$(".photowall li").css({"position":"absolute"})        /*+++++ 拖曳效果 ++++++         *原理：标记拖曳状态dragging，坐标位置iX、iY         *   mousedown:fn(){dragging = true：记录起始坐标位置，设置鼠标捕获}         *   mouseover:fn(){判断如果dragging = true，则当前坐标位置 - 记录起始坐标位置，绝对定位的元素获得差值}         *   mouseup:fn(){dragging = false：释放鼠标捕获，防止冒泡}         */        var dragging = false;        var iX, iY;        var a;        $(".photowall li").mousedown(function(e) {            dragging = true;            iX = e.clientX - this.offsetLeft;            iY = e.clientY - this.offsetTop;            a=$(this);            var length=$(this).nextAll().length;            for(var i=1;i<=length;i++){                $(this).next().after(this);            }            this.setCapture && this.setCapture();            return false;        });        document.onmousemove = function(e) {            if (dragging) {                var e = e || window.event;                var oX = e.clientX - iX;                var oY = e.clientY - iY;                a.css({"left":oX + "px", "top":oY + "px"});                return false;            }        };        $(document).mouseup(function(e) {            dragging = false;            a[0].releaseCapture();            e.cancelBubble = true;        })