20 ASP.Net Questions [Questions 6-10]
View Part One here
This article was created to be used as reference material for beginners through Intermediate developers. I have assembled 20 questions that I feel every developer should know when developing web applications and even Window’s application within the Visual Studio C# environment.
In this second installment of these articles we will answer questions six through ten in our list of 20 questions.
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What we will learn in this article:
- What is AJAX?
- What is View State?
- What is XML?
- What is XSLT?
- What is Captcha?
Getting started with our list - What is AJAX?
Let’s start with what is AJAX and what can I do with it?
ASP.NET AJAX is a free framework for quickly creating efficient and interactive Web applications that work across all popular browsers.
With ASP.NET AJAX you can:
- Create interfaces with AJAX components that can be reused.
- Upgrade your existing pages with AJAX controls.
- AJAX comes with support for all modern browsers
In a way and strictly speaking AJAX itself is not a technology, it mixes well-known programming techniques in a unique and uncommon way to enable programmers to develop Internet applications with a “WinForms” look and feel and a much more appealing user interface than we were able to develop in the past.
Before you begin any coding effort you will need to download the AJAX framework and install it onto our system in order to have the framework available to create your first AJAX web project. You can find out everything you need to know regarding AJAX at:
This web site is where you will find information on ASP.Net and AJAX, there are numerous articles, books, downloads and tutorials available on this site that will help guide you through the different options that AJAX offers for your web development.
You can find a helpful tutorial at ASP.NET that will help explain “How you get started with AJAX”. This video will help guide you through the process step by step and is very informative. You can find this video at:
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In order to use AJAX you will need to first install the “ASP.NET AJAX Extensions 1.0” and the “ASP.NET AJAX Control Toolkit” found on the ASP.NET web site mentioned earlier in the article. When you get to ASP.NET site you will need to click on the “AJAX” link to get to the home page for AJAX. Once you are on the home page click on the “Downloads” link to get to the ASP.NET AJAX Control Toolkit.
The download site is located at:
What is ViewState?
ViewState allows the state of objects (serializable) to be stored in a hidden field on the page. ViewState is transported to the client and back to the server, and is not stored on the server or any other external source. ViewState is used to retain the state of the server- side objects between postbacks.
Here are some notes on ViewState:
- ViewState is page-specific
- With ViewState you need only to rebind the controls when logic requires to
- Session is across all pages and ViewState is sort of like Session, but for only one page
- ViewState is sent to Client and returned on every post
ViewState is one of the ways that ASP.NET provides for us to save the data for later use in our applications. An important fact about ViewState is that it can only save the values for page level access. That means that if I save something on page one using ViewState I will not be able to access it on page two using the same technique. Because of this ViewState is only used to save the data values for the page level access which need to be maintained after any post back.
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Whenever you write anything into the ViewState object a hidden field will be created in the html. What this means is that ViewState is not as secure as Session, I am not saying that Session is totally secure, just that when you use Session the values are not written to the HTML for all users to view in their browsers and possibly decode.
Here is an example of how to access the ViewState:
What we have done is create a ViewState variable called ViewState[“Test”] and populating that variable with the string “This is a test of ViewState”. You can now access this variable anywhere within the current page level access.
What is XML?
XML is a markup language [Extensible Markup Language] that creates a standard for document creation similar to HTML. However, unlike HTML, the designer can design tags or elements that can be easy read and accessed. So XML is sort of like HTML which you are free to extend as needed, though you will need to stay within XML's parameters, when designing XML.
The idea behind XML and its standards is that currently there are many, many document formats and these formats are not always compatible with one another. The introduction of XML brings some standardization to these formats, so that everyone will be able to read all of the documents without any specific software.
XML's very strong typed syntax means that third party applications called "parsers" can easily be utilized to go into an XML structure and extract the data you are looking for. This makes XML almost like a 'transport layer' for file formats, where the file format designer doesn't have to be involved in the byte by byte construction of the data he or she is trying to represent.
Here is an example of a simple XML example:
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Here is an example of a more complex XML example:
As you can see XML is very broad and not something that can be explained within a paragraph or two. Hopefully this gives you a little more insight to what XML is and how it is used.
What is XSLT?
XSLT is a language with which you can transform one XML format to another. You are taking an input of an XML file and you are producing an output of a HTML document, web page, etc…
An XSLT document is of itself an XML document with the particular XSLT format applied. An XSLT document actually describes how to transform one XML document to another giving life to a set of data. A program type called an XML processor will do the actual work. It wants the XML and the XSLT document for input and then outputs the new XML document.
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Here is a snippet of some XSLT:
In the above example you will see as mentioned above that XSLT looks a lot like XML.
What is Captcha?
I found this blurb on the internet one day while researching Captcha:
CAPTCHA: Telling Humans and Computers Apart Automatically
A CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't:
http://www.captcha.net/ The official CAPTCHA site
It is a way to prevent hackers and spiders from infiltrating your system and submitting bogus information via your input forms. It is an ingenious way to handle this issue until they create an OCR application that can bypass this form of security. However, by the time that happens we will have found other ingenious ways to accomplish the separation of humans and computers.
Here is an example of a Captcha image:
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What we have Learned
We have completed the first ten questions of our list of twenty questions. We have delved into the various topics within our list and hopefully have given you a little insight to some of the answers you were looking for? In our next article in this series we will cover questions eleven through fifteen.
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