Asp.NET Interview Questions

.NET SDK can be obtained here.

(You have to install the Microsoft .NET Framework Version 1.1 Redistributable Package before installing the .NET SDK.)

• Microsoft provides Visual Studio 2005 Express Edition Beta for free. Of particular interest to the ASP.NET developers would be the Visual Web Developer 2005 Express Edition Beta 2 available as a free download.
• The ASP.NET Web Matrix Project (supported by Microsoft) is a free IDE for developing ASP.NET applications and is available here.
• There is also a free open-source UNIX version of the Microsoft .NET development platform called Mono available for download here.
• Another increasingly popular Open Source Development Environment for .NET is the #develop (short for SharpDevelop) available for download here.

ASP.NET is a part of the .NET framework which was released as a software platform in 2002.

ASP.NET 2.0, Visual Studio 2005 (Whidbey), Visual Web Developer 2005 Express Edition are the next releases of Microsoft's Web platform and tools. They have already been released as Beta versions. They are scheduled to be released in the week of November 7, 2005.

Namespaces are logical groupings of names used within a program. There may be multiple namespaces in a single application code, grouped based on the identifiers’ use. The name of any given identifier must appear only once in its namespace.

• Windows (default)
• Forms
• Passport
• None (Security disabled)

Common Language Runtime (CLR) is a run-time environment that manages the execution of .NET code and provides services like memory management, debugging, security, etc. The CLR is also known as Virtual Execution System (VES).

The CLI is a set of specifications for a runtime environment, including a common type system, base class library, and a machine-independent intermediate code known as the Common Intermediate Language (CIL). (Source: Wikipedia.)

• Init()
• Load()
• PreRender()
• Unload()

An assembly is a collection of one or more files and one of them (DLL or EXE) contains a special metadata called Assembly Manifest. The manifest is stored as binary data and contains details like versioning requirements for the assembly, the author, security permissions, and list of files forming the assembly. An assembly is created whenever a DLL is built. The manifest can be viewed programmatically by making use of classes from the System.Reflection namespace. The tool Intermediate Language Disassembler (ILDASM) can be used for this purpose. It can be launched from the command prompt or via Start> Run.

In order to replace a COM component on a live dedicated server, it was necessary to stop the entire website, copy the new files and then restart the website. This is not feasible for the web servers that need to be always running. .NET components are different. They can be overwritten at any time using a mechanism called Shadow Copy. It prevents the Portable Executable (PE) files like DLLs and EXEs from being locked. Whenever new versions of the PEs are released, they are automatically detected by the CLR and the changed components will be automatically loaded. They will be used to process all new requests not currently executing, while the older version still runs the currently executing requests. By bleeding out the older version, the update is completed.

DLL hell is the problem that occurs when an installation of a newer application might break or hinder other applications as newer DLLs are copied into the system and the older applications do not support or are not compatible with them. .NET overcomes this problem by supporting multiple versions of an assembly at any given time. This is also called side-by-side component versioning.

Web services are programmable business logic components that provide access to functionality through the Internet. Standard protocols like HTTP can be used to access them. Web services are based on the Simple Object Access Protocol (SOAP), which is an application of XML. Web services are given the .asmx extension.

Windows Forms is employed for developing Windows GUI applications. It is a class library that gives developers access to Windows Common Controls with rich functionality. It is a common GUI library for all the languages supported by the .NET Framework.

When an action occurs (like button click), the page containing all the controls within the <FORM... > tag performs an HTTP POST, while having itself as the target URL. This is called Postback.

Server side scripting means that all the script will be executed by the server and interpreted as needed. Client side scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in VBScript or JavaScript. Since the code is included in the HTML page, anyone can see the code by viewing the page source. It also poses as a possible security hazard for the client computer.

• @ Page directive
• @ Import directive
• @ Implements directive
• @ Register directive
• @ Assembly directive
• @ OutputCache directive
• @ Reference directive

Code-Behind is a concept where the contents of a page are in one file and the server-side code is in another. This allows different people to work on the same page at the same time and also allows either part of the page to be easily redesigned, with no changes required in the other. An Inherits attribute is added to the @ Page directive to specify the location of the Code-Behind file to the ASP.NET page.

Inline code is written along side the HTML in a page. There is no separate distinction between design code and logic code. Code-behind is code written in a separate file and referenced by the .aspx page.

• RequiredFieldValidator
• RangeValidator
• CompareValidator
• RegularExpressionValidator
• CustomValidator
• ValidationSummary

Data binding is a way used to connect values from a collection of data (e.g. DataSet) to the controls on a web form. The values from the dataset are automatically displayed in the controls without having to write separate code to display them.

The DataGrid control in ASP.NET enables easy paging of the data. The AllowPaging property of the DataGrid can be set to True to perform paging. ASP.NET automatically performs paging and provides the hyperlinks to the other pages in different styles, based on the property that has been set for PagerStyle.Mode.

All user input data validation should occur on the server and minimally on the client-side, though it is a good way to reduce server load and network traffic because we can ensure that only data of the appropriate type is submitted from the form. It is totally insecure. The user can view the code used for validation and create a workaround for it. Secondly, the URL of the page that handles the data is freely visible in the original form page. This will allow unscrupulous users to send data from their own forms to your application. Client-side validation can sometimes be performed where deemed appropriate and feasible to provide a richer, more responsive experience for the user.

• Response.Redirect: This tells the browser that the requested page can be found at a new location. The browser then initiates another request to the new page loading its contents in the browser. This results in two requests by the browser.
• Server.Transfer: It transfers execution from the first page to the second page on the server. As far as the browser client is concerned, it made one request and the initial page is the one responding with content. The benefit of this approach is one less round trip to the server from the client browser. Also, any posted form variables and query string parameters are available to the second page as well.