Javascript教程:网页拖放实现代码(三)
添加自定义事件
拖放功能还不能真正的应用起来,除非能知道什么时候拖放开始了。从这点上看,前面的代码没有提供任何方法表示拖动开始、正在拖动或者已经结束。这时,可以使用自定义事件来指示这几个事件的发生,让应用的其它部分与拖动功能进行交互。
由于DragDrop对象是一个使用了模块模式的单例,所以需要进行一些更改来使用EventTarget类型。首先,创建一个新的EventTarget对象,然后添加enable()和disable()方法,最后返回这个对象。看一下内容:
这段代码定义了3个事件:dragstart、drag和dragend。它们都将被拖动的元素设置为了target,并给出了x和y属性来表示当前的位置。
它们触发于dragdrop对象上,之后在返回对象前给对象增加enable()和disable()方法。这些模块模式中的细小更改令DragDrop对象支持了事件,如下:
var EventUtil = {
getEvent: function (event) {
return event ? event : window.event;
},
getTarget: function (event) {
return event.target || event.srcElement;
},
addHandler: function (element, type, handler) {
if (element.addEventListener) {
element.addEventListener(type, handler, false);
} else if (element.attachEvent) {
element.attachEvent("on" + type, handler);
} else {
element["on" + type] = handler;
}
},
removeHandler: function (element, type, handler) {
if (element.removeEventListener) {
element.removeEventListener(type, handler, false);
} else if (element.detachEvent) {
element.detachEvent("on" + type, handler);
} else {
element["on" + type] = null;
}
}
};
function EventTarget() {
this.handlers = {};
}
EventTarget.prototype = {
constructor: EventTarget,
addHandler: function (type, handler) {
if (typeof this.handlers[type] == "undefined") {
this.handlers[type] = [];
}
this.handlers[type].push(handler);
},
fire: function (event) {
if (!event.target) {
event.target = this;
}
if (this.handlers[event.type] instanceof Array) {
var handlers = this.handlers[event.type];
for (var i = 0, len = handlers.length; i < len; i++) {
handlers[i](event);
}
}
},
removeHandler: function (type, handler) {
if (this.handlers[type] instanceof Array) {
var handlers = this.handlers[type];
for (var i = 0, len = handlers.length; i < len; i++) {
if (handlers[i] === handler) {
break;
}
}
handlers.splice(i, 1);
}
}
};
var DragDrop = function () {
var dragdrop = new EventTarget();
var dragging = null;
var diffX = 0;
var diffY = 0;
function handleEvent(event) {
//获取事件和目标
event = EventUtil.getEvent(event);
var target = EventUtil.getTarget(event);
//确定事件类型
switch (event.type) {
case "mousedown":
if (target.className.indexOf("draggable") > -1) {
dragging = target;
diffX = event.clientX - target.offsetLeft;
diffY = event.clientY - target.offsetTop;
dragdrop.fire({
type: "dragstart",
target: dragging,
x: event.clientX,
y: event.clientY
});
}
break;
case "mousemove":
if (dragging !== null) {
//获取事件
event = EventUtil.getEvent(event);
//指定位置
dragging.style.left = (event.clientX - diffX) + "px";
dragging.style.top = (event.clientY - diffY) + "px";
//触发自定义事件
dragdrop.fire({
type: "drag",
target: dragging,
x: event.clientX,
y: event.clientY
});
}
break;
case "mouseup":
dragdrop.fire({
type: "dragend",
target: dragging,
x: event.clientX,
y: event.clientY
});
dragging = null;
break;
}
};
//公共接口
dragdrop.enable = function () {
EventUtil.addHandler(document, "mousedown", handleEvent);
EventUtil.addHandler(document, "mousemove", handleEvent);
EventUtil.addHandler(document, "mouseup", handleEvent);
};
dragdrop.disabled = function () {
EventUtil.removeHandler(document, "mousedown", handleEvent);
EventUtil.removeHandler(document, "mousemove", handleEvent);
EventUtil.removeHandler(document, "mouseup", handleEvent);
}
return dragdrop;
}();
//启用拖放
DragDrop.enable();
DragDrop.addHandler("dragstart", function (event) {
var status = document.getElementById("status");
status.innerHTML = "Started dragging " + event.target.id;
});
DragDrop.addHandler("drag", function (event) {
var status = document.getElementById("status");
status.innerHTML += "<br />Dragged " + event.target.id + " to (" + event.x + "," + event.y + ")";
});
DragDrop.addHandler("dragend", function (event) {
var status = document.getElementById("status");
status.innerHTML += "<br />Dragged " + event.target.id + " at (" + event.x + "," + event.y + ")";
});
这里,为DragDrop对象每个事件添加了事件处理程序。还是用了一个元素来实现被拖动的元素当前的状态和位置。一旦元素被放下了,就可以看到从它一开始被拖动之后经过的所有的中间步骤。
为DragDrop添加自定义事件可以使这个对象更健壮,它将可以在网络应用中处理复杂的拖放功能。