AjaxGuide

AJAX .Net Wrapper usage guide

AJAX .Net Wrapper usage guide. 1

Background. 1

How it works - Overview. 2

Initial Setup. 2

Setting up the HttpHandler 2

Setting up the Page. 3

Creating the Server-Side Functions 4

Making our client-side call 5

Dealing with Types 6

Returning complex types 6

Custom Converters 8

Miscellaneous 8

Registering functions in another class 8

How the proxy really works 8

Returning Unicode characters 9

SessionState. 9

Conclusion. 10

Background

Asynchronous JavaScript and XML (AJAX) has recently become the craze thanks, in no small part, to Google’s usage of it in Google Suggest as well as Google Maps. In ASP.Net terms, AJAX allows server-side processing to occur without requiring postback, thus enabling clients (browsers) with rich server-side capabilities. In other words it provides a framework for asynchronously dispatching and processing requests and responses from the server. AJAX leverages a number of existing technologies, which aren't particularly new, however fondness for what these technologies have to offer (collectively, they are AJAX) has recently soared.

Enter Michael Schwarz's AJAX .Net wrapper which allows ASP.Net developers to quickly and easily deploy pages capable of easily capitalizing on AJAX. Users should be cautioned that the wrapper is early in development, and as such isn't fully matured.

It should be pointed out that technologies such as AJAX are very likely going to lead to violations of layered architectures (N-Tier). My opinion is that AJAX increases the likelihood that the presentation logic layer (or worse, the business layer) will leak into the presentation layer. Strict architects, like me, might cringe at this notion. I feel that even if AJAX is used in a manor which slightly violates layer boundaries, the payoffs are well worth it. Of course, that's something you'll need to look at for your specific project and environment.

To learn more about AJAX, visit: http://en.wikipedia.org/wiki/AJAX http://www.adaptivepath.com/publications/essays/archives/000385.php

How it works - Overview

AJAX relies on a broker to dispatch and process requests to and from the server. For this task, the .Net wrapper relies on the client-side XmlHttpRequest object. The XmlHttpRequest object is well supported by most browsers, making it the solution of choice. Since the goal of the wrapper is to hide the implementation of XmlHttpRequest, we'll forgo any detailed discussion about it.

The wrapper itself works by marking .Net functions as AJAX methods. Once marked, AJAX creates corresponding JavaScript functions which can be called client-side (liky any JavaScript functions) and that serve as proxies, using XmlHttpRequest. These proxies map back to the server-side function.

Complicated? It isn't. Let's look at a simplified example. Given the .Net function:

'VB.Net public function Add(firstNumber as integer, secondNumber as integer) as integer return firstNumber + secondNumber end sub

//C# public int Add(int firstNumber, int secondNumber) { return firstNumber + secondNumber; }

The AJAX .Net wrapper will automatically create a JavaScript function called "Add" which takes two parameters. When this function is called using JavaScript (on the client), the request will be passed to the server and the return value back to the client.

Initial Setup

We'll first go through the steps of "installing" the .dll for use in your project. If you know how to add a reference to a .dll file, skip this section.

First, if you don’t already have it, download the latest version of AJAX. Unzip the downloaded file and place the ajax.dll within a ref folder of your project. In Visual Studio.Net, right click the "References" node in the Solution Explorer and select Add Reference. In the newly opened dialog, click Browse and navigate to the ref/ajax.dll file. Click Open followed by Ok. You are now ready to start programming with the AJAX .Net wrapper.

If you’re having difficulty setting up the reference, check out: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon/html/vbtskaddingremovingreferences.asp

Setting up the HttpHandler

The first step necessary to make everything work is to set up the wrapper's HttpHandler in the web.config. Without going into detailed explanation of what and how HttpHandlers work, it's sufficient to know that that they are used to process ASP.Net requests. For example, all requests for *.aspx pages are handled by the System.Web.UI.PageHandlerFactory class. Similarly we'll make all requests to ajax/*.ashx handled by the Ajax.PageHandlerFactory:

verb="POST,GET" path="ajax/*.ashx" type="Ajax.PageHandlerFactory, Ajax" /> ...

The above code basically tells ASP.Net that any requests made that match the specified path (ajax/*.ashx) are to be handled by Ajax.PageHandlerFactory, instead of the default handler factory. You don’t need to create an ajax subdirectory, this is a mythical directory simply used so that other HttpHandlers can use the .ashx extension with their own made-up subdirectories.

Setting up the Page

We are now ready to start coding. Create a new page, or open an existing one and in the code behind file, add the following code in the Page_Load event:

'vb.net Public Class Index Inherits System.Web.UI.Page Private Sub Page_Load(sender As Object, e As EventArgs) Handles MyBase.Load Ajax.Utility.RegisterTypeForAjax(GetType(Index)) '... end sub '... End Class

//C# public class Index : System.Web.UI.Page{ private void Page_Load(object sender, EventArgs e){ Ajax.Utility.RegisterTypeForAjax(typeof(Index)); //... } //... }

The call to RegisterTypeForAjax emits the following JavaScript on the page (alternatively, you could manually place the following two lines on the page):

Where the bolded parts have the following meaning:

NAMESPACE.PAGECLASS	The namespace and class of the current page (this will typically be the value of the Inherits attribute in the @Page directive)
ASSEMBLYNAME	The name of the assembly the current page is part of (this will typically be the name of your project)

Bellow is a sample output for the sample.aspx page in an AjaxPlay project:

<%@ Page Inherits="AjaxPlay.Sample" Codebehind="sample.aspx.cs" ... %> id="Form1" method="post" runat="server"> ...

You can test that everything is working properly by manually navigating to the src paths in your browser (view source and copy and paste the paths). If both paths output some (seemingly) meaningless text, you’ve done well so far. If they’re outputting nothing or ASP.Net errors, something was improperly done.

Even if you don’t know how HttpHandlers work, the above should be understandable. Via the web.config, we’ve made sure that all requests that go to ajax/*.ashx are processed by the custom handler. Obviously, the two script tags will be processed by this custom handler.

Creating the Server-Side Functions

We’ll now create a server-side function that’ll be asynchronously be available from a client-side call. Since not all return types are currently supported (don’t worry, upcoming versions will build on what’s currently there), we’ll stick with our simple ServerSideAdd functionality. In the code behind file, add the following method to your page class:

'VB.Net _ Public Function ServerSideAdd (byval firstNumber As Integer, byval secondNumber As Integer) As Integer Return firstNumber + secondNumber End Function

//C# [Ajax.AjaxMethod()] public int ServerSideAdd(int firstNumber, int secondNumber) { return firstNumber + secondNumber; }

Note that the functions have the Ajax.AjaxMethod attribute set. The attribute serves to tell that wrapper to create JavaScript proxies for these methods so that they might be called client-side.

Making our client-side call

The last step is to call the function using JavaScript. The AJAX wrapper took care of creating a JavaScript function called Sample.ServerSideAdd function which takes two parameters. For the most basic functionality, all we need to do is call the method and pass two numbers:

<%@ Page Inherits="AjaxPlay.Sample" Codebehind="sample.aspx.cs" ... %> id="Form1" method="post" runat="server">

Of course, we’ll want to use this powerful capability for more than simply alerting the user. That’s why all client-side proxies (such as the JavaScript Sample.ServerSideAdd function), also accept an additional property. The property is the callback function called in order to process the response:

Sample.ServerSideAdd(100,99, ServerSideAdd_CallBack); function ServerSideAdd_CallBack(response){ if (response.error != null){ alert(response.error); return; } alert(response.value); }

We can see from the above code that we’ve specified an extra parameter. ServerSideAdd_CallBack (also shown above) is the client-side function used to process the response from the server. The callback function receives a response object which exposes three key properties:

value	The actual return value (be it a string, custom object or dataset) of the server-side function.
error	An error message, if any.
request	The raw response from the xml http request.
context	A context object.

First we check the error value to see if any errors occurred. You can easily play with the error property by throwing an exception in the server-side function. Then, in this simplified case, we alert the value. The request property can be used to get additional information (see box bellow).

To learn more about the Xml Http request, check out the following link dump: http://www.quirksmode.org/blog/archives/2005/02/xmlhttp_linkdum.html

Dealing with Types

Returning complex types

The Ajax wrapper is capable of handling more than just the integer our ServerSideAdd function returned. It currently supports integers, strings, double, booleans, DateTime, DataSets and DataTables, as well as the primitive types of custom classes and arrays. All other types have their ToString values returned.

Returned DataSets work much like real .Net DataSet. Given a server side function which returns a DataSet, we could display the contents client side via:

Ajax can also return custom classes. All that is required is that the class be marked with the Serializable attribute. Given the following class:

[Serializable()] public class User{ private int _userId; private string _firstName; private string _lastName; public int userId{ get { return _userId; } } public string FirstName{ get { return _firstName; } } public string LastName{ get { return _lastName; } } public User(int _userId, string _firstName, string _lastName){ this._userId = _userId; this._firstName = _firstName; this._lastName = _lastName; } public User(){} [AjaxMethod()] public static User GetUser(int userId){ //Replace this with a DB hit or something :) return new User(userId,"Michael", "Schwarz"); } }

We would register the GetUser proxy via a call to the RegisterTypeForAjax:

private void Page_Load(object sender, EventArgs e){ Utility.RegisterTypeForAjax(typeof(User)); }

Allowing us to asynchronously call the GetUser in client-side code with code such as:

The value returned in the response is actually an object which exposes the same properties as a server-side object (FirstName, LastName and UserId).

Custom Converters

As we’ve seen, the Ajax .Net wrapper is able to deal with many different .Net types. However, aside from a handful of .Net classes and the built-in types, the wrapper simply calls ToString() on anything it can’t properly return. To get around this, the Ajax .Net wrapper allows developers to create object converters which can be used to smoothly communicate complex objects between the server and the client.

This guide will be updated with additional information on custom converters shortly (sorry).

Miscellaneous

Registering functions in another class

In the above example, our server-side functions resided within the code behind of the executing page. However, there’s no reason why these functions can’t be in a separate class file. Remember, the way the wrapper works is to find all methods within the specified class that have the Ajax.AjaxMethod. The class in question is specified via the second script tag. Using Ajax.Utility.RegisterTypeForAjax we can specify any class we want. For example, it would be reasonable to keep our server-side functions in a separate class:

Public Class AjaxFunctions _ Public Function Validate(username As String, password As String) As Boolean 'do something 'Return something End Function End Class

We could have the Ajax wrapper create proxies for this class by specifying this class’s type instead of the pages:

'Vb.Net Private Sub Page_Load(sender As Object, e As EventArgs) Handles MyBase.Load Ajax.Utility.RegisterTypeForAjax(GetType(AjaxFunctions)) '... End Sub

//C# private void Page_Load(object sender, EventArgs e){ Ajax.Utility.RegisterTypeForAjax(typeof(AjaxFunctions)); //... }

Remember, the client-side proxy takes the name of .. Therefore, if our ServerSideAdd function was located in the fictional AjaxFunctions class above, our client-side call would be: AjaxFunctions.ServerSideAdd(1,2)

How the proxy really works

The second script tag generated by the Ajax utility (or manually inserted by you) passes the namespace, class name and assembly of the page. Armed with this information, the Ajax.PageHandlerFactory is able to use reflection and get the details about any functions which have a certain attribute. Obviously, the handler looks for functions with the AjaxMethod attribute, gets their signature (return type, name, and parameters) and is thus able to create the necessary client-side proxy. Specifically, the wrapper creates a JavaScript object named the same name as your class which exposes the proxy. In other words, given a server-side class AjaxFunctions with an Ajax method ServerSideAdd, we should expect a JavaScript object named AjaxFunction which exposes a ServerSideAdd function. You can see this in action by pointing your browser to the path of the second script tag.

Returning Unicode characters

Ajax .Net wrapper is able to return Unicode characters from the server to the client. To do so, values must be html encoded on the server before being returned. For example:

[Ajax.AjaxMethod] public string Test1(string name, string email, string comment){ string html = ""; html += "Hello " + name + " "; html += "Thank you for your comment "; html += System.Web.HttpUtility.HtmlEncode(comment); html += "."; return html; }

SessionState

It’s likely that you’ll need to access session information in your server side function. To do so, you must simply tell Ajax to enable such functionality via a parameter passed to the Ajax.AjaxMethod attribute.

While looking at the session capabilities of the wrapper, let’s look at a couple other features. In this example, we have a document management system which puts a lock on a document while a user is editing it. Other users can request to be notified when the document because available. Without AJAX, we’d need to wait until the user posted back in order to check if his or her queued documents were available. This is obviously not ideal. Using Ajax with session state support, this is quite easy.

First we’ll write our server side function, the goal of which is to loop through the documentIds the user wishes to edit (stored in a session) and return all released documents.

'Vb.Net HttpSessionStateRequirement.Read)> _ Public Function DocumentReleased() As ArrayList If HttpContext.Current.Session("DocumentsWaiting") Is Nothing Then Return Nothing End If Dim readyDocuments As New ArrayList Dim documents() As Integer = CType(HttpContext.Current.Session("DocumentsWaiting"), Integer()) For i As Integer = 0 To documents.Length - 1 Dim document As Document = document.GetDocumentById(documents(i)) If Not document Is Nothing AndAlso document.Status = DocumentStatus.Ready Then readyDocuments.Add(document) End If Next Return readyDocuments End Function

//C# [Ajax.AjaxMethod(HttpSessionStateRequirement.Read)] public ArrayList DocumentReleased(){ if (HttpContext.Current.Session["DocumentsWaiting"] == null){ return null; } ArrayList readyDocuments = new ArrayList(); int[] documents = (int[])HttpContext.Current.Session["DocumentsWaiting"]; for (int i = 0; i <> Document document = Document.GetDocumentById(documents[i]); if (document != null && document.Status == DocumentStatus.Ready){ readyDocuments.Add(document); } } return readyDocuments; } }

Notice that we specify the HttpSessionStateRequirement.Read value (alternatives being Write and ReadWrite).

Now we write our JavaScript to take advantage of this method:

onload="setTimeout('Document.DocumentReleased(DocumentsReady_CallBack)', 10000);">

Our server side function is called once on page load and subsequently every 10 seconds. The call back function checks the response to see if any values were returned, and if so displays the newly available documents to the user in a div tag.

Conclusion

AJAX technology has already lead to sleek and rich web interfaces, previously reserved for desktop development. The Ajax .Net wrapper allows you to easily take advantage of this new power. Note that both the Ajax .Net wrapper and the documentation are under development.

Keep a close eye on the AJAX .Net wrapper website: http://ajax.schwarz-interactive.de/

For a good hands-on sample, check out the following demo application: http://ajax.schwarz-interactive.de/download/ajaxsample.zip