1 / 8

Access to Event Object

This guide covers how to implement draggable elements in an HTML document using JavaScript. By utilizing event handling methods for mouse events (mousedown, mousemove, mouseup), we create a draggable rectangle feature. The provided code showcases how to track mouse movements and update an element's position dynamically while dragging. It explains the role of global and event-specific variables in different browsers, providing a comprehensive understanding for students in CS 142. Learn the intricacies of event handling and object manipulation in the DOM.

deron
Télécharger la présentation

Access to Event Object

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Access to Event Object • event variable (HTML): <div onclick="mouseClick(event);"> • Passed as argument to function (DOM/Firefox): element.onclick = mouseClick; function mouseClick(evt) { ... x = evt.clientX; ... } • Global variable (DOM/IE): element.onclick = mouseClick; function mouseClick() { ... x = window.event.clientX; ... } CS 142 Lecture Notes: Events

  2. Draggable Rectangle <style type="text/css"> #div1 { position: absolute; } </style> ... <div id="div1" onmousedown="mouseDown(event);" onmousemove="mouseMove(event);" onmouseup="mouseUp(event);">Drag Me!</div> CS 142 Lecture Notes: Events

  3. Dragging Application isMouseDown = false; function mouseDown(event) { prevX = event.clientX; prevY = event.clientY; isMouseDown = true; } function mouseMove(event) { if (!isMouseDown) { return; } var element = document.getElementById("div1"); element.style.left = (element.offsetLeft + (event.clientX - prevX)) + "px"; element.style.top = (element.offsetTop + (event.clientY - prevY)) + "px"; prevX = event.clientX; prevY = event.clientY; } function mouseUp(event) { isMouseDown = false; }

  4. Cleaner Implementation <body> <div id="div1">Drag Me!</div> <div id="div2">Drag Me Too!</div> <script type="text/javascript" src="dragger.js" /> <script type="text/javascript"> //<![CDATA[ new Dragger("div1"); new Dragger("div2"); //]]> </script> </body>} CS 142 Lecture Notes: Events

  5. Dragger.js, part 1 function Dragger(id) { this.isMouseDown = false; this.element = document.getElementById(id); varobj = this; this.element.onmousedown = function(event) { obj.mouseDown(event); } } Dragger.prototype.mouseDown= function(event) { varobj = this; this.oldMoveHandler = document.body.onmousemove; document.body.onmousemove= function(event) { obj.mouseMove(event); } this.oldUpHandler = document.body.onmouseup; document.body.onmouseup= function(event) { obj.mouseUp(event); } this.prevX= event.clientX; this.prevY = event.clientY; this.isMouseDown = true; } CS 142 Lecture Notes: Events

  6. Dragger.js, part 2 Dragger.prototype.mouseMove = function(event) { if (!this.isMouseDown) { return; } this.element.style.left = (this.element.offsetLeft + (event.clientX - this.prevX)) + "px"; this.element.style.top = (this.element.offsetTop + (event.clientY - this.prevY)) + "px"; this.prevX = event.clientX; this.prevY = event.clientY; } Dragger.prototype.mouseUp = function(event) { this.isMouseDown = false; document.body.onmousemove= this.oldMoveHandler; document.body.onmouseup= this.oldUpHandler; } CS 142 Lecture Notes: Events

  7. Which Element Gets Event? <body> <table> <tr> <td>xyz</td> </tr> </table> </body> Click on this CS 142 Lecture Notes: Events

  8. CS 142 Lecture Notes: Cookies

More Related