探索javascript----拖拽

时间：2023-03-08 22:09:06
<!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>

    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

    <title>完美拖拽</title>

    <style type="text/css">

        html,body{overflow:hidden;}

        body,div,h2,p{margin:0;padding:0;}

        body{color:#fff;background:#000;font:12px/2 Arial;}

        p{padding:0 10px;margin-top:10px;}

        span{color:#ff0;padding-left:5px;}

        #box{position:absolute;width:300px;height:150px;background:#333;border:2px solid #ccc;top:50%;left:50%;margin:-75px 0 0 -150px;}

        #box h2{height:25px;cursor:move;background:#222;border-bottom:2px solid #ccc;text-align:right;padding:0 10px;}

        #box h2 a{color:#fff;font:12px/25px Arial;text-decoration:none;outline:none;}

    </style>

    <script>

        window.onload=function(){

            var oBox=document.getElementById("box");

            var oH=oBox.getElementsByTagName("h2")[0];

            var oA=oBox.getElementsByTagName("a")[0];

            var aSpan=oBox.getElementsByTagName("span");

            var aPos=[{x:oBox.offsetLeft,y:oBox.offsetTop}];

            var bDrag=false;

            var disX=disY=0;

            oH.onmousedown=function(ev){

                var oEv=ev||window.event;

                bDrag=true;

                aPos.push({x:oBox.offsetLeft,y:oBox.offsetTop});

                disX=oEv.clientX-oBox.offsetLeft;

                disY=oEv.clientY-oBox.offsetTop;

                this.setCapture&&this.setCapture();

                return false;

            };

            document.onmousemove=function(ev){

                if (!bDrag) return;

                var oEv=ev||window.event;

                var iL=oEv.clientX-disX;

                var iT=oEv.clientY-disY;

                var iMaxL=document.documentElement.clientWidth-oBox.offsetWidth;

                var iMaxT=document.documentElement.clientHeight-oBox.offsetHeight;

                iL=iL<0?0:iL;

                iT=iT<0?0:iT;

                iL=iL>iMaxL?iMaxL:iL;

                iT=iT>iMaxT?iMaxT:iT;

                oBox.style.marginTop=oBox.style.marginLeft=0;

                oBox.style.left=iL+"px";

                oBox.style.top=iT+"px";

                aPos.push({x:iL,y:iT});

                status();

                return false;

            };

            document.onmouseup=window.onblur=oH.onlosecapture=function(){//window.onblur表示当前窗口失去焦点即激活了其他线程的窗口

                bDrag=false;

                this.releaseCapture&&this.releaseCapture();

                status()

            };

            //回放

            oA.onclick=function(){

                var oPos=play=null;

                if(aPos.length==1) return;

                play=setInterval(function(){

                    oPos=aPos.pop();

                    oPos?(oBox.style.left=oPos.x+"px",oBox.style.top=oPos.y+"px", status()):clearInterval(play);

                },50);

                this.focus=false;

                return false;

            };

            oA.onmousedown=function(ev){

                (ev||window.event).cancelBubble=true;

            };

            function status(){

                aSpan[0].innerHTML=bDrag;

                aSpan[1].innerHTML=oBox.offsetLeft;

                aSpan[2].innerHTML=oBox.offsetTop;

            }

            status();

        };

//心得：用bDrag来独立move和up函数（不同嵌套在down函数里）

//     在临界值的处理里，先把最值算出来再和最值比较再赋值

//     三目运算符里可以写多条语句，用","隔开即可

//     赋值的时候，要考虑是否收到布局的影响。如oBox.style.left和top赋值前要先把margin值清零

//     ie捕获事件：setCapture()  ie释放事件捕获：releaseCapture()

    </script>

</head>

<body>

<div id="box">

    <h2><a href="javascript:;">点击回放拖动轨迹</a></h2>

    <p><strong>Drag:</strong><span></span></p>

    <p><strong>offsetTop:</strong><span></span></p>

    <p><strong>offsetLeft:</strong><span></span></p>

</div>

</body>

</html>

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