dragdrop.js

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    var offsets = Position.cumulativeOffset(this.element);
    offsets[0] -= this.currentLeft();
    offsets[1] -= this.currentTop();
    var style = this.element.style;
    if((!this.options.constraint) || (this.options.constraint=='horizontal'))
      style.left = (pointer[0] - offsets[0] - this.offsetX) + "px";
    if((!this.options.constraint) || (this.options.constraint=='vertical'))
      style.top  = (pointer[1] - offsets[1] - this.offsetY) + "px";
    if(style.visibility=="hidden") style.visibility = ""; // fix gecko rendering
  },
  update: function(event) {
   if(this.active) {
      if(!this.dragging) {
        var style = this.element.style;
        this.dragging = true;
        if(style.position=="") style.position = "relative";
        style.zIndex = this.options.zindex;
        
        if(this.options.ghosting) {
          this._clone = this.element.cloneNode(true);
          Position.absolutize(this.element);
          this.element.parentNode.insertBefore(this._clone, this.element);
        }
        
        Draggables.notify('onStart', this);
        if(this.options.starteffect) this.options.starteffect(this.element);
      }
      
      Droppables.show(event, this.element);
      this.draw(event);
      if(this.options.change) this.options.change(this);
      
      // fix AppleWebKit rendering
      if(navigator.appVersion.indexOf('AppleWebKit')>0) window.scrollBy(0,0); 
      
      Event.stop(event);
   }
  }
}

/*--------------------------------------------------------------------------*/

SortableObserver = Class.create();
SortableObserver.prototype = {
  initialize: function(element, observer) {
    this.element   = $(element);
    this.observer  = observer;
    this.lastValue = Sortable.serialize(this.element);
  },
  onStart: function() {
    this.lastValue = Sortable.serialize(this.element);
  },
  onEnd: function() {
    Sortable.unmark();
    if(this.lastValue != Sortable.serialize(this.element))
      this.observer(this.element)
  }
}

Sortable = {
  sortables: new Array(),
  options: function(element){
    var element = $(element);
    for(var i=0;i<this.sortables.length;i++)
      if(this.sortables[i].element == element)
        return this.sortables[i];
    return null;        
  },
  destroy: function(element){
    var element = $(element);
    for(var i=0;i<this.sortables.length;i++) {
      if(this.sortables[i].element == element) {
        var s = this.sortables[i];
        Draggables.removeObserver(s.element);
        for(var j=0;j<s.droppables.length;j++)
          Droppables.remove(s.droppables[j]);
        for(var j=0;j<s.draggables.length;j++)
          s.draggables[j].destroy();
        this.sortables.splice(i,1);
      }
    }
  },
  create: function(element) {
    var element = $(element);
    var options = Object.extend({ 
      element:     element,
      tag:         'li',       // assumes li children, override with tag: 'tagname'
      dropOnEmpty: false,
      tree:        false,      // fixme: unimplemented
      overlap:     'vertical', // one of 'vertical', 'horizontal'
      constraint:  'vertical', // one of 'vertical', 'horizontal', false
      containment: element,    // also takes array of elements (or id's); or false
      handle:      false,      // or a CSS class
      only:        false,
      hoverclass:  null,
      ghosting:    false,
      onChange:    function() {},
      onUpdate:    function() {}
    }, arguments[1] || {});
    
    // clear any old sortable with same element
    this.destroy(element);
    
    // build options for the draggables
    var options_for_draggable = {
      revert:      true,
      ghosting:    options.ghosting,
      constraint:  options.constraint,
      handle:      handle };
   
    if(options.starteffect)
      options_for_draggable.starteffect = options.starteffect;
   
    if(options.reverteffect)
      options_for_draggable.reverteffect = options.reverteffect;
    else
      if(options.ghosting) options_for_draggable.reverteffect = function(element) {
        element.style.top  = 0;
        element.style.left = 0;
      };
   
    if(options.endeffect)
      options_for_draggable.endeffect = options.endeffect;
   
    if(options.zindex)
      options_for_draggable.zindex = options.zindex;
    
    // build options for the droppables  
    var options_for_droppable = {
      overlap:     options.overlap,
      containment: options.containment,
      hoverclass:  options.hoverclass,
      onHover:     Sortable.onHover,
      greedy:      !options.dropOnEmpty
    }

    // fix for gecko engine
    Element.cleanWhitespace(element); 
    
    options.draggables = [];
    options.droppables = [];
    
    // make it so
    
    // drop on empty handling
    if(options.dropOnEmpty) {
      Droppables.add(element,
        {containment: options.containment, onHover: Sortable.onEmptyHover, greedy: false});
      options.droppables.push(element);
    }
     
    var elements = this.findElements(element, options);
    if(elements) {
      for (var i = 0; i < elements.length; i++) {
        // handles are per-draggable
        var handle = options.handle ? 
          Element.Class.childrenWith(elements[i], options.handle)[0] : elements[i];
            options.draggables.push(new Draggable(elements[i], Object.extend(options_for_draggable, { handle: handle })));
            Droppables.add(elements[i], options_for_droppable);
        
        options.droppables.push(elements[i]);
      }
    }
   
    // keep reference
    this.sortables.push(options);
    
    // for onupdate
    Draggables.addObserver(new SortableObserver(element, options.onUpdate));

  },
  
  // return all suitable-for-sortable elements in a guaranteed order
  findElements: function(element, options) {
    if(!element.hasChildNodes()) return null;
    var elements = [];
    var children = element.childNodes;
    for(var i = 0; i<children.length; i++) {
      if(children[i].tagName && children[i].tagName==options.tag.toUpperCase() &&
        (!options.only || (Element.Class.has(children[i], options.only))))
          elements.push(children[i]);
      if(options.tree) {
        var grandchildren = this.findElements(children[i], options);
        if(grandchildren) elements.push(grandchildren);
      }
    }
  
    return (elements.length>0 ? elements.flatten() : null);
  },
  
  onHover: function(element, dropon, overlap) {
    if(overlap>0.5) {
      Sortable.mark(dropon, 'before');
      if(dropon.previousSibling != element) {
        var oldParentNode = element.parentNode;
        element.style.visibility = "hidden"; // fix gecko rendering
        dropon.parentNode.insertBefore(element, dropon);
        if(dropon.parentNode!=oldParentNode && oldParentNode.sortable) 
          oldParentNode.sortable.onChange(element);
        if(dropon.parentNode.sortable)
          dropon.parentNode.sortable.onChange(element);
      }
    } else {
      Sortable.mark(dropon, 'after');
      var nextElement = dropon.nextSibling || null;
      if(nextElement != element) {
        var oldParentNode = element.parentNode;
        element.style.visibility = "hidden"; // fix gecko rendering
        dropon.parentNode.insertBefore(element, nextElement);
        if(dropon.parentNode!=oldParentNode && oldParentNode.sortable) 
          oldParentNode.sortable.onChange(element);
        if(dropon.parentNode.sortable)
          dropon.parentNode.sortable.onChange(element);
      }
    }
  },
  
  onEmptyHover: function(element, dropon) {
    if(element.parentNode!=dropon) {
      dropon.appendChild(element);
    }
  },
  
  unmark: function() {
    if(Sortable._marker) Element.hide(Sortable._marker);
  },
  
  mark: function(dropon, position) {
    // mark on ghosting only
    var sortable = Sortable.options(dropon.parentNode);
    if(sortable && !sortable.ghosting) return; 
    
    if(!Sortable._marker) {
      Sortable._marker = $('dropmarker') || document.createElement('DIV');
      Element.hide(Sortable._marker);
      Element.Class.add(Sortable._marker, 'dropmarker');
      Sortable._marker.style.position = 'absolute';
      document.getElementsByTagName("body").item(0).appendChild(Sortable._marker);
    }    
    var offsets = Position.cumulativeOffset(dropon);
    Sortable._marker.style.top  = offsets[1] + 'px';
    if(position=='after') Sortable._marker.style.top = (offsets[1]+dropon.clientHeight) + 'px';
    Sortable._marker.style.left = offsets[0] + 'px';
    Element.show(Sortable._marker);
  },
  
  serialize: function(element) {
    var element = $(element);
    var sortableOptions = this.options(element);
    var options = Object.extend({
      tag:  sortableOptions.tag,
      only: sortableOptions.only,
      name: element.id
    }, arguments[1] || {});
    
    var items = $(element).childNodes;
    var queryComponents = new Array();
 
    for(var i=0; i<items.length; i++)
      if(items[i].tagName && items[i].tagName==options.tag.toUpperCase() &&
        (!options.only || (Element.Class.has(items[i], options.only))))
        queryComponents.push(
          encodeURIComponent(options.name) + "[]=" + 
          encodeURIComponent(items[i].id.split("_")[1]));

    return queryComponents.join("&");
  }
}