使用自定义事件封装拖拽事件
首先需要用到两个之前定义的工具类，主要是为了兼容IE。这里只用到了其中的 addHandler 和 removeHandler 方法，不使用这个类而用原生的事件注册也是可以的。
EventUtil.js1
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82var EventUtil = {
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.addEventListener) {
element.removeEventListener(type, handler, false);
} else if (element.attachEvent) {
element.detachEvent("on" + type, handler);
} else {
element["on" + type] = null;
}
},
getEvent: function (event) {
return event ? event : window.event;
},
getTarget: function (event) {
return event.targrt || event.srcElement;
},
preventDefault: function (event) {
if (event.preventDefault) {
event.preventDefault();
} else {
event.returnValue = false;
}
},
stopPropagation: function (event) {
if (event.stopPropagation) {
event.stopPropagation();
} else {
event.cancelable = true;
}
},
getRelatedTarget: function (event) {
if (event.relatedTarget) {
return event.relatedTarget;
} else if (event.toElement) {
return event.toElement;
} else if (event.fromElement) {
return event.fromElement;
}
},
getButton: function (event) {
if (document.implementation.hasFeature("MouseEvents", "2.0")) {
return event.button;
} else {
switch (event.button) {
case 0:
case 1:
case 3:
case 5:
case 7:
return 0;
case 2:
case 6:
return 2;
case 4:
return 1;
}
}
},
getWheelDelta: function (event) {
if (event.wheelDelta) {
return (client.engine.opera && client.engine.opera < 9.5 ? -event.wheelDelta : event.wheelDelta);
} else {
return -event.detail * 40;
}
},
getCharCode: function (event) {
if (typeof event.charCode == "number") {
return event.charCode;
} else {
return event.keyCode;
}
}
};
EventTarget.js1
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36//自定义事件
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[event.type] instanceof Array) {
var handlers = this.handlers[event.type];
for (var i = 0, len = handlers.length; i < len; i++) {
if (handlers[i] === handler) {
break;
}
}
handlers.splice(i, 1);
}
}
};
这是一个自定义事件的封装类，定义了事件的 addHandler,fire,removeHandler 方法。
接下来设计一个名为DragDrop的单例1
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57var DragDrop = (function () {
var dragdrop = new EventTarget(),
dragging = null,
diffX = 0,
diffY = 0;
function handleEvent (event) {
event = EventUtil.getEvent(event);
var target = EventUtil.getTarget(event);
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) {
dragging.style.left = (event.clientX - diffX) + "px";
dragging.style.top = (event.clientY - diffY) + "px";
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;
}
}
dragdrop.enable = function () {
EventUtil.addHandler(document, "mousedown", handleEvent);
EventUtil.addHandler(document, "mousemove", handleEvent);
EventUtil.addHandler(document, "mouseup", handleEvent);
};
dragdrop.disable = function () {
EventUtil.removeHandler(document, "mousedown", handleEvent);
EventUtil.removeHandler(document, "mousemove", handleEvent);
EventUtil.removeHandler(document, "mouseup", handleEvent);
};
return dragdrop;
})();
DragDrop 返回一个 EventTarget 类的实例对象，并添加了 enable 和 disable 两个方法用于开启/关闭拖拽事件的监听。
使用时给想要拖拽的元素加上『dragable』类名，再调用 DragDrop.enable 方法。1
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13DragDrop.enable();
DragDrop.addHandler("dragstart", function () {
var status = document.getElementById("status");
status.innerHTML = "Started dragging " + event.target.id;
});
DragDrop.addHandler("drag", function () {
var status = document.getElementById("status");
status.innerHTML = "Dragged " + event.target.id + " to (" + event.x + ", " + event.y + ")";
});
DragDrop.addHandler("dragend", function () {
var status = document.getElementById("status");
status.innerHTML = "Dropped " + event.target.id + " st (" + event.x + ", " + event.y + ")";
});
这样的封装使得拖拽可以更好的复用，不必再对每个拖拽的元素进行处理，省略了大量的逻辑操作，api设计也和原生没有什么区别，非常易用，这样的处理是非常值得的。