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我觉得变化不大代码，使我有这样的代码，这样，A链接到我们如何使用JavaScript拖放图片？
代码：
function Position(x, y)
{
this.X = x;
this.Y = y;
this.Add = function(val)
{
var newPos = new Position(this.X, this.Y);
if(val != null)
{
if(!isNaN(val.X))
newPos.X += val.X;
if(!isNaN(val.Y))
newPos.Y += val.Y
}
return newPos;
}
this.Subtract = function(val)
{
var newPos = new Position(this.X, this.Y);
if(val != null)
{
if(!isNaN(val.X))
newPos.X -= val.X;
if(!isNaN(val.Y))
newPos.Y -= val.Y
}
return newPos;
}
this.Min = function(val)
{
var newPos = new Position(this.X, this.Y)
if(val == null)
return newPos;
if(!isNaN(val.X) && this.X > val.X)
newPos.X = val.X;
if(!isNaN(val.Y) && this.Y > val.Y)
newPos.Y = val.Y;
return newPos;
}
this.Max = function(val)
{
var newPos = new Position(this.X, this.Y)
if(val == null)
return newPos;
if(!isNaN(val.X) && this.X < val.X)
newPos.X = val.X;
if(!isNaN(val.Y) && this.Y < val.Y)
newPos.Y = val.Y;
return newPos;
}
this.Bound = function(lower, upper)
{
var newPos = this.Max(lower);
return newPos.Min(upper);
}
this.Check = function()
{
var newPos = new Position(this.X, this.Y);
if(isNaN(newPos.X))
newPos.X = 0;
if(isNaN(newPos.Y))
newPos.Y = 0;
return newPos;
}
this.Apply = function(element)
{
if(typeof(element) == "string")
element = document.getElementById(element);
if(element == null)
return;
if(!isNaN(this.X))
element.style.left = this.X + 'px';
if(!isNaN(this.Y))
element.style.top = this.Y + 'px';
}
}
function hookEvent(element, eventName, callback)
{
if(typeof(element) == "string")
element = document.getElementById(element);
if(element == null)
return;
if(element.addEventListener)
{
element.addEventListener(eventName, callback, false);
}
else if(element.attachEvent)
element.attachEvent("on" + eventName, callback);
}
function unhookEvent(element, eventName, callback)
{
if(typeof(element) == "string")
element = document.getElementById(element);
if(element == null)
return;
if(element.removeEventListener)
element.removeEventListener(eventName, callback, false);
else if(element.detachEvent)
element.detachEvent("on" + eventName, callback);
}
function cancelEvent(e)
{
e = e ? e : window.event;
if(e.stopPropagation)
e.stopPropagation();
if(e.preventDefault)
e.preventDefault();
e.cancelBubble = true;
e.cancel = true;
e.returnValue = false;
return false;
}
function getMousePos(eventObj)
{
eventObj = eventObj ? eventObj : window.event;
var pos;
if(isNaN(eventObj.layerX))
pos = new Position(eventObj.offsetX, eventObj.offsetY);
else
pos = new Position(eventObj.layerX, eventObj.layerY);
return correctOffset(pos, pointerOffset, true);
}
function getEventTarget(e)
{
e = e ? e : window.event;
return e.target ? e.target : e.srcElement;
}
function absoluteCursorPostion(eventObj)
{
eventObj = eventObj ? eventObj : window.event;
if(isNaN(window.scrollX))
return new Position(eventObj.clientX + document.documentElement.scrollLeft + document.body.scrollLeft,
eventObj.clientY + document.documentElement.scrollTop + document.body.scrollTop);
else
return new Position(eventObj.clientX + window.scrollX, eventObj.clientY + window.scrollY);
}
function dragObject(element, attachElement, lowerBound, upperBound, startCallback, moveCallback, endCallback, attachLater)
{
if(typeof(element) == "string")
element = document.getElementById(element);
if(element == null)
return;
var cursorStartPos = null;
var elementStartPos = null;
var dragging = false;
var listening = false;
var disposed = false;
function dragStart(eventObj)
{
if(dragging || !listening || disposed) return;
dragging = true;
if(startCallback != null)
startCallback(eventObj, element);
cursorStartPos = absoluteCursorPostion(eventObj);
elementStartPos = new Position(parseInt(element.style.left), parseInt(element.style.top));
elementStartPos = elementStartPos.Check();
hookEvent(document, "mousemove", dragGo);
hookEvent(document, "mouseup", dragStopHook);
return cancelEvent(eventObj);
}
function dragGo(eventObj)
{
if(!dragging || disposed) return;
var newPos = absoluteCursorPostion(eventObj);
newPos = newPos.Add(elementStartPos).Subtract(cursorStartPos);
newPos = newPos.Bound(lowerBound, upperBound)
newPos.Apply(element);
if(moveCallback != null)
moveCallback(newPos, element);
return cancelEvent(eventObj);
}
function dragStopHook(eventObj)
{
dragStop();
return cancelEvent(eventObj);
}
function dragStop()
{
if(!dragging || disposed) return;
unhookEvent(document, "mousemove", dragGo);
unhookEvent(document, "mouseup", dragStopHook);
cursorStartPos = null;
elementStartPos = null;
if(endCallback != null)
endCallback(element);
dragging = false;
}
this.Dispose = function()
{
if(disposed) return;
this.StopListening(true);
element = null;
attachElement = null
lowerBound = null;
upperBound = null;
startCallback = null;
moveCallback = null
endCallback = null;
disposed = true;
}
this.GetLowerBound = function()
{ return lowerBound; }
this.GetUpperBound = function()
{ return upperBound; }
this.StartListening = function()
{
if(listening || disposed) return;
listening = true;
hookEvent(attachElement, "mousedown", dragStart);
}
this.StopListening = function(stopCurrentDragging)
{
if(!listening || disposed) return;
unhookEvent(attachElement, "mousedown", dragStart);
listening = false;
if(stopCurrentDragging && dragging)
dragStop();
}
this.IsDragging = function(){ return dragging; }
this.IsListening = function() { return listening; }
this.IsDisposed = function() { return disposed; }
if(typeof(attachElement) == "string")
attachElement = document.getElementById(attachElement);
if(attachElement == null)
attachElement = element;
if(!attachLater)
this.StartListening();
}
var el = document.getElementById('draggableElement');
var leftEdge = el.parentNode.clientWidth - el.clientWidth;
var topEdge = el.parentNode.clientHeight - el.clientHeight;
var dragObj = new dragObject(el, null, new Position(leftEdge, topEdge), new Position(0, 0));
，有2件事，我解决不了：
当我们拖动和移动大图像时，我们如何移动小图像？
拖动图片时，鼠标不应该移出父div？