| AJAX With .NET Framework |
| ASP.NET AJAX is a free framework for quickly creating efficient and interactive Web applications that work across all popular browsers. The following Contents in this section provide guidance on how to improve of your application through using of .Net Framework with AJAX. |
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| Ajax programming overview |
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| Ajax (Asynchronous JavaScript and XML), is a group of inter-related web development techniques used for creating interactive web applications. A primary characteristic is the increased responsiveness and interactivity of web pages achieved by exchanging small amounts of data with the server "behind the scenes" so that entire web pages do not have to be reloaded each time there is a need to fetch data from the server. This is intended to increase the web page's interactivity, speed, functionality and usability. |
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| Ajax is asynchronous, in that extra data is requested from the server and loaded in the background without interfering with the display and behavior of the existing page. JavaScript is the scripting language in which Ajax function calls are usually made.[1] Data is retrieved using the XMLHttpRequest object that is available to scripting languages run in modern browsers, or, alternatively, through the use of Remote Scripting in browsers that do not support XMLHttpRequest. In any case, it is not required that the asynchronous content be formatted in XML. |
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| Ajax is a cross-platform technique usable on many different operating systems, computer architectures, and web browsers as it is based on open standards such as JavaScript and the DOM. There are free and open source implementations of suitable frameworks and libraries. |
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| Constituent technologies |
| Ajax uses a combination of: |
| XHTML (or HTML) and CSS for marking up and styling information. |
| The DOM accessed with a client-side scripting language, especially ECMAScript implementations such as JavaScript and JScript, to dynamically display and interact with the information presented. |
| The XMLHttpRequest object is used to exchange data asynchronously with the web server. In some Ajax frameworks and in certain situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server, and in other implementations, dynamically added tags may be used. |
| XML is sometimes used as the format for transferring data between the server and client, although any format will work, including preformatted HTML, plain text and JSON. These files may be created dynamically by some form of server-side scripting. |
| Like DHTML and LAMP, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies. |
| The "core" and defining element of Ajax is the XMLHttpRequest object, which gives browsers the ability to make dynamic and asynchronous data requests without having to reload a page, eliminating the need for page refreshes. |
| Besides XMLHttpRequest, the use of DOM, CSS and JavaScript provides a richer "single-page" experience. |
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| History |
| Techniques for the asynchronous loading of content on an existing Web page without requiring a full reload date back as far as the src attribute that could take any external URL, and by loading a page containing JavaScript that manipulated the parent page, Ajax-like effects could be attained. This set of client-side technologies was usually grouped together under the generic term of DHTML. Macromedia's Flash could also, from version 4, load XML and CSV files from a remote server without requiring a browser to be refreshed. |
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| Microsoft's Remote Scripting (MSRS), introduced in 1998, acted as a more elegant replacement for these techniques, with data being pulled in by a Java applet with which the client side could communicate using JavaScript. This technique worked on both Internet Explorer version 4 and Netscape Navigator version 4 onwards. Microsoft then created the XMLHttpRequest object in Internet Explorer version 5 and first took advantage of these techniques using XMLHttpRequest in Outlook Web Access supplied with the Microsoft Exchange Server 2000 release. |
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| The Web development community, first collaborating for remote scripting to enable consistent results across different browsers. In 2002 a user-community modification to Microsoft Remote Scripting was made to replace the Java applet with XMLHttpRequest. |
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| Remote Scripting Frameworks such as ARSCIF surfaced in 2003 not long before Microsoft introduced Callbacks in ASP.NET. |
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| In addition, the World Wide Web (W3C) Consortium has several recommendations that also allow for dynamic communication between a server and user agent, though few of them are well supported. These would include: |
| The object element defined in HTML 4 for embedding arbitrary content types into documents (replaces inline frames under XHTML 1.1). |
| The Document Object Model (DOM) Level 3 Load and Save Specification |
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| Justification |
| The core justification for Ajax-style programming is to overcome the page loading requirements of HTML/HTTP-mediated web pages. Ajax creates the necessary initial conditions for the evolution of complex, intuitive, dynamic, data-centric user interfaces in web pages. Indeed, much of the Web's innovation and evolution during the Web 2.0 era has relied upon and benefited immensely from the capabilities of an Ajax platform. |
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| Web pages, unlike native applications, are loosely coupled, meaning that the data they display are not tightly bound to data sources and must be first marshaled (set out in proper order) into an HTML page format before they can be presented to a user agent on the client machine. For this reason, web pages have to be re-loaded each time a user needs to view different datasets. By using the XMLHttpRequest object to request and return data without a re-load, a programmer bypasses this requirement and makes the loosely coupled web page behave much like a tightly coupled application, but with a more variable lag time for the data to pass through a longer "wire" to the remote web browser. |
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| For example, in a classic desktop application, a programmer has the choice of populating a tree view control with all the data needed when the form initially loads, or with just the top-most level of data-which would load more quickly, especially when the dataset is very large. In the second case, the application would fetch additional data into the tree control depending on which item the user selects. This functionality is difficult to achieve in a web page without Ajax. To update the tree based on a user's selection would require the entire page to re-load, leading to a very jerky, non-intuitive feel for the web user who is browsing the data in the tree. |
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| Advantages of Ajax |
| Bandwidth usage |
| By generating the HTML locally within the browser, and only bringing down JavaScript calls and the actual data, Ajax web pages can appear to load relatively quickly since the payload coming down is much smaller in size, and the rest of the layout does not have to be redrawn on each update. An example of this technique is a large result set where multiple pages of data exist. With Ajax, the HTML of the page (e.g., a table structure with related <TR> and <TD> tags) can be produced locally in the browser, not brought down with the first page of the document. In addition to "load on demand" of contents, some web-based applications load stubs of event handlers and then load the functions on the fly. This technique significantly cuts down the bandwidth consumption for web applications. In addition Ajax works on the client and shares some work of the server, reducing the server load. |
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| Separation of data, format, style, and function |
| A less specific benefit of the Ajax approach is that it tends to encourage programmers to clearly separate the methods and formats used for the different aspects of information delivery via the web. Although Ajax can appear to be a jumble of languages and techniques, and programmers are free to adopt and adapt whatever works for them, they are generally propelled by the development motive itself to adopt separation among the following: |
| 1. Raw data or content to be delivered, which is normally embedded in XML and sometimes derived from a server-side database. |
| 2. Format or structure of the webpage, which is almost always built in HTML or XHTML and is then reflected and made available to dynamic manipulation in the DOM. |
| 3. Style elements of the webpage: everything from fonts to picture placement are derived by reference to embedded or referenced CSS. |
| 4. Functionality of the webpage, which is provided by a combination of: |
| 1. Javascript on the client browser (Also called DHTML), |
| 2. Standard HTTP and XMLHttp or client-to-server communication, and |
| 3. Server-side scripting and/or programs using any suitable language preferred by the programmer to receive the client's specific requests and respond appropriately. |
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| ASP.NET AJAX |
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| AJAX features in ASP.NET enable you to quickly create Web pages that include a rich user experience with responsive and familiar user interface (UI) elements. AJAX features include client-script libraries that incorporate cross-browser ECMAScript (JavaScript) and dynamic HTML (DHTML) technologies, and integration with the ASP.NET server-based development platform. By using AJAX features, you can improve the user experience and the efficiency of your Web applications. |
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Why Use ASP.NET AJAX Features? |
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| AJAX features in ASP.NET enable you to build rich Web applications that have many advantages over Web applications that are completely server-based. AJAX-enabled applications offer: |
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| Improved efficiency, because significant parts of a Web page's processing are performed in the browser. |
| Familiar UI elements such as progress indicators, tooltips, and pop-up windows. |
| Partial-page updates that refresh only the parts of the Web page that have changed. |
| Client integration with ASP.NET application services for forms authentication, roles, and user profiles. |
| Auto-generated proxy classes that simplify calling Web service methods from client script. |
| A framework that lets you customize of server controls to include client capabilities. |
| Support for the most popular and generally used browsers, which includes Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari. |
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Architecture of AJAX Features in ASP.NET |
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| The architecture of AJAX features in ASP.NET consists of two pieces: client-script libraries and server components. These pieces are integrated to provide a robust development framework. |
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Note: |
| In addition to the AJAX features in ASP.NET, you can use the ASP.NET AJAX Control Toolkit and the features in the Microsoft ASP.NET Futures releases, which are both community supported. |
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| The following illustration shows the functionality that is included in the client-script libraries and server components. |
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| ASP.NET AJAX client and server architecture |
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| The illustration shows the functionality of the client-based Microsoft AJAX Library, which includes support for creating client components, browser compatibility, and networking and core services. The illustration also shows the functionality of server-based AJAX features, which include script support, Web services, application services, and server controls. The following sections describe the illustration in more detail. |
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AJAX Client Architecture |
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| The client architecture includes libraries for component support, browser compatibility, networking, and core services. |
| Components |
| Client components enable rich behaviors in the browser without postbacks. Components fall into three categories: |
| Components, which are non-visual objects that encapsulate code, such as a timer object. |
| Behaviors, which extend the basic behavior of existing DOM elements. |
| Controls, which represent a new DOM element that has custom behavior. |
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| The type of component that you use depends on the type of client behavior you want. For example, a watermark for an existing text box can be created by using a behavior that is attached to the text box. |
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| Browser Compatibility |
| The browser compatibility layer provides AJAX scripting compatibility for the most frequently used browsers (including Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari). This enables you to write the same script regardless of which supported browser you are targeting. |
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| Networking |
| The networking layer handles communication between script in the browser and Web-based services and applications. It also manages asynchronous remote method calls. In many common scenarios, such as partial-page updates that use the UpdatePanel control, the networking layer is used automatically and does not require that you write any code. |
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| The networking layer also provides support for accessing server-based forms authentication, role information, and profile information in client script. This support is also available to Web applications that are not created by using ASP.NET, as long as the application has access to the Microsoft AJAX Library. |
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| Core Services |
| The AJAX client-script libraries in ASP.NET consist of JavaScript (.js) files that provide features for object-oriented development. The object-oriented features included in the ASP.NET AJAX client-script libraries enable a high level of consistency and modularity in client scripting. The following core services are part of the client architecture: |
| Object-oriented extensions to JavaScript, such as classes, namespaces, event handling, inheritance, data types, and object serialization. |
| A base class library, which includes components such as string builders and extended error handling. |
| Support for JavaScript libraries that are either embedded in an assembly or are provided as standalone JavaScript (.js) files. Embedding JavaScript libraries in an assembly can make it easier to deploy applications and can help solve versioning issues. |
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| Debugging and Error Handling |
| The core services include the Sys.Debug class, which provides methods for displaying objects in readable form at the end of a Web page. The class also shows trace messages, enables you to use assertions, and lets you break into the debugger. An extended Error object API provides helpful exception details with support for release and debug modes. |
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| Globalization |
| The AJAX server and client architecture in ASP.NET provides a model for localizing and globalizing client script. This enables you to design applications that use a single code base to provide UI for many locales (languages and cultures). For example, the AJAX architecture enables JavaScript code to format Date or Number objects automatically according to culture settings of the user's browser, without requiring a postback to the server. |
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AJAX Server Architecture |
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| The server pieces that support AJAX development consist of ASP.NET Web server controls and components that manage the UI and flow of an application. The server pieces also manage serialization, validation, control extensibility, and so on. There are also ASP.NET Web services that enable you to access ASP.NET application services for forms authentication, roles, and user profiles. |
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| Script Support |
| AJAX features in ASP.NET are implemented by using supporting scripts that are sent from the server to the client. Depending on what AJAX features that you enable, different scripts are sent to the browser. |
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| You can also create custom client script for your ASP.NET applications. In that case, you can also use AJAX features to manage your custom script as static .js files (on disk) or as .js files embedded as resources in an assembly. |
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| ASP.NET AJAX features include a model for release and debug modes. Release mode provides error checking and exception handling that is optimized for performance, with minimized script size. Debug mode provides more robust debugging features, such as type and argument checking. ASP.NET runs the debug versions when the application is in debug mode. This enables you to throw exceptions in debug scripts while minimizing the size of release code. |
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| Script support for AJAX in ASP.NET is used to provide two important features: |
| The Microsoft AJAX Library, which is a type system and a set of JavaScript extensions that provide namespaces, inheritance, interfaces, enumerations, reflection, and additional features. |
| Partial-page rendering, which updates regions of the page by using an asynchronous postback. |
| Localization |
| The ASP.NET AJAX architecture builds on the foundation of the ASP.NET 2.0 localization model. It provides additional support for localized .js files that are embedded in an assembly or that are provided on disk. ASP.NET can serve localized client scripts and resources automatically for specific languages and regions. |
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| Web Services |
| With AJAX functionality in an ASP.NET Web page, you can use client script to call both ASP.NET Web services (.asmx) and Windows Communication Foundation (WCF) services (.svc). The required script references are automatically added to the page, and they in turn automatically generate the Web service proxy classes that you use from client script to call the Web service. |
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| You can also access ASP.NET Web services without using ASP.NET AJAX server controls (for example, if you are using a different Web development environment). To do so, in the page you can manually include references to the Microsoft AJAX Library, to script files, and to the Web service itself. At run time, ASP.NET generates the proxy classes that you can use to call the services. |
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| Application Services |
| Application services in ASP.NET are built-in Web services that are based on ASP.NET forms authentication, roles, and user profiles. These services can be called by client script in an AJAX-enabled Web page, by a Windows client application, or by a WCF-compatible client. |
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| Server Controls |
| ASP.NET AJAX server controls consist of server and client code that integrate to produce rich client behavior. When you add an AJAX control to an ASP.NET Web page, the page automatically sends supporting client script to the browser for AJAX functionality. You can provide additional client code to customize the functionality of a control, but this is not required. |
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| The following list describes the most frequently used ASP.NET AJAX server controls. |
| ScriptManager |
| Manages script resources for client components, partial-page rendering, localization, globalization, and custom user scripts. The ScriptManager control is required in order to use the UpdatePanel, UpdateProgress, and Timer controls. |
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| UpdatePanel |
| Enables you to refresh selected parts of the page, instead of refreshing the whole page by using a synchronous postback. |
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| UpdateProgress |
| Provides status information about partial-page updates in UpdatePanel controls. |
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| Timer |
| Performs postbacks at defined intervals. You can use the Timer control to post the whole page, or use it together with the UpdatePanel control to perform partial-page updates at a defined interval. |
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| You can also create custom ASP.NET server controls that include AJAX client behaviors. Custom controls that enhance the capabilities of other ASP.NET Web controls are referred to as extender controls. |
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AJAX Control Toolkit |
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| The ASP.NET AJAX Control Toolkit is a collection of samples and components that show you some of the experiences you can create with ASP.NET AJAX controls and extenders. The Control Toolkit provides samples and a powerful SDK to make it simple to create and reuse custom controls and extenders. You can download the ASP.NET AJAX Control Toolkit from the ASP.NET Ajax Web site. The ASP.NET AJAX Control Toolkit is community supported. |
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AJAX Community-supported Futures Releases |
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| The ASP.NET AJAX community-supported Futures releases provide features that extend the AJAX capabilities of ASP.NET with functionality that remains under development and that is not included in ASP.NET. This includes additional extender controls, support for client declarative syntax (xml-script), and more. |
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| Using Web Services in ASP.NET AJAX |
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| This topic describes how to access Web services from client script in AJAX-enabled ASP.NET Web pages. The services can be either custom services that you create, or built-in application services. The application services are provided as part of ASP.NET AJAX, and include authentication, roles, and profile services. |
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| Custom Web services can be in the form of .ASP.NET Web services (.asmx services), or Windows Communication Foundation (WCF) services (.svc services). |
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| This topic contains the following information: |
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Scenarios |
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| You use WCF and ASP.NET in the following cases: |
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| If you have already created WCF services, you can add endpoints to enable script in AJAX-enabled Web pages to access the services. |
| If you have already created ASP.NET Web (.asmx) services, you can modify them to enable script in AJAX-enabled Web pages to access the same service. |
| If you want to create a custom Web service that will be accessed from ASP.NET AJAX Web pages, you can implement it as a WCF service or as an ASP.NET Web service (.asmx file). |
| You can use the built-in ASP.NET application services to access users' authentication, roles, and profile information from client script that runs in an AJAX-enabled Web page. |
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| Background |
| ASP.NET enables you to create Web services can be accessed from client script in Web pages. The pages communicate with the server through a Web service communication layer that uses AJAX technology to make Web service calls. Data is exchanged asynchronously between client and server, typically in JSON format. |
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| Client-Server Communication for AJAX Clients |
| In AJAX-enabled Web pages, the browser makes an initial request to the server for the page, and then makes subsequent asynchronous requests to Web services for data. The client communication elements are in the form of downloaded proxy classes from the server and the core client-script library. The server communication elements are handlers and custom services. The following illustration shows the elements that are involved in the communication between the client and the server. |
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| Client Server Communication |
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| AJAX Client Architecture |
| Browsers call Web service methods by using proxy classes. A proxy class is a script that is automatically generated by the server and downloaded to the browser at page-load time. The proxy class provides a client object that represents the exposed methods of a Web service. |
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| To call a Web service method, client script calls the corresponding methods of the proxy class. The calls are made asynchronously, through the XMLHTTP object. |
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| The Web service communication layer contains the library script types that enable the proxy classes to make service calls |
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| The code in the proxy classes and in the core Web service communication layer hides the complexity of XMLHTTP and the differences between browsers. This simplifies the client script that is required to call the Web service. |
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| There are two approaches to making a Web service request: |
| Call Web services by using the HTTP POST verb. A POST request has a body that contains the data that the browser sends to the server. It does not have a size limitation. Therefore, you can use a POST request when the size of the data exceeds the intrinsic size limitation for a GET request. The client serializes the request into JSON format and sends it as POST data to the server. The server deserializes the JSON data into .NET Framework types and makes the actual Web service call. During the response, the server serializes the return values and passes them back to the client, which deserializes them into JavaScript objects for processing. |
| Call Web services by using the HTTP GET verb. This resembles the functionality of a POST request, with the following differences: |
| The client uses a query string to send the parameters to the server. |
| A GET request can call only a Web service method that is configured by using the ScriptMethodAttribute attribute. |
| Data size is limited to the URL length allowed by the browser. |
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Note: |
| In addition to the AJAX features in ASP.NET, you can use the ASP.NET AJAX Control Toolkit and the features in the Microsoft ASP.NET Futures releases, which are both community supported. |
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| The following illustration shows the ASP.NET AJAX client architecture. |
| AJAX Client Architecture |
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| Elements of the client architecture include the Web service communication layer in the core library and the downloaded proxy classes for the services that are used on the page. Individual elements shown in the figure are as follows: |
| Custom Service Proxy Classes. These consist of client script that is automatically generated by the server and downloaded to the browser. The proxy classes provide an object for each WCF or ASMX service that is used in the page. (That is, they provide an object for each item in the ServiceReferences element of the ScriptManager control in the page.) Calling a proxy method in client script creates an asynchronous request to the corresponding Web service method on the server. |
| Authentication Proxy Class. The AuthenticationService proxy class is generated by the server authentication application service. It enables the user to log on or log out through JavaScript in the browser without making a round trip to the server. |
| Role Proxy Class. The RoleService proxy class is generated by the server roles application service. It enables you to group users and treat each group as a unit through JavaScript without making round trips to the server. This can be useful to enable or deny access to resources on the server. |
| Profile Proxy Class. The ProfileService class is generated by the server profile application service. It makes the current user's profile information available to the client through JavaScript without making round trips to the server. |
| Page Methods Proxy Class. This provides the scripting infrastructure for client script to call static methods in an ASP.NET page as if they were Web service methods. |
| Web Service Communication Layer. This is the library that contains the client script types. These types enable the browser (client) to communicate with the services on the server. They also shield client applications from the complexities of establishing and maintaining the asynchronous communication between client and server. They encapsulate the browser XMLHTTP object that provides the asynchronous capability, and enable client applications to be browser independent. The following are the main elements of the Web service communication layer: |
| WebRequest. This provides client script functionality to make a Web request. For more information, see the WebRequest class. |
| WebRequestManager. This manages the flow of the Web requests issued by the WebRequest object to the associated executor object. For more information, see the WebRequestManager class. |
| XmlHttpExecutor. This makes asynchronous network requests by using the browser's XMLHTTP support. For more information, see the XmlHttpExecutor class. |
| JSON Serialization. This serializes JavaScript objects into JSON format. Deserialization is available by using the JavaScript eval function. |
| The default serialization format is JSON, but individual methods in Web services and in ASP.NET Web pages can return alternative formats such as XML. The serialization format of a method can be specified with attributes. For example, for an ASMX service, you can set the ScriptMethodAttribute attribute to cause a Web service method to return XML data, as shown in the following example: |
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<authorization>
<[allow|deny] users roles verbs />
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| AJAX Server Architecture |
| The following illustration shows the AJAX server architecture, which includes the elements that enable communication with client applications. |
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| AJAX Server Architecture |
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| Elements of the server architecture include the Web service communication layer with a HTTP handler and serialization classes, custom services, page methods, and application services. Individual elements shown in the figure are as follows: |
| Custom Web Services. These provide the service functionality that you implement and return the appropriate response to the client. Custom Web services can be ASP.NET or WCF services. The Web service communication layer automatically generates client-script proxy classes that can be called asynchronously from client script. |
| Page Methods. This component enables a method in an ASP.NET page to be called as if it were a Web service method. Page methods must be defined in the page that is performing the page-method call. |
| Authentication Service. The authentication service generates an authentication proxy class that enables the user to log on or log out through client JavaScript. This application service is always available and you do not have to instantiate it. |
| Role Service. The role service generates a role proxy class that enables client JavaScript to access roles information for the currently authenticated user. This application service is always available and you do not have to instantiate it. |
| Profile Service. The profile service generates a profile proxy class that enables client JavaScript to get and set profile properties for the user that is associated with the current request. This application service is always available and you do not have to instantiate it. |
| JSON Serialization. The server JSON serialization component enables customizable serialization and deserialization of common .NET Framework types to and from JSON format. |
| XML Serialization. The Web service communication layer supports XML serialization for SOAP requests to Web services and for returning XML types from a JSON request to a Web service. |
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| Security Settings for AJAX Enabled ASP.NET Pages |
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| AJAX functionality in ASP.NET is compatible with most modern browsers. It runs with the default security settings for these browsers. |
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Browser and Operating System Compatibility |
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| Users can view your AJAX-enabled ASP.NET sites by using most modern browsers. The following lists show compatible browser versions and operating systems. |
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| Supported Browsers |
| Microsoft Internet Explorer 6.0 or later versions. |
| Mozilla Firefox version 1.5 or later versions. |
| Opera version 9.0 or later versions. |
| Apple Safari version 2.0 or later versions. |
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| Supported Operating Systems |
| Microsoft Windows XP with Service Pack 2 installed. |
| Microsoft Vista. |
| Apple OSX (Intel architecture only). |
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Security and Privacy Settings |
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| The following table lists required browser security and privacy settings for both user browsing and site development. In all cases, the recommended settings are the default settings for that browser. |
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| Internet Explorer 6 |
Make sure that the Internet Zone in the Security Zones settings is set to Medium. |
| Internet Explorer 7 |
Make sure that the Internet Zone in the Security Zones settings is set to Medium-High. |
| FireFox 1.5 or later versions |
In the Tools menu under Options, make sure that Enable JavaScript is selected. |
| Opera 9.0 or later versions |
In the Tools menu under Quick preferences, make sure that Enable JavaScript is selected. |
| Safari 2.0.4 or later versions |
Click Safari, Preferences, Security, and then Web Content and make sure that Enable JavaScript is selected. |
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Note: |
| In addition to the AJAX features in ASP.NET, you can use the ASP.NET AJAX Control Toolkit and the features in the Microsoft ASP.NET Futures releases, which are both community supported. |
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