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Web Directions Code 12: Drag and Drop

Web Directions Code 12: Drag and Drop

A little primer to native HTML5 drag and drop.

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makenosound

May 24, 2012
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  1. Hello Friday, 25 May 12

  2. Drag ’N’ DROp Friday, 25 May 12

  3. WHY? Friday, 25 May 12 * Different user-interface models —

    why are we bothering? * Can really make a graphical user interface feel alive. * Simple, but often overlooked.
  4. Friday, 25 May 12 * In web design we expose

    the underlying structure of our applications. * Users don’t care. * Computer interfaces are abstractions. * Drag and drop takes some of the abstraction away. * Touch interfaces more intuitive because the separation between action and effect is small.
  5. Friday, 25 May 12 * All the major JavaScript libraries

    have supporting plugins or UI libraries that include some sort of drag and drop components * jQuery UI * Dojo * Mootools * None of them use the native APIs.
  6. Friday, 25 May 12 * Added to the HTML5 spec.

    * Specification is really a reverse-engineered version of the Internet Explorer 5 implementation of drag and drop.
  7. Friday, 25 May 12 * This is a Drag and

    Drop tutorial from 2000 that is still relevant.
  8. Friday, 25 May 12 * Desktop browser support for drag

    and drop is generally *excellent* * Mobile less so.
  9. <div  draggable='true'>Drag  me!</div> Friday, 25 May 12 * This is

    how you make something draggable. * Set draggable attribute to `true` * Same functionality you'll see in most browsers when dragging anchors or images * We can add functionality to our draggable objects is through the JavaScript API.
  10. dragstart drag dragenter dragleave dragover dragend drop Friday, 25 May

    12 * API has 7 events
  11. // Handle the 'dragstart' event var onDragStart = function(e) {

    $(this).addClass('dragging'); } $('body').on('dragstart', '[draggable]', onDragStart); Friday, 25 May 12 * Simple event listener syntax (using jQuery). * `this` in dragstart callback is the element being dragged.
  12. var onDragStart = function(e) { $(this).addClass('dragging'); } var onDragEnd =

    function(e) { $(this).removeClass('dragging'); } var onDragEnter = function(e) { $(this).addClass('over'); } var onDragLeave = function(e) { $(this).removeClass('over'); } Friday, 25 May 12
  13. Drop it like it’s hot Friday, 25 May 12 *

    Default droppable targets in most browsers: inputs, textareas, and contenteditable regions. * The spec also includes a `dropzone` attribute. Only supported by Opera. * We can use the `drop` event.
  14. var onDragEnter = function(e) { // You *must* cancel the

    default event to be able to drop e.preventDefault(); } var onDragOver = function(e) { // You *must* cancel the default event to be able to drop e.preventDefault(); } Friday, 25 May 12 * Gotchas: for the drop event to fire you need to cancel both the `dragover` and `dragenter` events. If you don't do this then *no drop events will ever fire*.
  15. // What are we draggin’? var draggedElement; var onDragStart =

    function(e) { // Keep track of the draggable draggedElement = this; e.originalEvent.dataTransfer.setData('text/html', this.innerHTML); } var onDrop = function(e) { // Change places! $(draggedElement).html( $(this).html() ); // Pull out the transferred data $(this).html( e.originalEvent.dataTransfer.getData('text/html') ); } $('body') .on('drop', '[data-behaviour~="droppable"]', onDrop) .on('dragstart', '[draggable]', onDragStart); Friday, 25 May 12 * `dataTransfer` object is the secret. * Lets you transfer data around. * A setData and getData function. * setData takes two arguments, a data type, and then the data itself. * In the drop event we get access to that same dataTransfer object.
  16. dataTransfer.dropEffect = 'copy' dataTransfer.effectAllowed = 'move' dataTransfer.setDragImage(element, x, y) dataTransfer.addElement(element)

    Friday, 25 May 12 * The dataTransfer object has a other properties and methods. * Drop effect lets you specify the kind of operation: copy, move, or link elements. * Effect allowed lets dropabbles specify what kind of operation they'll handle. * Set drag image lets you use an image instead of the default draggable element as the "ghost" element. * Add element lets you do the same with an arbitrary DOM element. * Some of these are broken across browsers
  17. Friday, 25 May 12 * Drag and Drop isn't limited

    to data that's in the page. * We can also drag files from the desktop and then manipulate that data. * Combine drag and drop with other HTML5 APIs like FileReader or FileList that allow us to parse and handle the dropped file data.
  18. Friday, 25 May 12 * Fontdragr is a nice example

    from Ryan Seddon * Allows you to drag and drop font files from your computer onto the browser window. * Converts them with the FileReader API to a data URI. * Lets you override page styles with type from your own computer. * Scope for using drag and drop and other APIs to reduce the friction between the your web app and the users desktop environment.
  19. THANKS Friday, 25 May 12 @makenosound