用Javascript实现鼠标拖拽网页表单 (二)

 

整合所有的功能

最后我们使用所有代码片断，来创建一个完整的拖放函数脚本。我们所要做的第一件事情是DOM操作，如果你对此并不十分熟悉，可以阅读《 JavaScript Primer on DOM Manipulation 》。

接下来的代码创建容器和容器组，使得在这些容器中可以拖动每个元素，这在本文第二个demo的基础上来完成。这段代码能够用来重新规划元素的顺序，将导航窗口放在页面的左侧或右侧，或再加入你所能想到的其他的功能。

我们将使用伪代码来一步步进行讲解，将真实的代码通过注释的方式留给读者查看。

1.当文档第一次被加载时，我们创建一个名为dragHelper的DIV标签，当我们开始移动一个元素的时候，dragHelper将成为一个隐藏元素，可以四处移动。真实的元素并不会被拖动，仅仅使用insertBefore和appendChild来移动。我们在开始的时候隐藏dragHelper。

2.我们创建mouseDown和mouseUp函数。起初，所有的这些函数都假设记录了鼠标按钮的状态，以至于iMouseDown变量在鼠标按下的时候为true，没有按下的时候为false。

3.我们创建一个全局变量DragDrops，以及一个函数CreateDragContainer。DragDrops包含一组相互关联的容器。传入CreateDragContainer的任何变量（代表容器）被组织成一个新的集合，使元素能够在这些容器间自由移动。通过setAttribute，CreateDragContainer函数同样将各容器中的元素绑定在一起。

4.现在我们的代码知道每个元素所在的集合，现在来看mouseMove函数。mouseMove函数首先设置了一个变量target，表示鼠标下面的目标元素，如果这个元素在集合（用getAttribute判断）中就继续下面操作：

4.1.首先，在必要的时候，我们运行一个简单的脚本来改变目标元素的class属性，这样就创造了一个翻动的效果。

4.2.然后我们检查鼠标是否点击（因为我们的代码已经运行到这里），如果事件发生：

4.2.1.设置变量curTarget为当前元素。
4.2.2.记录元素当前在文档中的位置，以便在需要的时候可以将它的值取回。
4.2.3.将当前元素克隆到dragHelper，使得我们能够移动元素的隐藏备份。
4.2.4.因为在dragHelper中我们完全拥有了拖动元素的一个备份，这个元素会始终在鼠标下，我们必须移除dragObj属性，让代码知道dragObj已不在集合中。
4.2.5.我们快速记录集合中每个元素当前的位置、宽度和高度。当元素第一次开始被拖动时，我们仅需做一次这种工作，否则每当鼠标移动的时候我们都必须做一次，甚至一秒内几百次。

4.3.如果鼠标没有点击，要么我们和之前拥有同样的目标元素，要么没有目标元素，不论哪种情况我们都不会做任何事情。

5.现在我们检查curTarget变量。curTarget应该仅包含一个被拖动的对象，因此如果它存在，表示我们正在拖动一个元素：

5.1.移动隐藏DIV到鼠标，这个元素和文章前面所创建的元素一样能够被拖动。

5.2.然后我们检查鼠标是否存在于当前集合中每个容器中。

5.2.1.如果鼠标在某个容器中，我们检查容器中的每个元素，查看我们正拖动的元素属于哪个位置。
5.2.2.然后我们将所拖动的元素放置在容器中另一个元素的前面，或容器的最后位置。
5.2.3.最后我们确定元素可见。

6.剩下的事情就是捕获mouseUp事件：
6.1.首先需要隐藏dragHelper：它不再被需要，因为我们没有拖动任何东西。
6.2.如果拖动的元素是可见的，它已经存在于任何它所属的容器中，所有工作已完成。
6.3.如果拖动的元素不可见，我们将它放回它原来所在的地方。
// 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 nodesskip 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);
}

< div class ="DragContainer" id ="DragContainer1" >
< div class ="DragBox" id ="Item1" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #1

< div class ="DragBox" id ="Item2" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #2

< div class ="DragBox" id ="Item3" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #3

< div class ="DragBox" id ="Item4" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #4

< div class ="DragContainer" id ="DragContainer2" >
< div class ="DragBox" id ="Item5" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #5

< div class ="DragBox" id ="Item6" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #6

< div class ="DragBox" id ="Item7" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #7

< div class ="DragBox" id ="Item8" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #8

< div class ="DragContainer" id ="DragContainer3" >
< div class ="DragBox" id ="Item9" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #9

< div class ="DragBox" id ="Item10" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #10

< div class ="DragBox" id ="Item11" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #11

< div class ="DragBox" id ="Item12" overClass ="OverDragBox" dragClass ="DragDragBox" > Item #12

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