用javascript做拖动布局的思路

function getEvent(){
//同时兼容ie和ff的写法
if(document.all) return window.event;
func=getEvent.caller;
while(func!=null){
var arg0=func.arguments[0];
if(arg0){
if((arg0.constructor==Event || arg0.constructor ==MouseEvent)
|| (typeof(arg0)=="object" && arg0.preventDefault && arg0.stopPropagation)){
return arg0;
}
}
func=func.caller;
}
return null;
}

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 getPosition(ele){
var left = 0;
var top = 0;
while (ele.offsetParent){
left += ele.offsetLeft;
top += ele.offsetTop;
ele = ele.offsetParent;
}
left += ele.offsetLeft;
top += ele.offsetTop;
return {x:left, y:top};
}

var tmpDiv=null;//临时存放拖动对象的div
window.onload=function(){
tmpDiv=document.createElement("div");
tmpDiv.style.cssText = 'position:absolute;display:none;border:1px dotted #FFCC66;';
document.body.appendChild(tmpDiv);
}

var dragObject = null;//拖动的元素(table)
var mouseOffset = null;//鼠标的在拖动元素中的位置
var dragDiv=null;//拖动的table所在的列的div
var eleDivW=null;//拖动的table的父节点(div)的高度
var dragDivLen=null;//拖动的table所在的列的div中用来放置table的div的个数
var DragContainer=["col1","col2","col3"];//用来实现列布局的div的id
//鼠标按下拖动的元素
function mouseDown(elem){
ev=getEvent();
dragObject = elem.parentNode.parentNode.parentNode;//被拖动的table
dragDiv=dragObject.parentNode.parentNode;
//拖动元素所在列里div的个数
dragDivLen=dragDiv.getElementsByTagName("div").length;
mouseOffset = getMouseOffset(dragObject, ev);
eleDivW=dragObject.parentNode.offsetWidth;
dragObject.parentNode.style.border="1px dotted #FFCC66";
return false;
}
//得到鼠标在拖动元素中的位置
function getMouseOffset(target, ev){
var docPos = getPosition(target);
var mousePos = mouseCoords(ev);
return {x:mousePos.x - docPos.x, y:mousePos.y - docPos.y};
}

document.onmousemove = mouseMove;
function mouseMove(){
ev=getEvent();
var mousePos = mouseCoords(ev);
if(dragObject){
dragObject.parentNode.style.display="none";//设置放置被拖动table的div隐藏
//把拖动的table放到临时的div中，并设置其坐标
for(var i=0; i<tmpDiv.childNodes.length; i++) tmpDiv.removeChild(tmpDiv.childNodes[i]);
tmpDiv.appendChild(dragObject.cloneNode(true));
tmpDiv.style.width=eleDivW+"px";
tmpDiv.style.backgroundColor="#FFFFFF";
tmpDiv.style.display="block";
tmpDiv.style.top = (mousePos.y - mouseOffset.y)+"px";
tmpDiv.style.left = (mousePos.x - mouseOffset.x)+"px";
}
return false;
}

document.onmouseup = mouseUp;
//鼠标松开
function mouseUp(){
if(dragObject){
if(dragObject.parentNode.style.display=="none") dragObject.parentNode.style.display="block";
dragObject.parentNode.style.border="1px solid #FFCC66";
tmpDiv.style.display="none";
//这里是判断当列里有可拖动的元素时清除前面设置的高度值20px
for(var m=0;m<DragContainer.length;m++){
var colDiv=document.getElementById(DragContainer[m]);
var colDivLen=colDiv.getElementsByTagName("div").length
var colSty=colDiv.getAttribute("style");
if(colDivLen>0&&colSty!=null){
colDiv.removeAttribute("style");
break;
}
}
dragObject=null;
}
}

function mouseMove(){
ev=getEvent();
var mousePos = mouseCoords(ev);
if(dragObject){
//可拖动的个数为1,说明拖动后此列就没有拖动元素，为避免此列没有高度而不见，所以设置其高度为20px
if(dragDivLen==1) dragDiv.style.height="20px";
dragObject.parentNode.style.display="none";
//把拖动的元素加入到临时的tmpDiv中，并设置tmpDiv坐标
for(var i=0; i<tmpDiv.childNodes.length; i++) tmpDiv.removeChild(tmpDiv.childNodes[i]);
tmpDiv.appendChild(dragObject.cloneNode(true));
tmpDiv.style.width=eleDivW+"px";
tmpDiv.style.backgroundColor="#FFFFFF";
tmpDiv.style.display="block";
tmpDiv.style.top = (mousePos.y - mouseOffset.y)+"px";
tmpDiv.style.left = (mousePos.x - mouseOffset.x)+"px";
//被拖动对象的中心点的坐标
var dragObjCntX=mousePos.x - mouseOffset.x+parseInt(dragObject.offsetWidth)/2;
var dragObjCntY=mousePos.y - mouseOffset.y+parseInt(dragObject.offsetHeight)/2;
//判断tmpDiv所在的列
var dragConLen=DragContainer.length;
for(var i=0;i<dragConLen;i++){
var curContainer=document.getElementById(DragContainer[i]);
var dcPos=getPosition(curContainer);
var dcPosMinX=dcPos.x;
var dcPosMinY=dcPos.y;
var dcWidth=curContainer.offsetWidth;
var dcHeight=curContainer.offsetHeight;
var dcPosMaxX=dcPosMinX+dcWidth;
var dcPosMaxY=dcPosMinY+dcHeight;
if(dragObjCntX>dcPosMinX&&dragObjCntX<dcPosMaxX&&dragObjCntY>dcPosMinY&&dragObjCntY<dcPosMaxY){
var activeContainer=curContainer;
break;
}
}
}
//判断tmpDiv在此列哪个区块范围内
if(activeContainer){
var beforNode=null;
var sDiv=activeContainer.getElementsByTagName("div")
var acChiLen=sDiv.length;
for(j=acChiLen-1;j>=0;j--){
var activeDiv=sDiv[j];
if(activeDiv){
var activeDivPos=getPosition(activeDiv);
var activeDivMinX=activeDivPos.x;
var activeDivMinY=activeDivPos.y;
var activeDivMaxX=activeDivMinX+activeDiv.offsetWidth;
var activeDivMaxY=activeDivMinY+activeDiv.offsetHeight;
if(activeDivMaxX>dragObjCntX&&activeDivMaxY>dragObjCntY){
//if(dragObjCntX>activeDivMinX&&dragObjCntX<activeDivMaxX&&dragObjCntY>activeDivMinY&&dragObjCntY<activeDivMaxY){
beforNode=activeDiv;
}
}
}
//若此区块存在，就在此区块前插入拖动元素
if(beforNode!=null){
if(dragObject.parentNode!=beforNode){
curContainer.insertBefore(dragObject.parentNode,beforNode);
dragObject.parentNode.style.display="block";
//document.getElementById("test").value=curContainer.id;
}
}
//不存在就在所在列插入拖动元素
else{
curContainer.appendChild(dragObject.parentNode);
dragObject.parentNode.style.display="block";
}
}
return false;
}