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Dynamic HTML (DHTML) combines 3 technologies: Cascading Style Sheets (CSS) refines HTML formatting and provides better control over positioning and layering.

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Presentation on theme: "Dynamic HTML (DHTML) combines 3 technologies: Cascading Style Sheets (CSS) refines HTML formatting and provides better control over positioning and layering."— Presentation transcript:


2 Dynamic HTML (DHTML) combines 3 technologies: Cascading Style Sheets (CSS) refines HTML formatting and provides better control over positioning and layering content JavaScript (not Java), a scripting language for web browsers SCRIPT tag in HTML indicates language: Document Object Model (DOM) exposes all the attributes of HTML and Style Sheets to JavaScript control DOM lets JavaScript programmers view and modify the properties of web pages, dynamically.

3 Cascading Style Sheets (CSS) World Wide Web Consortium (W3C), 1996 First supported in Netscape 4 and IE 4 Style sheets are groups of rules, defining how an HTML element appears in a browser Following sets color of all FONT tags to blue: FONT { color : blue; } Every HTML tag that fit a sector’s specifications gets its declarations: Cookie Monster FONT is known as the sector and color : blue {within braces} is a declaration

4 Classes control scope It can get a little tricky to distinguish between all the FONT tags you might want to declare Following snippet uses dot notation to define a class BIGBIRD within as a subclass of H3: H3.BIGBIRD { color : yellow; } /* CLASS */ Big Bird See cssFormatting.htmcssFormatting.htm

5 Declaring a font-family A font-family declaration specifies a specific font you want to use in your site:.COOKIEM { font-family:"Sesame Street", "Kidprint", sans-serif; /* Try these fonts, in order */ font-size: 24pt; font-weight: bold; text-transform: uppercase; } Cookie Monster

6 Site basis integration Lets you create a.css file, then load it into each page in your site: Put your style sheet (like the code above) in a file, e.g., mystylesheet.css Put the following code in the HEAD of all your HTML pages:

7 Background images Declarations for a background image of a page: background-image: url(yourbackground.gif) || none; background-repeat: repeat-x || repeat-y || repeat; background-attachment: fixed || scroll; background-image: sets a background image from file background-repeat: repeat X-ward (right) or Y (down) background-attachment: background scrolls with text?.COOLBACK { background-color: blue; background-image: url(greenbox.jpg); font-size: 14pt; font-weight: bold; } Look at how cool this text is!

8 CSS level 2 positioning Introduces positioning, providing direct of control over Web page layout How do HTML developers typically arrange objects on a page? Tables to arrange objects can be awkward Instead you can place each object exactly: H1 { position:absolute; top:150px; left:300px; width:200px; height:200px } Places text at absolute coordinates (pixels from top left corner) and size (width and height)

9 Inline styles,, Of course, you probably don't want all your elements to appear in the same spot Instead, this code positions only the contents of a particular element: A red 200-by-200-pixel box, 300 pixels from top and 100 from left edges of window. See cssPositioning.htmcssPositioning.htm

10 Relative positioning Relative positioning places elements into flow of the document--offsetting them from previous element in the HTML code: This text will flow normally across the page, while the next line of text will be offset from the end of this line. This text is offset from the above line--50 pixels on top and 25 pixels on the left.

11 Z-layering of objects Layering lets object overlap each other In addition to x- and y-coodinates, add z-index:.over { position:absolute; top:500px; left:50px; z-index:2; background-color:green }.under { position:absolute; top:510px; left:50px; z-index:1; background-color:blue } This text is positioned 20 pixels from the left and 165 pixels from the top of the window. This text is positioned just below the above text, and would usually be placed on top because of its order on the page.

12 Analyzing a document Simple DOM Demo This is the document body This is paragraph 1. Paragraph 2 From the root you can go to one of its four children Reach first child using bodyNode.firstChild or bodyNode.childNodes[0] Access third (and last) child by bodyNode.childNodes[2] or bodyNode.lastChild Or use tags with a unique ID : p1Node.nextSibling accesses p2Node

13 Dynamic HTML Supports animations & rollover effects No plug-ins: it’s part of HTML 4.0 Different browsers provide different support for HTML 4.0 JavaScript programs dynamic behaviors JavaScript JavaScript functions manipulate DOM objects Dreamweaver provides high level interface generating JavaScript code for a few common dynamic behaviors

14 Rollover effect in DHTML Preview in comingDone.htmlcomingDone.html Effect achieved by swapping images from files into memory In Dreamweaver, open coming.htm:coming.htm choose Insert > Image & select redlite.gif In Property Inspector, enter: “redlight” Set Border to 0 (no border around image) Select image, then windows > Behaviors Hold down + button and select the Swap image Select grnlite.gif as swap image Leave Preload Images and Restore Images onMouseOut on Why is pre-storing in array crucial to rollover effect? Dreamweaver makes it even easier: Insert>Image Objects>Rollover Image

15 Rollover effect in Javascript Look at source code view in DW function MM_preloadImages(): sets local variable d to document: why? creates new Array called d.MM_p MM_preloadImages.arguments reads onLoad="MM_preloadImages('grnlite.gif')" function MM_swapImage(): stores MM_swapImage.arguments findObj locates the other image

16 More DHTML examples Jeff Lutz’s example (note animated butterfly) Jeff Lutz’s example Dreamweaver generates timeline functions Timeline interface similar to Flash Drag-and-drop map puzzle

17 What is AJAX? See an examplean example Asynchronous JAvaScript And XML Developed by Adaptive Path Combines several established technologies: Standards based display CSS – Cascading style sheets XHTML – Extensible Hyper Text Markup Language Dynamic display manipulation with DOM Data interchange and manipulation with XML Asynchronous data retrieval with XMLHttpRequest JavaScript functions to bind everything together

18 XMLHttpRequest Can transfer and manipulate XML data between a client and server Originally an ActiveX object developed by Microsoft accessible by scripting languages, such as VBScript Mozilla 1.0 included a compatible native version, XMLHttpRequest

19 Classic Web Application Model Disadvantages? What is the user doing? WAITING Application does not allow user interaction while the information is being processed While user interacting with the browser, the server is not processing information for that user

20 Classic Web Application Model (Synchronous)

21 The AJAX Engine Intermediary layer between user and server Instead of just loading a webpage, browser loads the AJAX Engine Written in JavaScript Usually located in a hidden frame Responsible for displaying the user interface and communicating with the server Allows the user to interact asynchronously – independent of communication with the server Communicates with the server, usually with XML

22 AJAX Web Application Model (Asynchronous)

23 AJAX Web Application Model Advantages? Application is more responsive Any action that does not require the information from the server is handled by the engine User interaction and data processing can occur concurrently Disadvantages? Added technical complexity Potential security issues

24 Is AJAX better than Flash? Yahoo Maps Google Maps What do you think?

25 AJAX advantages vs. Flash Searchablitity: text pages are more visible to search engines than Flash Open source vs. Flash licensing AJAX does not require plug-ins However, users must have JavaScript enabled Cost: Adobe has driven up cost of Flash development Accessibility Font and color settings in AJAX default to those of the environment Flash applications use developer specified settings which may be more difficult for disabled users Screen readers or acceleration keys may not be available in Flash Security--Flash sites may not be as trusted as an HTML site Can be used to avoid pop-up blockers Can be used to create immortal cookies

26 Flash pros vs. AJAX Media Handling? Better handling of sound and graphics Vector Graphics May take up less space than bitmaps and are easily scalable While available in most web browsers, either native or as a plug-in, vector graphics are more commonly used in Flash Compatibility No discrepancy between browsers (just one distributor) Machine Access Flash apps have better access to resources of user’s computer

27 AJAX versus Flash So which is better? Both have certain strengths Two solutions: Analyze needs and choose accordingly Make Flash and AJAX can work together: yFeedReport/ yFeedReport/

28 How to Code “By hand” Use a framework prototype ( (add-on to prototype.js, cross-browser user interface JS libraries

29 Wrap up Asynchronous JavaScript And XML Combines several existing technologies Can create rich and dynamic web pages Improves responsiveness of web based applications

30 AJAX References chives/000385.php chives/000385.php s/KN-Beyond-AJAX.pdf s/KN-Beyond-AJAX.pdf 06/01/flash_and_AJAX_1.cfm 06/01/flash_and_AJAX_1.cfm AX_o.html AX_o.html ent/0,289142,sid26_gci1150930,00.html ent/0,289142,sid26_gci1150930,00.html

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