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AJAX 4使用Visual Basic 2010:服务器端 视频教程 AppDev AJAX 4 Using Visual Basic 2010 Server Side 英文版 DVD

術語Ajax用來描述一組技術,它使瀏覽器可以為用戶提供更為自然的瀏覽體驗。在Ajax之前,Web站點強制用戶進入提交/等待/重新顯示範例,用戶的動作總是與服務器的“思考時間”同步。 Ajax提供與服務器異步通信的能力,從而使用戶從請求/響應的循環中解脫出來。借助於Ajax,可以在用戶單擊按鈕時,使用JavaScript和DHTML立即更新UI,並向服務器發出異步請求,以執行更新或查詢數據庫。當請求返回時,就可以使用JavaScript和CSS來相應地更新UI,而不是刷新整個頁面。最重要的是,用戶甚至不知道瀏覽器正在與服務器通信:Web站點看起來是即時響應的。
雖然Ajax所需的基礎架構已經出現了一段時間,但直到最近異步請求的真正威力才得到利用。能夠擁有一個響應極其靈敏的Web站點確實激動人心,因為它最終允許開發人員和設計人員使用標準的HTML/CSS/JavaScript堆棧創建“桌面風格的(desktop-like)”可用性。
通常,在J2EE中,開發人員過於關注服務和持久性層的開發,以至於用戶界面的可用性已經落後。在一個典型的J2EE開發週期中,常常會聽到這樣的話,“我們沒有可投入UI的時間”或“不能用HTML實現”。但是,以下Web站點證明,這些理由再也站不住腳了:
* BackPack
* Google Suggest
* Google Maps
* PalmSphere
所有這些Web站點都告訴我們,Web應用程序不必完全依賴於從服務器重新載入頁面來向用戶呈現更改。一切似乎就在瞬間發生。簡而言之,在涉及到用戶界面的響應靈敏度時,基准設得更高了。
定義Ajax
Adaptive Path公司的Jesse James Garrett這樣定義Ajax:
  Ajax不是一種技術。實際上,它由幾種蓬勃發展的技術以新的強大方式組合而成。 Ajax包含:
* 基於XHTML和CSS標準的表示;
* 使用Document Object Model進行動態顯示和交互;
* 使用XMLHttpRequest與服務器進行異步通信;
* 使用JavaScript綁定一切。
這非常好,但為什麼要以Ajax命名呢?其實術語Ajax是由Jesse James Garrett創造的,他說它是“Asynchronous JavaScript + XML的簡寫”。
Ajax的工作原理
Ajax的核心是JavaScript對象XmlHttpRequest。該對像在Internet Explorer 5中首次引入,它是一種支持異步請求的技術。簡而言之,XmlHttpRequest使您可以使用JavaScript向服務器提出請求並處理響應,而不阻塞用戶。
在創建Web站點時,在客戶端執行屏幕更新為用戶提供了很大的靈活性。下面是使用Ajax可以完成的功能:
* 動態更新購物車的物品總數,無需用戶單擊Update並等待服務器重新發送整個頁面。
* 提升站點的性能,這是通過減少從服務器下載的數據量而實現的。例如,在Amazon的購物車頁面,當更新籃子中的一項物品的數量時,會重新載入整個頁面,這必須下載32K的數據。如果使用Ajax計算新的總量,服務器只會返回新的總量值,因此所需的帶寬僅為原來的百分之一。
* 消除了每次用戶輸入時的頁面刷新。例如,在Ajax中,如果用戶在分頁列表上單擊Next,則服務器數據只刷新列表而不是整個頁面。
* 直接編輯表格數據,而不是要求用戶導航到新的頁面來編輯數據。對於Ajax,當用戶單擊Edit時,可以將靜態表格刷新為內容可編輯的表格。用戶單擊Done之後,就可以發出一個Ajax請求來更新服務器,並刷新表格,使其包含靜態、只讀的數據。
  一切皆有可能!但願它能夠激發您開始開發自己的基於Ajax的站點。然而,在開始之前,讓我們介紹一個現有的Web站點,它遵循傳統的提交/等待/重新顯示的範例,我們還將討論Ajax如何提升用戶體驗。
AJAX is based on a collection of open and standards-based technologies that can give Web pages you build a responsiveness that rivals what you get in desktop applications. The course starts out with an exploration of the fundamentals of AJAX. Then you'll go through a few of the more interesting features in JavaScript that will help you write code that runs in the browser. Next up is an introduction to the five server-side controls that you can use in a Web forms page to reduce the amount of data that has to move between client and server. Then you'll explore some of the techniques you can use to create applications that give users a good experience with your Web application. Next you'll look at the AJAX Control Toolkit, a collection of server-side controls and extenders that do a lot of the work that you used to have to write reams of JavaScript code to accomplish.
In this course, you will learn:
* A few of the more interesting features in JavaScript that will help you write code that runs in the browser
* About the server and client-side components of ASP.NET AJAX
* About avoiding full page postbacks that flash in the browser and can be intolerably slow for a user
* With your Web application how to use multiple UpdatePanel controls
* With your Web application hooking into the browser's history feature
Prerequisites: This course assumes that you are familiar and experienced with Microsoft's .NET Framework and ASP.NET development tools. You should be familiar with Web development and understand how HTTP and HTML work to produce Web pages for the user. You should have experience writing applications with ASP.NET 3.5, 4.0, or later Web forms, and be familiar with how ASP.NET processes page requests, and have strong experience with .NET Framework 3.5, 4.0, or later programming. You should have experience with Visual Studio 2008 , 2010, or later for building Web application projects. Experience with building database applications using these tools will be helpful, although not strictly necessary. You should also have some experience with writing JavaScript.
Your Instructor
Don Kiely has been using and programming computers since the mid-1970s, when he first punched IBM punch cards for batch processing to solve engineering problems. Now Don is a nationally recognized author, instructor and consultant who travels the country sharing his expertise in SQL Server and security. He has written business software using assembly, C/C++, dBASE, Nantucket Clipper, RPG II, C#, and Visual Basic for a variety of industries, and has taught software and business administration courses at community colleges. Now Don is an author and presenter for AppDev, and a consultant for a variety of companies that develop distributed applications for public and private organizations. Don is also the author or coauthor of several programming books, and a featured speaker at SQL Server conferences.
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