我刚刚尝试了创建启用拖放功能的演练。我遵循了http://www.webreference.com/programming/javascript/mk/column2/index.html上的指南
即使指南写得很好，我也无法让它发挥作用，这里有什么明显的错误吗？我的所有代码都粘贴在下面，指南作者的评论也在那里澄清。当我运行页面时会显示所有项目，但当我尝试移动它们时没有任何反应。
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<script type="text/javascript">
// 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;
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 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);
// 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);
}
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
};
}
</script>
<title>Drag and drop test</title>
</head>
<body>
<form id="form1" runat="server">
<!--the mouse over and dragging class are defined on each item-->
<div class="DragContainer" id="DragContainer1">
<div class="DragBox" id="Item1" overClass="OverDragBox" dragClass="DragDragBox">Item #1</div>
<div class="DragBox" id="Item2" overClass="OverDragBox" dragClass="DragDragBox">Item #2</div>
<div class="DragBox" id="Item3" overClass="OverDragBox" dragClass="DragDragBox">Item #3</div>
<div class="DragBox" id="Item4" overClass="OverDragBox" dragClass="DragDragBox">Item #4</div>
</div>
<div class="DragContainer" id="DragContainer2">
<div class="DragBox" id="Item5" overClass="OverDragBox" dragClass="DragDragBox">Item #5</div>
<div class="DragBox" id="Item6" overClass="OverDragBox" dragClass="DragDragBox">Item #6</div>
<div class="DragBox" id="Item7" overClass="OverDragBox" dragClass="DragDragBox">Item #7</div>
<div class="DragBox" id="Item8" overClass="OverDragBox" dragClass="DragDragBox">Item #8</div>
</div>
<div class="DragContainer" id="DragContainer3">
<div class="DragBox" id="Item9" overClass="OverDragBox" dragClass="DragDragBox">Item #9</div>
<div class="DragBox" id="Item10" overClass="OverDragBox" dragClass="DragDragBox">Item #10</div>
<div class="DragBox" id="Item11" overClass="OverDragBox" dragClass="DragDragBox">Item #11</div>
<div class="DragBox" id="Item12" overClass="OverDragBox" dragClass="DragDragBox">Item #12</div>
</div>
</form>
</body>
</html>