javascript简单拖拽鼠标事件mousedown和mousemove以及mouseup实例分析

简单拖拽实现

javascript简单拖拽鼠标事件mousedown和mousemove以及mouseup实例分析-LMLPHP

mousedown 的时候创建拖动对象，mouseup的时候释放对象，原理弄清楚了其实很简单。

简单拖拽实现代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>简单拖拽实现</title>
<style type="text/css">
*{margin:0;padding:0;}
#box{ margin:20px auto; position:relative; width:400px; height:400px; background:#ccc; border:1px solid #333; postion:relative; }
#dragBox{ width:50px; height:50px;  text-align:center; line-height: 50px;position: absolute; background:blue; cursor:move; font-size:12px; color:#fff;}
</style> 
</head>
<body>
<div id="box">
        <div id="dragBox">拖我</div>
</div>
<script type="text/javascript">
var VVG = {};  //命名空间
VVG.DOM = {
    $: function(id) { //创建方便的选择符
        return typeof id == "string" ? document.getElementById(id) : id;
    },
    bindEvent: function(node, type, func) { //事件绑定方法
        if (node.addEventListener) {
            node.addEventListener(type, func, false);
        } else if (node.attachEvent) {
            node.attachEvent("on" + type, func);
        } else {
            node["on" + type] = func;
        }
    },
    getEvent: function(event) { //获取事件
        return event ? event : window.event;
    },
    getTarget: function(event) { //获取事件目标
        return event.target || event.srcElement;
    }
}
    var DragDrop =  function() { //新建一个返回对象的函数
        var box = VVG.DOM.$("box"); //获取外围BOX
        var dragBox = VVG.DOM.$("dragBox");//获取需要拖动的BOX
        var dragging = null; //初始化对象
        function drag(event) { //事件执行函数
            event = VVG.DOM.getEvent(event); 
            var target = VVG.DOM.getTarget(event);
            switch (event.type) {//判断事件类型
            case "mousedown":
                if(target.id == "dragBox"){ //当事件对象的ID等于要拖动的BOX的ID时
                    dragging = target; //赋值到拖动目标
                }
                break;
            case "mousemove":
                if(dragging){ //当有拖动目标时执行
                    sTop = document.documentElement.scrollTop || document.body.scrollTop; //当有滚动条的时候卷去页面的高度
                    dragging.style.left = (event.clientX - box.offsetLeft - dragBox.offsetWidth/2) + "px";
                    dragging.style.top = (event.clientY + sTop - box.offsetTop  - dragBox.offsetHeight/2 ) + "px";
                    var left = parseInt(dragging.style.left);
                    var top = parseInt(dragging.style.top);
                    //console.log("left:"+left+"-----top:"+top + "-------sTop:"+sTop);
                    // 比较坐标是否超出外围的BOX
                    if(left < 0){
                        dragging.style.left = 0 +"px";
                    }
                    if(top < 0){
                        dragging.style.top = 0+"px";
                    }
                    if(left > box.offsetWidth - dragBox.offsetWidth){
                        dragging.style.left = (box.offsetWidth - dragBox.offsetWidth - 2 )+"px";
                    }
                    if(top >  box.offsetHeight - dragBox.offsetHeight){
                        dragging.style.top =( box.offsetHeight - dragBox.offsetHeight  - 2 )+"px";
                    }
                }
                break;
            case "mouseup":
                // 清空拖动目标
                dragging = null;
                break;
            }
        };
        return {
            dragStart: function() {
                // 绑定事件
                VVG.DOM.bindEvent(document, "mousedown", drag);
                VVG.DOM.bindEvent(document, "mousemove", drag);
                VVG.DOM.bindEvent(document, "mouseup", drag);
            }
        }
    }();
    DragDrop.dragStart();
</script>
</body>
</html>

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