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AJAX Toolkit in Microsoft Visual Studio - PART1

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أستاذ المادة حۡــسۜــنۨ ا̍ڷــڔهــٻۧــمۘــې       25/02/2014 19:18:29
perhaps the most visible feature of the asp.net ajax extensions is the ability to do a partial or incremental page updatings without doing a full postback to the server, with no code changes and minimal markup changes. the advantages are extensive – the state of your multimedia (such as adobe flash or windows media) is unchanged, bandwidth costs are reduced, and the client does not experience the flicker usually associated with a postback.


introduction

microsoft s asp.net technology brings an object-oriented and event-driven programming model and unites it with the benefits of compiled code. however, its server-side processing model has several drawbacks inherent in the technology:

1)page updatings require a round-trip to the server, which requires a page refresh.
2)round-trips do not persist any effects generated by javascript or other client-side technology (such as adobe flash)
3)during postback, browsers other than microsoft internet explorer do not support automatically restoring the scroll position. and even in internet explorer, there is still a flicker as the page is refreshed.
4)postbacks may involve a high amount of bandwidth as the __viewstate form field may grow, especially when dealing with controls such as the gridview control or repeaters.
5)there is no unified model for accessing web services through javascript or other client-side technology.


enter microsoft s asp.net ajax extensions. ajax, which stands for asynchronous javascript and xml, is an integrated framework for providing incremental page updatings via cross-platform javascript, composed of server-side code comprising the microsoft ajax framework , and a script component called the microsoft ajax script library. the asp.net ajax extensions also provide cross-platform support for accessing asp.net web services via javascript.



partial page updatings

perhaps the most visible feature of the asp.net ajax extensions is the ability to do a partial or incremental page updatings without doing a full postback to the server, with no code changes and minimal markup changes. the advantages are extensive - the state of your multimedia (such as adobe flash or windows media) is unchanged, bandwidth costs are reduced, and the client does not experience the flicker usually associated with a postback.
scriptmanager
any ajax control requires the existence of scriptmanager to run ajaxified forms . the scriptmanager control is the essential core for the asp.net ajax extensions. it provides access to the script library (including the extensive client-side script type system), supports partial rendering, and provides extensive support for additional asp.net services (such as authentication and profiling, but also other web services). the scriptmanager control also provides globalization and localization support for the client scripts.



ajax updatingpanel triggers
when working in the markup editor in visual studio, you may notice (from intellisense) that there are two child elements of an updatingpanel control. one of which is the triggers element, which specifies the controls on the page (or the user control, if you are using one) that will trigger a partial render of the updatingpanel control in which the element resides.



triggers for a given updatingpanel, by default, automatically include any child controls that invoke a postback, including (for example) textbox controls that have their autopostback property set to true. however, triggers can also be included declaratively using markup this is done within the section of the updatingpanel control declaration. although triggers can be accessed via the triggers collection property, it is recommended that you register any partial render triggers at run-time (for instance, if a control is not available at design time) by using the registerasyncpostbackcontrol(control) method of the scriptmanager object for your page, within the page_load event. remember that pages are stateless, and so you should re-register these controls every time they are created.

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