js 实现的拖动效果的实例

在JS中返回值的方式有多种

如：
return <T>;

return X:<T>,y:<T>;

鼠标的位置处理有如下方式：
document.onmousemove = mouseMove;
document.onmousedown = mouseDown;
document.onmouseup = mouseUp;

如下几个比较有用的函数：
appendChild()
removeChild()
offSetParent
getAttribute()
setAttribute()
currentStyle
push()

从如下程序中总结得来的：

var Demos = [];
var nDemos = 8;

// Demo variables
// iMouseDown represents the current mouse button state: up or down
/*
lMouseState represents the previous mouse button state so that we can
check for button clicks and button releases:

if(iMouseDown && !lMouseState) // button just clicked!
if(!iMouseDown && lMouseState) // button just released!
*/
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;
var nImg        = new Image();

nImg.src = ‘images/drag_drop_poof.gif‘;

// Demo1 variables
var D1Target = 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 getPosition(e){
var left = 0;
var top = 0;
while (e.offsetParent){
  left += e.offsetLeft + (e.currentStyle?(parseInt(e.currentStyle.borderLeftWidth)).NaN0():0);
  top += e.offsetTop + (e.currentStyle?(parseInt(e.currentStyle.borderTopWidth)).NaN0():0);
  e     = e.offsetParent;
}

left += e.offsetLeft + (e.currentStyle?(parseInt(e.currentStyle.borderLeftWidth)).NaN0():0);
top += e.offsetTop + (e.currentStyle?(parseInt(e.currentStyle.borderTopWidth)).NaN0():0);

return {x:left, y:top};

}

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 writeHistory(object, message){
if(!object || !object.parentNode || !object.parentNode.getAttribute) return;
var historyDiv = object.parentNode.getAttribute(‘history‘);
if(historyDiv){
  historyDiv = document.getElementById(historyDiv);
  historyDiv.appendChild(document.createTextNode(object.id+‘: ‘+message));
  historyDiv.appendChild(document.createElement(‘BR‘));

historyDiv.scrollTop += 50;
}
}

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 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);

if(Demos[0] || Demos[4]){
  // mouseOut event - fires if the item the mouse is on has changed
  if(lastTarget && (target!==lastTarget)){
   writeHistory(lastTarget, ‘Mouse Out Fired‘);

   // 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){
    writeHistory(target, ‘Mouse Over Fired‘);

    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){
    writeHistory(target, ‘Start Dragging‘);

// 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((parseInt(getAttribute(‘startLeft‘))                                           < xPos) &&
      (parseInt(getAttribute(‘startTop‘))                                            < yPos) &&
      ((parseInt(getAttribute(‘startLeft‘)) + parseInt(getAttribute(‘startWidth‘))) > xPos) &&
      ((parseInt(getAttribute(‘startTop‘)) + parseInt(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){
    if(activeCont!=curTarget.parentNode){
     writeHistory(curTarget, ‘Moved into ‘+activeCont.id);
    }

// 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]                                                  &&
       ((parseInt(getAttribute(‘startLeft‘)) + parseInt(getAttribute(‘startWidth‘))) > xPos) &&
       ((parseInt(getAttribute(‘startTop‘)) + parseInt(getAttribute(‘startHeight‘))) > yPos)){
        beforeNode = activeCont.childNodes[i];
      }
     }
    }

    // the item being dragged belongs before another item
    if(beforeNode){
     if(beforeNode!=curTarget.nextSibling){
      writeHistory(curTarget, ‘Inserted Before ‘+beforeNode.id);

activeCont.insertBefore(curTarget, beforeNode);
}

    // the item being dragged belongs at the end of the current container
    } else {
     if((curTarget.nextSibling) || (curTarget.parentNode!=activeCont)){
      writeHistory(curTarget, ‘Inserted at end of ‘+activeCont.id);

      activeCont.appendChild(curTarget);
     }
    }

    // the timeout is here because the container doesn‘t "immediately" resize
    setTimeout(function(){
    var contPos = getPosition(activeCont);
    activeCont.setAttribute(‘startWidth‘, parseInt(activeCont.offsetWidth));
    activeCont.setAttribute(‘startHeight‘, parseInt(activeCont.offsetHeight));
    activeCont.setAttribute(‘startLeft‘,   contPos.x);
    activeCont.setAttribute(‘startTop‘,    contPos.y);}, 5);

    // make our drag item visible
    if(curTarget.style.display!=‘‘){
     writeHistory(curTarget, ‘Made Visible‘);
     curTarget.style.display    = ‘‘;
     curTarget.style.visibility = ‘hidden‘;
    }
   } else {

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

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

  // mouseMove target
  lastTarget = target;
}
if(Demos[2]){
  document.getElementById(‘MouseXPosition‘).value = mousePos.x;
  document.getElementById(‘MouseYPosition‘).value = mousePos.y;
}

if(dragObject){
  dragObject.style.position = ‘absolute‘;
  dragObject.style.top      = mousePos.y - mouseOffset.y;
  dragObject.style.left     = mousePos.x - mouseOffset.x;
}

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

// this prevents items on the page from being highlighted while dragging
if(curTarget || dragObject) return false;
}

function mouseUp(ev){

if(Demos[0] || Demos[4]){
if(curTarget){
writeHistory(curTarget, ‘Mouse Up Fired‘);

   dragHelper.style.display = ‘none‘;
   if(curTarget.style.display == ‘none‘){
    if(rootSibling){
     rootParent.insertBefore(curTarget, rootSibling);
    } else {
     rootParent.appendChild(curTarget);
    }
   }
   curTarget.style.display    = ‘‘;
   curTarget.style.visibility = ‘visible‘;
  }
  curTarget = null;
}
if(Demos[6] && dragObject){
  ev           = ev || window.event;
  var mousePos = mouseCoords(ev);

dragObject = null;

iMouseDown = false;
}

function mouseDown(ev){
ev = ev || window.event;
var target = ev.target || ev.srcElement;

iMouseDown = true;
if(Demos[0] || Demos[4]){
  if(lastTarget){
   writeHistory(lastTarget, ‘Mouse Down Fired‘);
  }
}
if(target.onmousedown || target.getAttribute(‘DragObj‘)){
  return false;
}
}

function makeDraggable(item){
if(!item) return;
item.onmousedown = function(ev){
  dragObject = this;
  mouseOffset = getMouseOffset(this, ev);
  return false;
}
}

function makeClickable(item){
if(!item) return;
item.onmousedown = function(ev){
document.getElementById(‘ClickImage‘).value = this.name;
}
}

function addDropTarget(item, target){
item.setAttribute(‘droptarget‘, target);
}

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

window.onload = function(){
for(var i=0; i<nDemos; i++){
Demos[i] = document.getElementById(‘Demo‘+i);
}

if(Demos[0]){
  CreateDragContainer(document.getElementById(‘DragContainer1‘), document.getElementById(‘DragContainer2‘), document.getElementById(‘DragContainer3‘));
  CreateDragContainer(document.getElementById(‘DragContainer7‘));
  CreateDragContainer(document.getElementById(‘DragContainer8‘));
}
if(Demos[4]){
  CreateDragContainer(document.getElementById(‘DragContainer4‘), document.getElementById(‘DragContainer5‘), document.getElementById(‘DragContainer6‘));
}
if(Demos[0] || Demos[4]){
  // Create our helper object that will show the item while dragging
  dragHelper = document.createElement(‘DIV‘);
  dragHelper.style.cssText = ‘position:absolute;display:none;‘;

  addDropTarget(document.getElementById(‘DragImage9‘), ‘TrashImage1‘);
  addDropTarget(document.getElementById(‘DragImage10‘), ‘TrashImage1‘);
  addDropTarget(document.getElementById(‘DragImage11‘), ‘TrashImage1‘);
  addDropTarget(document.getElementById(‘DragImage12‘), ‘TrashImage1‘);
}
if(Demos[3]){
  makeClickable(document.getElementById(‘ClickImage1‘));
  makeClickable(document.getElementById(‘ClickImage2‘));
  makeClickable(document.getElementById(‘ClickImage3‘));
  makeClickable(document.getElementById(‘ClickImage4‘));
}
}

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