[整理]如何在 JavaScript 中实现拖放

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逍遥游 · 2007-09-13 · via 博客园 - 逍遥游

var mouseOffset = null;
var iMouseDown = false;
var lMouseState = false;
var dragObject = null;

// Demo 0 variables
var DragDrops   = [];
var curTarget   = null;
var lastTarget = null;
var dragHelper = null;
var tempDiv     = null;
var rootParent = null;
var rootSibling = null;

//Number.prototype.NaN0=function(){return isNaN(this)?0:this;}

function CreateDragContainer(){
/*
Create a new "Container Instance" so that items from one "Set" can not
be dragged into items from another "Set"
*/
var cDrag = DragDrops.length;
DragDrops[cDrag] = [];

/*
Each item passed to this function should be a "container". Store each
of these items in our current container
*/
for(var i=0; i<arguments.length; i++){
  var cObj = arguments[i];
  DragDrops[cDrag].push(cObj);
  cObj.setAttribute('DropObj', cDrag);

  /*
  Every top level item in these containers should be draggable. Do this
  by setting the DragObj attribute on each item and then later checking
  this attribute in the mouseMove function
  */
  for(var j=0; j<cObj.childNodes.length; j++){

// Firefox puts in lots of #text nodes...skip these
if(cObj.childNodes[j].nodeName=='#text') continue;

   cObj.childNodes[j].setAttribute('DragObj', cDrag);
  }
}
}
function mouseCoords(ev) {
if(ev.pageX || ev.pageY) {
    return {x:ev.pageX, y:ev.pageY};
}
return {
    x:ev.clientX + document.body.scrollLeft - document.body.clientLeft,
    y:ev.clientY + document.body.scrollTop - document.body.clientTop
};
}
function getMouseOffset(target, ev)   {
ev = ev || window.event;

var docPos = getPosition(target);
var mousePos = mouseCoords(ev);

    return    {x:mousePos.x - docPos.x, y:mousePos.y - docPos.y} ;
}

function getPosition(e)   {
   var left =   0 ;
   var top   =   0 ;

   while (e.offsetParent) {
    left += e.offsetLeft;
    top += e.offsetTop;
    e = e.offsetParent;
}

left += e.offsetLeft;
top += e.offsetTop;

return {x:left, y:top} ;
}

function mouseMove(ev){
ev = ev || window.event;

/*
We are setting target to whatever item the mouse is currently on

Firefox uses event.target here, MSIE uses event.srcElement
*/
var target   = ev.target || ev.srcElement;
var mousePos = mouseCoords(ev);
document.all("posXY").innerText = mousePos.x + " " + mousePos.y
// mouseOut event - fires if the item the mouse is on has changed
if(lastTarget && (target!==lastTarget)){
  // reset the classname for the target element
  var origClass = lastTarget.getAttribute('origClass');
  if(origClass) lastTarget.className = origClass;
}

/*
dragObj is the grouping our item is in (set from the createDragContainer function).
if the item is not in a grouping we ignore it since it can't be dragged with this
script.
*/
var dragObj = target.getAttribute('DragObj');

// if the mouse was moved over an element that is draggable
if(dragObj!=null){

  // mouseOver event - Change the item's class if necessary
  if(target!=lastTarget){
   var oClass = target.getAttribute('overClass');
   if(oClass){
    target.setAttribute('origClass', target.className);
    target.className = oClass;
   }
  }

  // if the user is just starting to drag the element
  if(iMouseDown && !lMouseState){
   // mouseDown target
   curTarget     = target;

   // Record the mouse x and y offset for the element
   rootParent    = curTarget.parentNode;
   rootSibling   = curTarget.nextSibling;

mouseOffset = getMouseOffset(target, ev);

// We remove anything that is in our dragHelper DIV so we can put a new item in it.
for(var i=0; i<dragHelper.childNodes.length; i++) dragHelper.removeChild(dragHelper.childNodes[i]);

   // Make a copy of the current item and put it in our drag helper.
   dragHelper.appendChild(curTarget.cloneNode(true));
   dragHelper.style.display = 'block';

   // set the class on our helper DIV if necessary
   var dragClass = curTarget.getAttribute('dragClass');
   if(dragClass){
    dragHelper.firstChild.className = dragClass;
   }

// disable dragging from our helper DIV (it's already being dragged)
dragHelper.firstChild.removeAttribute('DragObj');

   /*
   Record the current position of all drag/drop targets related
   to the element. We do this here so that we do not have to do
   it on the general mouse move event which fires when the mouse
   moves even 1 pixel. If we don't do this here the script
   would run much slower.
   */
   var dragConts = DragDrops[dragObj];

   /*
   first record the width/height of our drag item. Then hide it since
   it is going to (potentially) be moved out of its parent.
   */
   curTarget.setAttribute('startWidth', parseInt(curTarget.offsetWidth));
   curTarget.setAttribute('startHeight', parseInt(curTarget.offsetHeight));
   curTarget.style.display = 'none';

   // loop through each possible drop container
   for(var i=0; i<dragConts.length; i++){
    with(dragConts[i]){
     var pos = getPosition(dragConts[i]);

/*
save the width, height and position of each container.

     Even though we are saving the width and height of each
     container back to the container this is much faster because
     we are saving the number and do not have to run through
     any calculations again. Also, offsetHeight and offsetWidth
     are both fairly slow. You would never normally notice any
     performance hit from these two functions but our code is
     going to be running hundreds of times each second so every
     little bit helps!

     Note that the biggest performance gain here, by far, comes
     from not having to run through the getPosition function
     hundreds of times.
     */
     setAttribute('startWidth', parseInt(offsetWidth));
     setAttribute('startHeight', parseInt(offsetHeight));
     setAttribute('startLeft',   pos.x);
     setAttribute('startTop',    pos.y);
    }

    // loop through each child element of each container
    for(var j=0; j<dragConts[i].childNodes.length; j++){
     with(dragConts[i].childNodes[j]){
      if((nodeName=='#text') || (dragConts[i].childNodes[j]==curTarget)) continue;

var pos = getPosition(dragConts[i].childNodes[j]);

      // save the width, height and position of each element
      setAttribute('startWidth', parseInt(offsetWidth));
      setAttribute('startHeight', parseInt(offsetHeight));
      setAttribute('startLeft',   pos.x);
      setAttribute('startTop',    pos.y);
     }
    }
   }
  }
}

// If we get in here we are dragging something
if(curTarget){
  // move our helper div to wherever the mouse is (adjusted by mouseOffset)
  dragHelper.style.top = mousePos.y - mouseOffset.y;
  dragHelper.style.left = mousePos.x - mouseOffset.x;

var dragConts = DragDrops[curTarget.getAttribute('DragObj')];
var activeCont = null;

var xPos = mousePos.x - mouseOffset.x + (parseInt(curTarget.getAttribute('startWidth')) /2);
var yPos = mousePos.y - mouseOffset.y + (parseInt(curTarget.getAttribute('startHeight'))/2);

  // check each drop container to see if our target object is "inside" the container
  for(var i=0; i<dragConts.length; i++){
   with(dragConts[i]){
    if(((getAttribute('startLeft'))                               < xPos) &&
     ((getAttribute('startTop'))                                < yPos) &&
     ((getAttribute('startLeft') + getAttribute('startWidth')) > xPos) &&
     ((getAttribute('startTop') + getAttribute('startHeight')) > yPos)){

      /*
      our target is inside of our container so save the container into
      the activeCont variable and then exit the loop since we no longer
      need to check the rest of the containers
      */
      activeCont = dragConts[i];

      // exit the for loop
      break;
    }
   }
  }

  // Our target object is in one of our containers. Check to see where our div belongs
  if(activeCont){
   // beforeNode will hold the first node AFTER where our div belongs
   var beforeNode = null;

   // loop through each child node (skipping text nodes).
   for(var i=activeCont.childNodes.length-1; i>=0; i--){
    with(activeCont.childNodes[i]){
     if(nodeName=='#text') continue;

     // if the current item is "After" the item being dragged
     if(
      curTarget != activeCont.childNodes[i]                              &&
      ((getAttribute('startLeft') + getAttribute('startWidth')) > xPos) &&
      ((getAttribute('startTop') + getAttribute('startHeight')) > yPos)){
       beforeNode = activeCont.childNodes[i];
     }
    }
   }

   // the item being dragged belongs before another item
   if(beforeNode){
    if(beforeNode!=curTarget.nextSibling){
     activeCont.insertBefore(curTarget, beforeNode);
    }

   // the item being dragged belongs at the end of the current container
   } else {
    if((curTarget.nextSibling) || (curTarget.parentNode!=activeCont)){
     activeCont.appendChild(curTarget);
    }
   }

   // make our drag item visible
   if(curTarget.style.display!=''){
    curTarget.style.display = '';
   }
  } else {

   // our drag item is not in a container, so hide it.
   if(curTarget.style.display!='none'){
    curTarget.style.display = 'none';
   }
  }
}

// track the current mouse state so we can compare against it next time
lMouseState = iMouseDown;

// mouseMove target
lastTarget = target;

// track the current mouse state so we can compare against it next time
lMouseState = iMouseDown;

// this helps prevent items on the page from being highlighted while dragging
return false;
}

function mouseUp(ev){
if(curTarget){
// hide our helper object - it is no longer needed
dragHelper.style.display = 'none';

  // if the drag item is invisible put it back where it was before moving it
  if(curTarget.style.display == 'none'){
   if(rootSibling){
    rootParent.insertBefore(curTarget, rootSibling);
   } else {
    rootParent.appendChild(curTarget);
   }
  }

// make sure the drag item is visible
curTarget.style.display = '';
}
curTarget = null;
iMouseDown = false;
}

function mouseDown(){
iMouseDown = true;
if(lastTarget){
return false;
}
}

document.onmousemove = mouseMove;
document.onmousedown = mouseDown;
document.onmouseup = mouseUp;

window.onload = function(){
// Create our helper object that will show the item while dragging
dragHelper = document.createElement('DIV');
dragHelper.style.cssText = 'position:absolute;display:none;';

CreateDragContainer(
  document.getElementById('DragContainer1'),
  document.getElementById('DragContainer2'),
  document.getElementById('DragContainer3')
);

document.body.appendChild(dragHelper);
}
</script>
</HEAD>

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