Question

我已经制作了一个JS对象，有一些原型函数，并且在构造函数中调用它们很好，使用它。[function]

但是在后来的事件处理函数中，这是指元素，而不是对象，我不知道如何解决这个问题：

通过AddListener很好，鼠标按下事件触发，导致enable / disableDragging正常工作。但是在该函数中，“this”是元素，而不是dragger对象，因此我无法调用WindowCenter，DraggingBool或Add / RemoveListener事件。

从阅读起，看起来我可能需要实现prototype.bind？但不确定如何重新安排我现有的代码来执行此操作。或者我是否更改其中一个函数以返回函数？

是的，我知道我可以在jQuery中执行此操作，多次完成，只是试着看看我是否可以使用POJS：）

Dragger = function(element, draggingElement) {
    this.Element = element;
    this.DraggingElement = element;
    this.WindowCenter;
    this.DraggingBool = false;

    this.AddListener(this.DraggingElement, "mousedown", this.enableDragging); 
    this.AddListener(this.DraggingElement, "mouseup", this.disableDragging);
}

Dragger.prototype.AddListener = function (element, eventType, listener, bubble) {
    if (typeof (element) != "object" || typeof (listener) != "function")
        return;
    if (typeof (bubble) == "undefined")
        var bubble = false;
    eventType = eventType.toLowerCase();
    if (eventType.substr(0, 2) == "on")
        eventType = eventType.substr(2);
    if (window.addEventListener) { // Mozilla, Netscape, Firefox
        element.addEventListener(eventType, listener, bubble);
    } else if (window.attachEvent) { // IE
        element.attachEvent("on" + eventType, listener);
    }
}

Dragger.prototype.RemoveListener = function (element, eventType, listener) {
    eventType = eventType.toLowerCase();
    if (eventType.substr(0, 2) == "on")
        eventType = eventType.substr(2);
    if (window.addEventListener) { // Mozilla, Netscape, Firefox
        element.removeEventListener(eventType, listener, false);
    } else if (window.attachEvent) { // IE
        element.detachEvent("on" + eventType, listener);
    }
}

Dragger.prototype.enableDragging = function (e) {
    if (!e) var e = window.event;
    //dont move for right click
    if (e.which && e.which == 3)
        return;
    else if (e.button && e.button == 2)
        return;

    this.DraggingBool = true;
    this.WindowCenter = new Point(e.pageX, e.pageY);
    this.AddListener(document.body, "mouseover", this.mouseMoveListener);
}

Dragger.prototype.disableDragging = function () {
    this.DraggingBool = false;
    this.RemoveListener(document.body, "mouseover", this.mouseMoveListener);
}

Dragger.prototype.mouseMoveListener = function (e) {
    if (!this.DraggingBool)
        return;
    if (!e) var e = window.event;
    e.preventDefault();
    var newLoc = new Point(e.pageX, e.pageY);
    var xDif = windowCenter.X - newLoc.X;
    var yDif = windowCenter.Y - newLoc.Y;
    this.Element.style.left = (this.Element.offsetLeft + xDif) + "px";
    this.Element.style.top = (this.Element.offsetTop + yDif) + "px";
    this.WindowCenter = newLoc;
}

Answer 1

这是因为在使用addEventListener时，执行范围设置为节点，就像您使用了node.onclick = foo一样。在IE中使用attachEvent时，执行范围将成为全局执行范围，即窗口。

解决此问题的一种方法是使用Function.call或Function.apply来指定您喜欢的执行范围。许多库将声明一个绑定函数来帮助解决这个问题，例如：

function bind(fn, context) {
  return function() {
    return fn.apply(context, arguments);
  };
}

this.AddListener(this.DraggingElement, "mousedown",
    bind(this.enableDragging, this));

您还可以向AddListener函数添加上下文参数，并在那里进行绑定。

Ecmascript 5有一个内置绑定方法。

Answer 2

  Function.prototype.bind = function () {
    if (arguments.length < 2 && arguments[0] === undefined) {
     return this;
   }

    var thisObj = this,
    args = Array.prototype.slice.call(arguments),

    obj = args.shift();

    return function () {
     return thisObj.apply(obj, args.concat(Array.prototype.slice.call(arguments)));
    };

  };



  Function.bind = function() {
    var args = Array.prototype.slice.call(arguments);
    return Function.prototype.bind.apply(args.shift(), args);

  }

Dragger = function(element, draggingElement) {
    this.Element = element;
    this.DraggingElement = element;
    this.WindowCenter;
    this.DraggingBool = false;

    this.AddListener(this.DraggingElement, "mousedown", this.enableDragging,this); 
    this.AddListener(this.DraggingElement, "mouseup", this.disableDragging,this);
}

Dragger.prototype.AddListener = function (element, eventType, listener, bubble,dragger_obj) {
    if (typeof (element) != "object" || typeof (listener) != "function")
        return;
    if (typeof (bubble) == "undefined")
        var bubble = false;
    eventType = eventType.toLowerCase();
    if (eventType.substr(0, 2) == "on")
        eventType = eventType.substr(2);
    if (window.addEventListener) { // Mozilla, Netscape, Firefox
        element.addEventListener(eventType, listener.bind(dragger_obj), bubble);
    } else if (window.attachEvent) { // IE
        element.attachEvent("on" + eventType, listener.bind(dragger_obj));
    }
}

Dragger.prototype.RemoveListener = function (element, eventType, listener,dragger_obj) {
    eventType = eventType.toLowerCase();
    if (eventType.substr(0, 2) == "on")
        eventType = eventType.substr(2);
    if (window.addEventListener) { // Mozilla, Netscape, Firefox
        element.removeEventListener(eventType, listener.bind(dragger_obj), false);
    } else if (window.attachEvent) { // IE
        element.detachEvent("on" + eventType, listener.bind(dragger_obj));
    }
}

Dragger.prototype.enableDragging = function (e) {
    if (!e) var e = window.event;
    //dont move for right click
    if (e.which && e.which == 3)
        return;
    else if (e.button && e.button == 2)
        return;

    this.DraggingBool = true;
    this.WindowCenter = new Point(e.pageX, e.pageY);
    this.AddListener(document.body, "mouseover", this.mouseMoveListener,this);
}

Dragger.prototype.disableDragging = function () {
    this.DraggingBool = false;
    this.RemoveListener(document.body, "mouseover", this.mouseMoveListener,this);
}

Dragger.prototype.mouseMoveListener = function (e) {
    if (!this.DraggingBool)
        return;
    if (!e) var e = window.event;
    e.preventDefault();
    var newLoc = new Point(e.pageX, e.pageY);
    var xDif = windowCenter.X - newLoc.X;
    var yDif = windowCenter.Y - newLoc.Y;
    this.Element.style.left = (this.Element.offsetLeft + xDif) + "px";
    this.Element.style.top = (this.Element.offsetTop + yDif) + "px";
    this.WindowCenter = newLoc;
}

无法解析此引用的Javascript对象方法

2 个答案: