vcsjones : ASP.NET

The AJAX Update Panel and Recursive Common Table Expressions

vcsjones — Thu, 19 Nov 2009 05:07:44 GMT

So my blog has become quiet again, but don’t worry! I’ve simply started pushing more of my posts toward our company blog. Check out my latest posts there:

The AJAX UpdatePanel: Is it your worst enemy?

Recursive Common Table Expressions

And from here on out are going to be a series on .NET 4.0.

ASP.NET AJAX 4.0 Client Template Rendering

vcsjones — Sun, 07 Jun 2009 06:24:00 GMT

Recently I have been dabbling with the ASP.NET 4.0 Framework. There were two things that immediately got my interest:

An actual new version of the CLR. More of come on that later…
AJAX 4.0

Now, I didn’t mean to say I was pumped an excited about it, but a certain element caught my attention, and that is Client Rendering. This basically, allows you to bind simple HTML to JSON or a simple JavaScript array. The idea is interesting, but I wasn’t sure how well it’d play.

To get started, I looked here: http://www.asp.net/learn/whitepapers/aspnet40/. This is a brief overview of the application. Not entirely informative, but it got me started. I fired up Visual Studio 2010 and began to tinker.

To start off, I wanted to build something simple. No JSON or Web Service calls, basics! I’m a slow learner. So, what exactly am I doing with this? Given the scenario where I have a JSON object with some information on it, I want to display it on the page. Now, there have been a few ways of doing this in the past. jQuery makes UI component for adapting JSON objects to tables, ordered elements, etc. The Microsoft implementation isn’t too different. It defines a binding for some sort of repeatable HTML element. Tables have repeating rows, unordered lists have repeating list items, etc. Unordered lists are pretty simple, so lets start there. Let’s say we are given a JSON object similar to this:

        1: var descriptions = [{ Name: "Foo", Description: "Foo is a great product." }, { Name: "Bar", Description: "Bar is OK, but not great."}];

Pretty simple. We have 2 objects in a collection with a Name and Description property. Now we want to show them in in an unordered list.

First, to get started, we need a ScriptManager in our page. This wires in all of Microsoft’s AJAX scripts for us.

       1: <asp:ScriptManager ID="MyScriptManager" runat="server">

       2:     <Scripts>

       3:         <asp:ScriptReference  Name="MicrosoftAjaxTemplates.js" />

       4:     </Scripts>

       5: </asp:ScriptManager>

I just plopped this right after the <body> tag. Notice the script reference is simply working on name. One of the new features of AJAX 4.0 is Microsoft broke apart the AJAX Framework JavaScript into different libraries. This allows you to selectively use the libraries you need and avoid large chunks of script you don’t need. In this case, we need the AJAX Templates script.

The AJAX functionality we will be using is an attached DataView. The scripting library works by attaching itself it an HTML element. In our case, it’s a unordered list. The attachment is done with a simple attribute on the element, sys:attach and then specify what you want to attach. Before we can go there, we need to tell our browser certain things, mainly namespaces. The body tag will contain certain namespace imports, similar to how WPF XAML imports namespaces. We want the DataView and the Sys namespace, so we’ll throw those in there:

       1: <body xmlns:sys="BLOCKED SCRIPTSys"

       2:     xmlns:dataview="BLOCKED SCRIPTSys.UI.DataView"

       3:     sys:activate="*">

There is one additional attribute, sys:activate that is in there. We’ll touch on that in a bit. So now we want to build our unordered list and attach a dataview to it. Let’s put together our unordered list and go through it.

       1: <ul id="descriptionsList" sys:attach="dataview" class="sys-template" dataview:data="{{ descriptions }}"> 

       2:     <li>    

       3:         <h3>{{ Name }}</h3>

       4:         <div>{{ Description }}</div>

       5:         <hr />

       6:     </li>

       7: </ul>

Notice the sys:attach attribute, and we are attaching a dataview to our unordered list. The other important attribute is the dataview:data. This is basically what data you want to bind to. Finally, we have a list item that is our “template” for what AJAX should use for all of the items. We denote a binding using double curly braces {{ }}. So {{ Name }} binds to the Name attribute in our JSON, etc. The dataview:data attribute is bound to our descriptions JSON object we declared.

There is one little piece left, and that is the class of sys-template. This is just a minor styling that sets display: none. This hides the entire element and the AJAX Framework will set the display properly once it has done fully loading all of the data and rendered it.

All together, it renders something like this:

All together, this was all of my source:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="ClientTemplates.aspx.cs" Inherits="DataControls.ClientTemplates" %>

       2: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

       3: <html xmlns="http://www.w3.org/1999/xhtml" >

       4: <head runat="server">

       5:     <style type="text/css">

       6:     .sys-template

       7:     {

       8:         display: none;

       9:     }

    </style>

    <script type="text/javascript">   1:     2:         var descriptions = [{ Name: "Foo", Description: "Foo is a great product." }, { Name: "Bar", Description: "Bar is OK, but not great."}];   3:     </script>

</head>

<body xmlns:sys="BLOCKED SCRIPTSys"

    xmlns:dataview="BLOCKED SCRIPTSys.UI.DataView"

    sys:activate="*">

    <form id="form1" runat="server">

        <div>

            <asp:ScriptManager ID="MyScriptManager" runat="server">

                <Scripts>

                    <asp:ScriptReference  Name="MicrosoftAjaxTemplates.js" />

                </Scripts>

            </asp:ScriptManager>

            <ul id="descriptionsList" sys:attach="dataview" class="sys-template" dataview:data="{{ descriptions }}"> 

                <li>    

                    <h3>{{ Name }}</h3>

                    <div>{{ Description }}</div>

                    <hr />

                </li>

            </ul>

        </div>

    </form>

</body>

</html>

And I didn’t write a single line in the code-behind, either.

This demonstrates the basic functionality of the binding. Next we’ll look at how to actually bind to dynamic data from a web service call, and manipulating the data.

Update: If you want to download a Visual Studio 2010 project, I’ve uploaded it here: http://bit.ly/VCWFd. It looks like Community Server is blocking some of the code snippets thinking it is XSS.

Managing IIS Pipeline Mode for Backward Compatibility

vcsjones — Fri, 26 Dec 2008 21:04:34 GMT

Ever since the induction of IIS 7, there came a cool new feature for developers to leverage called Integrated Pipeline. This feature in a short explanation closely couples ASP.NET and IIS more closely. It allows allows writing of IIS Modules in managed code, how neat is that? This also slightly changes the behavior of ASP.NET, such as introducing new events on the HttpApplication (Global.asax) and the event cycle. A classic example is where in Integrated mode you cannot access the current request using HttpContext.Current.Request during theApplication_Start event, which makes sense.

Now for obvious reasons this can break existing applications, and cannot be used for applications that will be installed in mixed environments, such as Server 2003 and Server 2008. Fortunately, IIS 7 make it easy to switch it back back to its old behavior using the Classic Pipeline by configuring the IIS AppPool. Most commonly, if you make a web-based product then your application will usually require Classic Pipeline to stay backwards compatible.

Even if you have a detailed instruction manual, this can be an easy step to miss - and results in some icky error messages. Wouldn't it be nice if you could display an nice error message to your customers that their pipeline is configured improperly?

Well fortunately there is a way to do that. Ironically, we will be using part of the Integrated Pipeline to get that accomplished with the help of an HttpModule.

What we will be doing is writing an HttpModule that will basically stop the current request, write out a friendly message that links to a Knowledge Base article, and only do this if our application is running in Integrated Pipeline. The module to get this done is pretty simple, we would write it like any other HttpModule. Here is the code for mine:

using System;
using System.Web;

namespace MyWebApplication
{
    public sealed class IisPiplineCheckModule : IHttpModule
    {
        public void Init(HttpApplication context)
        {
            context.BeginRequest += context_BeginRequest;
        }

        private void context_BeginRequest(object sender, EventArgs e)
        {
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.WriteFile(VirtualPathUtility.ToAbsolute("~/pipeline.htm"));
            HttpContext.Current.Response.End();
        }

        public void Dispose()
        {
        }
    }
}

As you can see, there is nothing particularly difficult. It just hooks into the BeginRequest event of the Application, and writes a file called pipeline.htm to the response stream and closes the response. Pretty simple, right?

Well the final trick is getting this to work only in Integrated Pipeline. Unusually, there is no easy way to do this with the .NET Framework (that I was able to find). However we will leverage the web.config to accomplish this.

For IIS 7, there is a new section in the web.config file called <system.webServer>. This is one of the sections that IIS 7 pays attention to. What we will do is introduce our module into IIS 7's Integrated Pipeline, but not into the old <httpModules> that has been existing for a long time. Let's look at our new section and examine it.

<system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <modules>
        <add preCondition="integratedMode" name="IisPipelineCheckModule" type="MyWebApplication.IisPiplineCheckModule,MyWebApplication" />
    </modules>
</system.webServer>

There are two interesting points here. The first is actually adding out module. Notice the preCondition. This is telling IIS 7 that our module should only be running in Integrated Pipeline by specifying the integratedMode flag. For the Type we just set the full namespace and class to our HttpModule and the assembly it is located in.

The second interesting point is that if you have standard HttpModules registered in the configuration/system.web/httpModules section IIS 7 will point out that there are modules in there that are not in the system.webServer configuration. We can, if we want, disable that through the validation element.

And ta-da, we now have a module that writes out a file, but only for Integrated Pipeline. You can customize the pipeline.htm file as much as you'd like. As far as I can tell, this is the only easy way to determine if your application is in Integrated or Classic Pipeline. The alternative is to WMI query the IIS metabase, which is a little more high risk and more complex.

Text Encoding (Part-1)

vcsjones — Mon, 19 May 2008 14:57:00 GMT

I was recently on the ASP.NET Forums and a member was asking, "How can I figure out the encoding of text?" and that got me thinking. There should be a reasonable way to do this, right? It's a useful thing to know. First, we need a little background on how text is encoded into bytes.

Long ago, back when 64K of memory was a big deal, characters took up a single byte. A byte ranges from 0 - 255, which allows us to support a total of 256 characters. Seems like plenty, no? English has 26, 52 for both cases, 62 with numbers, 92 with punctuation, and a few extra for line breaks, carriage returns, and tabs. So about 100, give or take a few. So what's the problem?

Well, this worked great and all, but other languages use different characters. The Cyrillic language by itself supports 33 letters. This is where encoding was introduced. In order to support multiple character sets, what each byte meant was determined by its encoding. This was done simply by knowing what encoding was used.

In today's world, where that average calculator has more memory than PCs did long ago, we now also use 2 byte encoding. That means that we can support 255 to the second power of characters, or 65,536. That is enough to support all languages in a single encoding, even though it takes up double the space. Problem solved, right? Not exactly.

While in this day and age we support double byte encoding, there are still other factors involved, such as the endianness (the order of the bytes. Big endian is backwards). Even then, there is still a lot of legacy data to support that is still single byte.

Say I give you a big binary chunk of data, and I tell you to convert it to text. How do you know which encoding is used? How do you even know which language it is in? I could be giving you a chunk of data using IBM-Latin. So how do we figure this out? Some smarts and process of elimination. Let's start with things we know.

All of the non single-byte encodings have what's called a Byte Order Mark, or BOM for short. This is a small amount of binary data pre-appended to the rest of the data that identifies which encoding it is. In .NET world, this is called the Preamble. Since the BOM is an ISO standard, it is always the same for the encoding used regardless if you are using .NET, Python, Ruby on Rails, etc. We can look at our data and see if the BOM can tell us.

To achieve this in .NET, we will be using most of the classes in the System.Text namespace. Specifically, the Encoding class. An instance of the encoding class has a method called GetPreamble(). Which will give us our BOM for that encoding. A BOM can be from 2 - 4 bytes, depending on the number of bytes used in the encoding. Remember when I said two bytes would be plenty? Well I fibbed, since there is an encoding called UTF-32 that supports 4 bytes (a whopping 4.2 billion character support).

We can then check our data to see if it starts with the BOM.

private static bool DataStartsWithBom(byte[] data, byte[] bom)
{
    bool success = data.Length >= bom.Length && bom.Length > 0;
    for (int j = 0; success && j < bom.Length; j++)
    {
        success = data[j] == bom[j];
    }
    return success;
}

So lets look at this method. This method takes our data, and a BOM, and determines if the data starts with the BOM. There are a few assumptions:

The data length is always greater than or equal to the BOM. If it is not, then there is no BOM at all, and we'll cover that in a bit.
The BOM's length is always greater than zero.

So let's put it to use (assume the local data is a byte[]):

foreach (EncodingInfo encodingInfo in Encoding.GetEncodings())
{
    Encoding encoding = encodingInfo.GetEncoding();
    byte[] bom = encoding.GetPreamble();
    if (DataStartsWithBom(data, bom))
        return encoding;
}

Here, we get all of the encodings that .NET knows of, and looks to see if our data byte array starts with that encodings BOM. If the encoding has no BOM, the DataStartsWithBom method will handle that with the bom.Length > 0 on the 3rd line. Once we know the encoding, we can decode it. You have to ensure that you don't actually try to decode the BOM itself:

encoding.GetString(data, bom.Length, data.Length - bom.Length);

Pretty straight forward so far, right?

Yes? OK let's move on. What about the case where we can't figure it out by the BOM? Most encodings don't have a BOM, only the UTF encodings do. ISO and OEM encodings, do not.

This is where it gets tricky, and where some pretty complex algorithms can come into play. The most important piece of information that you can have at this point, is knowing which language the text is in. With that, we can take a reasonable stab at which encoding is it.

.NET supports languages through the System.Globalization.CultureInfo class. This class will be very useful from here on forward. Let's take baby steps on attacking this problem, and while we don't know everything, we can use clues.

Each language has what's called an ANSI encoding. This a standard encoding used for that language assigned by the American National Standards Institute. The ANSI encoding is always a single byte encoding. This seems like a reasonable place to start.

We can get this Encoding by calling cultureInfoInstance.TextInfo.ANSICodePage. This only gives us the numeric code page (an identifier), but it's simple enough to create an instance of the Encoding class with the code page by calling Encoding.GetEncoding(int codePage).

How do I figure out the language? Chances are you know what language your users are using, or at least most of them. A case where you wouldn't know is screen-scraping. That can be figured out by looking at the encoding of the response. You can do that by looking at the ContentEncoding property off of the HttpResponse instance.

In most cases, this will probably work. By no means am I saying, "this will always work" in fact, there are a lot of bases that I haven't covered that I hope to in future blog posts. There are other code bits out there that do this already, and do a good job, but it's always good to know how it actually works, and fully understand the problem you are trying to solve.

So what'll be in part 2? How to decode text without knowing the language, and maybe in part two (part 3?) lossy decoding.

MVC Framework

vcsjones — Tue, 08 Apr 2008 04:33:11 GMT

The MVC framework is the new "hot" thing in the ASP.NET world for developers. As such, everyone has at least one blog entry about it. So, I think it's time I jumped on that ship. Though, I wanted to voice a few concerns with the MVC Framework, or at least how people perceive it.

The MVC design pattern is by no means new. It's been around since around 1979, and .NET is certainly not the first framework that supports the MVC Pattern, and nor is Microsoft's MVC Project the first for .NET. Spring is a very popular MVC solution for Java developers, and there is a .NET port of it as well. Though, I'm not here to give a history lesson either.

I often hang out at the ASP.NET Forums as a moderator and contributor. The MVC Framework is a pretty hot forum over there at the moment. Though after reading several posts, I can't help but get the feeling that several people aren't certain as to what the MVC design pattern is trying to solve.

So, at it's core, MVC is a design pattern that was originally used in SmallTalk-80. The original paper is up for interpretation, but at it's core theory, MVC's original goal was clean separation between layers of your application.

Yes, MVC gives you cool features like Routing, and a big bonus of Unit Testing. Anyone that has been using unit testing before knows that good separation of your code is important to achieve practical unit tests, especially those who also practice Test Driven Development; but the true goal of MVC (or MVP for that matter) is decoupling logic.

Some people originally made the claim that the current ASP.NET model (before the MVC project) was an MVC model. Well... mmmnnn...ooo. Not quite. It could be argued that it was, but the "not quite" was the event processing in .NET. The initial argument was that the event handles on controls coupled the code behind too tightly. A better solution would be to have the event handles work with a presentation model.

OK, I've been rambling on a little bit. What's my point (if any)? I suppose that Microsoft's MVC is pretty cool. I am a little perplexed as to why everyone got so excited about MVC since Microsoft announced they were providing a Framework when there are frankly, better and more mature MVC Frameworks around, and I'll circle back around to Spring for that one. Spring has been around since .NET 1.1, and since it is a Java port, they have a lot of experience from there, too. I get concerned that some people really aren't using MVC for the purpose of decoupling and improving their code; rather for some of its specialized features, such as Routing.

Though, in all honestly I tend to lean towards the MVP pattern myself. Not quite as popular, I still prefer it because the view is not as coupled with the model. A good MVP project is Stormwind NMVP.