本文介紹原生javascript實作元素拖曳。
思路：
1.先改變被拖曳元素的佈局屬性，關鍵是「position:absolue」；
2.捕捉滑鼠事件"mousedown","mousemove","mouseup"；
3.當觸發"mousedown"時，記錄下當前滑鼠在元素中的相對位置，_x,_y；
4.緊接著處理"mousemove"事件，透過改變元素的top和left屬性來移動元素；
5.當觸發"mouseup"時間時，終止拖曳。
同時，應考慮程式碼的封裝性和瀏覽器的相容性，程式碼如下：
<!DOCTYPE html>
<html>
<head>
<title>draggable div</title>
<style type="text/css">
body{
margin: 0;
padding: 0;
background-color: #fff;
}
#drag_div{
width: 150px;
height: 150px;
padding: 10px;
margin: 10px;
background-color: #66dd33;
cursor: move;
}
</style>
</head>
</html>
<body>
<div id="drag_div"></div>
</body>
<script type="text/javascript">
function Drag () {
this.initialize.apply(this, arguments);
}
Drag.prototype = {
// 初始化
initialize : function (element, options) {
this.element = this.$(element); // 被拖动的对象
this._x = this._y = 0; // 鼠标在元素中的位置
this._moveDrag = this.bind(this, this.moveDrag);
this._stopDrag = this.bind(this, this.stopDrag);
// 设置参数
this.setOptions(options);
// 设置鼠标去“拖”的“柄”对象（注意与被拖动的对象区别）
this.handle = this.$(this.options.handle);
// 设置回调函数
this.onStart = this.options.onStart;
this.onMove = this.options.onMove;
this.onStop = this.options.onStop;
this.handle.style.cursor = "move";
this.changeLayout();
// 注册开始拖动事件
this.addHandler(this.handle, "mousedown", this.bind(this, this.startDrag));
},
// 改变被拖动对象的布局属性
changeLayout: function () {
this.element.style.top = this.element.offsetTop + "px";
this.element.style.left = this.element.offsetLeft + "px";
this.element.style.position = "absolute";
this.element.style.margin = "0";
},
startDrag : function (event) {
var event = event || window.event;
this._x = event.clientX - this.element.offsetLeft;
this._y = event.clientY - this.element.offsetTop;
this.addHandler(document, "mousemove", this._moveDrag);
this.addHandler(document, "mouseup", this._stopDrag);
this.preventDefault(event);
this.handle.setCapture && this.handle.setCapture();
this.onStart();
},
moveDrag : function (event) {
var event = this.getEvent(event);
var iTop = event.clientY - this._y;
var iLeft = event.clientX - this._x;
this.element.style.top = iTop + "px";
this.element.style.left = iLeft + "px";
this.onMove();
},
stopDrag : function () {
this.removeHandler(document, "mousemove", this._moveDrag);
this.removeHandler(document, "mouseup", this._stopDrag);
this.handle.releaseCapture && this.handle.releaseCapture();
this.onStop()
},
setOptions : function (options) {
this.options = {
handle: this.element, //事件对象
onStart : function () {}, // 开始时回调函数
onMove : function(){}, // 拖拽时回调函数
onStop : function(){} // 停止时回调函数
};
for(var p in options){
this.options[p] = options[p];
}
},
$ : function (id) {
return typeof id === "string" ? document.getElementById(id):id;
},
addHandler : function (element, eventType, handler) {
if(element.addEventListener){
return element.addEventListener(eventType, handler, false);
}else{
return element.attachEvent("on"+eventType, handler);
}
},
removeHandler : function (element, eventType, handler) {
if(element.removeEventListener){
return element.removeEventListener(eventType, handler, false);
}else{
return element.detachEvent("on" + eventType, handler);
}
},
getEvent: function (event) {
return event || window.event;
},
preventDefault: function (event) {
if(event.preventDefault){
event.preventDefault();
}else{
event.returnValue = false;
}
},
bind : function (obj, handler) {
return function () {
return handler.apply(obj, arguments);
}
}
};
window.onload = function () {
var drag_div = document.getElementById("drag_div");
var drag = new Drag(drag_div, {handle: drag_div});
}
</script>
</html>
