is shown.The machine.config file is processed first. Any values specified within the machine

.config file are inherited throughout every ASP.NET application on your Web server.The web.config file in each consecutive subdirectory is then processed with each lower-level file overriding the configuration files above it unless otherwise instructed.

Secondly, if a value is not explicitly defined in a lower-level configuration file, the value is inherited from the higher-level file.This is a very important feature to keep in mind as values set in a higher-level file may cause problems with an application stored at lower level.

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176 Chapter 4 • Configuring ASP.NET

SECURITY ALERT!

With the standard ASP.NET machine.config file, all configuration files are secured and cannot be downloaded by a client system. This allows for some protection of critical information such as user IDs and passwords for DSN sources, but keep in mind that any system can be hacked with enough time and effort. Always keep security in mind when planning your Web application.

Debugging…

Configuration Hierarchy

An important note to keep in mind when planning your usage of configuration files is the hierarchical manner in which ASP.NET computes the effective configuration of your application. When ASP.NET reads in the web.config in each consecutive directory, it goes from each physical subdirectory to the next.

Virtual directories cause this processing to occur somewhat differently. Let us assume as an example that you have a web.config file physically located in E:\wwwroot\mainapp and have the virtual directory app assigned to this directory.

Later you add another application in E:\wwwroot\mainapp\subapp and assign the virtual directory subapp to this directory. If you access your sub-application by using http://localhost/app/subapp/myapp.aspx, the settings in the machine.config as well as the web.config stored in the mainapp are applied. However, if your sub-application is accessed via http://localhost/subapp/myapp.aspx, only the settings configured in the machine.config are applied.

This caveat of configuration inheritance is very important to keep in mind when designing your virtual directory structure. If structured incorrectly, your applications could experience errors, or could fail.

Finally, we can see how the use of the allowOverride attribute affects an application’s configuration.The default value for the allowOverride attribute is true, which allows any lower level configuration file to override the configuration specified in a higher-level file.You can change this behavior by setting the allowOverride attribute

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to false, which prevents lowerlevel configuration files from overriding configuration options set at a higher level. If a lower-level configuration file attempts to override this setting, an error will occur.We will go into more detail on the allowOverride attribute for the <location> tag later in the chapter.

Uses for a Configuration File

When examining the uses for ASP.NET’s configuration files, we must look at the machine.config file as well as the web.config file.The main difference between these two files is that the machine.config file is applied system-wide while the web.config is applied to each application based on the inheritance rules. Each configuration option set within the machine.config file is applied to every application and by using the allowOverride attribute in conjunction with the <location> tag; you can prevent individual web.config files from overriding these settings.

When ASP.NET is initially installed, a default machine.config file is set up for your system with the standard configuration section handlers used within ASP.NET as well as many other configuration items.You can edit this default file to tailor your ASP.NET configuration to your requirements.You can also configure the same options in the lower-level web.config files in order to give you more granular control over individual applications.

You can configure almost all functional items of ASP.NET through the configuration files.The options available to you using the default ASP.NET machine.config file include everything from browser compatibility options to secure authentication options.Table 4.1 details the standard tags available through the ASP.NET configuration files; however, you can define additional tags by defining new configuration section handlers.

Table 4.1 Standard Configuration Tags

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178 Chapter 4 • Configuring ASP.NET

Table 4.1 Continued

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You can break up these standard configuration tags into three main configuration groups:

■ASP.NET Application Configuration

■ASP.NET System Configuration

■ASP.NET Security Configuration

Each standard tag in Table 4.1 has been categorized as belonging to one of these three configuration groups, and we will review each option and its function in the following sections. Many of these tags do overlap between the configuration groups, but this breakdown serves as a general guideline for defining your configuration.

Application Configuration

The application configuration tags are generally used to control application-spe- cific settings.You can set all of these tags either within the machine.config file or a web.config file at any level.

Setting Static Variables Using the <appSettings> Tag

The <appSettings> tag supports only two attributes, a key and a value.This setting enables you to set static variables for your application. One excellent use for this configuration setting is to set all of your application specific variables in a single location.This gives you the ability to completely control your application

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