【小贴士】关于transitionEnd/animate的一个有趣故事

前言

在很久之前，我们项目有一个动画功能，功能本身很简单，便是典型的右进左出，并且带动画功能

以当时来说，虽然很简单，但是受限于框架本身的难度，就直接使用了CSS3的方式完成了功能

当时主要使用transform与animation实现功能，并且用了一个settimeout执行回调，然后此事便不了了之了

但是出来混总是要还的，这不，最近相似的东西又提了出来，我们当然可以将原来的那套东西拿来用，但是看着那个settimeout总是不是滋味，因为这样捕捉回调的效果以及可能引起的BUG大家都懂，于是就想使用transitionEnd监控动画结束再执行相关回调，于是便有了一个有趣的想法

当时的心声

嗯，不行，这次我要写一个通用的东西，他至少有这些功能：

① 我可以给他一个CSS变化属性

② 我可以给他一个时间长度

③ 我可以给他一个动画曲线参数

有了以上东西我就可以让一个元素触发动画，并且对其注册transitionEnd事件，最后执行我们的回调，于是我基本就陷进去了

但是，我想着想着突然感觉不对，感觉以上东西好像在哪里见过，于是一个叫animate的东西冒了出来

突然一刹那，我有一个不妙的感觉，搞出来一看：

animate
animate(properties, [duration, [easing, [function(){ ... }]]])   ⇒ self
      animate(properties, { duration: msec, easing: type, complete: fn })   ⇒ self
      animate(animationName, { ... })   ⇒ self
  
对当前Zepto集合对象中元素进行css transition属性平滑过渡。

properties: 一个对象，该对象包含了css动画的值，或者css帧动画的名称。
duration (默认 400)：以毫秒为单位的时间，或者一个字符串。
fast (200 ms)
slow (600 ms)
任何$.fx.speeds自定义属性
easing (默认 linear)：指定动画的缓动类型，使用以下一个：
ease
linear
ease-in / ease-out
ease-in-out
cubic-bezier(...)
complete：动画完成时的回调函数

于是，我自己的想法就只能呵呵了，这个就是我要的嘛......

而且zepto里面便是监听transitionEnd这个事件触发回调，所以，我们今天就来学习这个animate即可！！！

transitionEnd

transitionEnd是CSS3动画transition唯一的事件，我之前还去找个transitionStart，米有找到......

介绍他之前，我们先来个简单的例子，W3C上面的例子：

<!DOCTYPE html>
<html>
<head>
    <style>
        div { width: 100px; height: 100px; background: blue; transition: width 2s; -moz-transition: width 2s; /* Firefox 4 */ -webkit-transition: width 2s; /* Safari and Chrome */ -o-transition: width 2s; /* Opera */ }
        
        div:hover { width: 300px; }
    </style>
</head>
<body>
    <div>
    </div>
    <p>
        请把鼠标指针移动到蓝色的 div 元素上，就可以看到过渡效果。</p>
    <p>
        <b>注释：</b>本例在 Internet Explorer 中无效。</p>
</body>
</html>

好了，现在若是我们要在动画结束时候加一个事件该怎么办呢？ 

<!DOCTYPE html>
<html>
<head>
    <style>
        div { width: 100px; height: 100px; background: blue; transition: width 1s; -moz-transition: width 1s; /* Firefox 4 */ -webkit-transition: width 1s; /* Safari and Chrome */ -o-transition: width 1s; /* Opera */ }
        
        div:hover { width: 300px; }
    </style>
</head>
<body>
    <div id="demo">
    </div>
    <br />
    <span id="msg"></span>
    <p>
        请把鼠标指针移动到蓝色的 div 元素上，就可以看到过渡效果。</p>
    <p>
        <b>注释：</b>本例在 Internet Explorer 中无效。</p>
    <script type="text/javascript">
        var demo = document.getElementById('demo');
        var msg = document.getElementById('msg');

//        eventType(this.scroller, 'transitionend', this);
//        eventType(this.scroller, 'webkitTransitionEnd', this);
//        eventType(this.scroller, 'oTransitionEnd', this);
//        eventType(this.scroller, 'MSTransitionEnd', this);

        demo.addEventListener('webkitTransitionEnd', function () {
            msg.innerHTML = '事件回调，当前原始宽度：' + window.getComputedStyle(demo).width;
        });
        
    </script>
</body>
</html>

这个例子虽然简单却很好的说明了一些问题，现在我们就来简单模拟一下animate

简单模拟animate

既然zepto已经很好的实现了该功能，我们这里就简单的模拟下即可，然后看看zepto源码

var demo = document.getElementById('demo');
var msg = document.getElementById('msg');

//简单模拟animate，参数问题就不管他了，暂时只考虑width吧
function animate(el, css, time, fn) {
      
  if (!el) return;

  var callback = function () {
    fn(arguments);
    el.removeEventListener('webkitTransitionEnd', callback);
  };

  el.addEventListener('webkitTransitionEnd', callback);

  for (var k in css) {
    //这里暂时只考虑webkit内核
    el.style['-webkit-transition'] = k + ' ' + time + 's';
  }

  for (var k in css) {
    //这里暂时只考虑webkit内核
    el.style[k] = css[k];
  }
}

demo.addEventListener('mouseenter', function () {
  animate(demo, { width: '300px' }, 1, fn);
});

demo.addEventListener('mouseout', function () {
  animate(demo, { width: '100px' }, 2, fn);
});

var fn = function () {
  msg.innerHTML = '事件回调，当前原始宽度：' + window.getComputedStyle(demo).width;
}

这是一个简单的实现，每次执行animate的时候，先会执行一次transitionEnd的事件注册，并且执行一次后就销毁

第二步为其设置transition属性，如果可以的话，这里最好是可以消除

最后一步就是为其设置css属性即可整个逻辑很简单，大概原理就是这样，我接下来来看看zepto高大上的实现！！！

zepto高大上的animate

zepto要实现以上代码的话，这样搞：

var demo = $('#demo');
var msg = $('#msg');

var fn = function () {
  msg.html('事件回调，当前原始宽度：' + demo.width());
};

demo.on('mouseenter', function () {
  demo.animate({ 'width': '300px' }, 1000, 'ease-out', fn);
});

demo.on('mouseout', function () {
  demo.animate({ 'width': '100px' }, 2000, 'ease-out', fn);
});

然后我们现在来看看源码：

;(function($, undefined){
  var prefix = '', eventPrefix, endEventName, endAnimationName,
    vendors = { Webkit: 'webkit', Moz: '', O: 'o' },
    document = window.document, testEl = document.createElement('div'),
    supportedTransforms = /^((translate|rotate|scale)(X|Y|Z|3d)?|matrix(3d)?|perspective|skew(X|Y)?)$/i,
    transform,
    transitionProperty, transitionDuration, transitionTiming, transitionDelay,
    animationName, animationDuration, animationTiming, animationDelay,
    cssReset = {}

  function dasherize(str) { return str.replace(/([a-z])([A-Z])/, '$1-$2').toLowerCase() }
  function normalizeEvent(name) { return eventPrefix ? eventPrefix + name : name.toLowerCase() }

  $.each(vendors, function(vendor, event){
    if (testEl.style[vendor + 'TransitionProperty'] !== undefined) {
      prefix = '-' + vendor.toLowerCase() + '-'
      eventPrefix = event
      return false
    }
  })

  transform = prefix + 'transform'
  cssReset[transitionProperty = prefix + 'transition-property'] =
  cssReset[transitionDuration = prefix + 'transition-duration'] =
  cssReset[transitionDelay    = prefix + 'transition-delay'] =
  cssReset[transitionTiming   = prefix + 'transition-timing-function'] =
  cssReset[animationName      = prefix + 'animation-name'] =
  cssReset[animationDuration  = prefix + 'animation-duration'] =
  cssReset[animationDelay     = prefix + 'animation-delay'] =
  cssReset[animationTiming    = prefix + 'animation-timing-function'] = ''

  $.fx = {
    off: (eventPrefix === undefined && testEl.style.transitionProperty === undefined),
    speeds: { _default: 400, fast: 200, slow: 600 },
    cssPrefix: prefix,
    transitionEnd: normalizeEvent('TransitionEnd'),
    animationEnd: normalizeEvent('AnimationEnd')
  }

  $.fn.animate = function(properties, duration, ease, callback, delay){
    if ($.isFunction(duration))
      callback = duration, ease = undefined, duration = undefined
    if ($.isFunction(ease))
      callback = ease, ease = undefined
    if ($.isPlainObject(duration))
      ease = duration.easing, callback = duration.complete, delay = duration.delay, duration = duration.duration
    if (duration) duration = (typeof duration == 'number' ? duration :
                    ($.fx.speeds[duration] || $.fx.speeds._default)) / 1000
    if (delay) delay = parseFloat(delay) / 1000
    return this.anim(properties, duration, ease, callback, delay)
  }

  $.fn.anim = function(properties, duration, ease, callback, delay){
    var key, cssValues = {}, cssProperties, transforms = '',
        that = this, wrappedCallback, endEvent = $.fx.transitionEnd,
        fired = false

    if (duration === undefined) duration = $.fx.speeds._default / 1000
    if (delay === undefined) delay = 0
    if ($.fx.off) duration = 0

    if (typeof properties == 'string') {
      // keyframe animation
      cssValues[animationName] = properties
      cssValues[animationDuration] = duration + 's'
      cssValues[animationDelay] = delay + 's'
      cssValues[animationTiming] = (ease || 'linear')
      endEvent = $.fx.animationEnd
    } else {
      cssProperties = []
      // CSS transitions
      for (key in properties)
        if (supportedTransforms.test(key)) transforms += key + '(' + properties[key] + ') '
        else cssValues[key] = properties[key], cssProperties.push(dasherize(key))

      if (transforms) cssValues[transform] = transforms, cssProperties.push(transform)
      if (duration > 0 && typeof properties === 'object') {
        cssValues[transitionProperty] = cssProperties.join(', ')
        cssValues[transitionDuration] = duration + 's'
        cssValues[transitionDelay] = delay + 's'
        cssValues[transitionTiming] = (ease || 'linear')
      }
    }

    wrappedCallback = function(event){
      if (typeof event !== 'undefined') {
        if (event.target !== event.currentTarget) return // makes sure the event didn't bubble from "below"
        $(event.target).unbind(endEvent, wrappedCallback)
      } else
        $(this).unbind(endEvent, wrappedCallback) // triggered by setTimeout

      fired = true
      $(this).css(cssReset)
      callback && callback.call(this)
    }
    if (duration > 0){
      this.bind(endEvent, wrappedCallback)
      // transitionEnd is not always firing on older Android phones
      // so make sure it gets fired
      setTimeout(function(){
        if (fired) return
        wrappedCallback.call(that)
      }, (duration * 1000) + 25)
    }

    // trigger page reflow so new elements can animate
    this.size() && this.get(0).clientLeft

    this.css(cssValues)

    if (duration <= 0) setTimeout(function() {
      that.each(function(){ wrappedCallback.call(this) })
    }, 0)

    return this
  }

  testEl = null
})(Zepto)
View Code

看代码首先还是看入口，我们这里的入口就是animate

demo.animate({ 'width': '300px' }, 1000, 'ease-out', fn);
 1 $.fn.animate = function(properties, duration, ease, callback, delay){
 2   if ($.isFunction(duration))
 3     callback = duration, ease = undefined, duration = undefined
 4   if ($.isFunction(ease))
 5     callback = ease, ease = undefined
 6   if ($.isPlainObject(duration))
 7     ease = duration.easing, callback = duration.complete, delay = duration.delay, duration = duration.duration
 8   if (duration) duration = (typeof duration == 'number' ? duration :
 9                   ($.fx.speeds[duration] || $.fx.speeds._default)) / 1000
10   if (delay) delay = parseFloat(delay) / 1000
11   return this.anim(properties, duration, ease, callback, delay)
12 }

他首先这里做了一些默认处理，因为我们传递的参数是不定的，所以第二个参数极有可能是回调

所以他第一句就是做一个简单的判断，第二句也不例外

其实他整个animate都是做一些属性处理，并未做实际的事情，具体的实现还是在anim中

 1 $.fn.anim = function(properties, duration, ease, callback, delay){
 2   var key, cssValues = {}, cssProperties, transforms = '',
 3       that = this, wrappedCallback, endEvent = $.fx.transitionEnd,
 4       fired = false
 5 
 6   if (duration === undefined) duration = $.fx.speeds._default / 1000
 7   if (delay === undefined) delay = 0
 8   if ($.fx.off) duration = 0
 9 
10   if (typeof properties == 'string') {
11     // keyframe animation
12     cssValues[animationName] = properties
13     cssValues[animationDuration] = duration + 's'
14     cssValues[animationDelay] = delay + 's'
15     cssValues[animationTiming] = (ease || 'linear')
16     endEvent = $.fx.animationEnd
17   } else {
18     cssProperties = []
19     // CSS transitions
20     for (key in properties)
21       if (supportedTransforms.test(key)) transforms += key + '(' + properties[key] + ') '
22       else cssValues[key] = properties[key], cssProperties.push(dasherize(key))
23 
24     if (transforms) cssValues[transform] = transforms, cssProperties.push(transform)
25     if (duration > 0 && typeof properties === 'object') {
26       cssValues[transitionProperty] = cssProperties.join(', ')
27       cssValues[transitionDuration] = duration + 's'
28       cssValues[transitionDelay] = delay + 's'
29       cssValues[transitionTiming] = (ease || 'linear')
30     }
31   }
32 
33   wrappedCallback = function(event){
34     if (typeof event !== 'undefined') {
35       if (event.target !== event.currentTarget) return // makes sure the event didn't bubble from "below"
36       $(event.target).unbind(endEvent, wrappedCallback)
37     } else
38       $(this).unbind(endEvent, wrappedCallback) // triggered by setTimeout
39 
40     fired = true
41     $(this).css(cssReset)
42     callback && callback.call(this)
43   }
44   if (duration > 0){
45     this.bind(endEvent, wrappedCallback)
46     // transitionEnd is not always firing on older Android phones
47     // so make sure it gets fired
48     setTimeout(function(){
49       if (fired) return
50       wrappedCallback.call(that)
51     }, (duration * 1000) + 25)
52   }
53 
54   // trigger page reflow so new elements can animate
55   this.size() && this.get(0).clientLeft
56 
57   this.css(cssValues)
58 
59   if (duration <= 0) setTimeout(function() {
60     that.each(function(){ wrappedCallback.call(this) })
61   }, 0)
62 
63   return this
64 }

传入anim的参数真的就没有什么问题了

第一个是css属性

第二个是动画运行时间

第三个是动画曲线，这个很神奇，没事不要去搞他

第四个是回调函数

第五个是什么就暂时不知道是什么了

进入后，10行之前还是在做容错性处理，这里我们最主要关注点放在endEvent上面

这个东西由前面的fx对象获取：

$.fx = {
  off: (eventPrefix === undefined && testEl.style.transitionProperty === undefined),
  speeds: { _default: 400, fast: 200, slow: 600 },
  cssPrefix: prefix,
  transitionEnd: normalizeEvent('TransitionEnd'),
  animationEnd: normalizeEvent('AnimationEnd')
}

而我们要做的chrome、firefox等兼容全部被normalizeEvent做了，这里

vendors = { Webkit: 'webkit', Moz: '', O: 'o' }
testEl = document.createElement('div')
$.each(vendors, function(vendor, event){
  if (testEl.style[vendor + 'TransitionProperty'] !== undefined) {
    prefix = '-' + vendor.toLowerCase() + '-'
    eventPrefix = event
    return false
  }
})

这里根据这种方式得出了兼容事件的前缀，webkit的话会返回webkit前缀：

$.fx.transitionEnd => "webkitTransitionEnd"

然后下一步简单仍然是先设置transition相关的属性，并且指定事件结束事件回调：

cssValues[animationName] = properties
cssValues[animationDuration] = duration + 's'
cssValues[animationDelay] = delay + 's'
cssValues[animationTiming] = (ease || 'linear')
endEvent = $.fx.animationEnd

当然，如果我们传入的CSS不止一个的话，下面的处理会相对复杂点

cssProperties = []
// CSS transitions
for (key in properties)
  if (supportedTransforms.test(key)) transforms += key + '(' + properties[key] + ') '
  else cssValues[key] = properties[key], cssProperties.push(dasherize(key))

if (transforms) cssValues[transform] = transforms, cssProperties.push(transform)
if (duration > 0 && typeof properties === 'object') {
  cssValues[transitionProperty] = cssProperties.join(', ')
  cssValues[transitionDuration] = duration + 's'
  cssValues[transitionDelay] = delay + 's'
  cssValues[transitionTiming] = (ease || 'linear')
}

这里先放下处理Transform等新属性之外，与上面的操作无他

然后关键步骤又来了，

 1 wrappedCallback = function(event){
 2   if (typeof event !== 'undefined') {
 3     if (event.target !== event.currentTarget) return // makes sure the event didn't bubble from "below"
 4     $(event.target).unbind(endEvent, wrappedCallback)
 5   } else
 6     $(this).unbind(endEvent, wrappedCallback) // triggered by setTimeout
 7 
 8   fired = true
 9   $(this).css(cssReset)
10   callback && callback.call(this)
11 }
12 if (duration > 0){
13   this.bind(endEvent, wrappedCallback)
14   // transitionEnd is not always firing on older Android phones
15   // so make sure it gets fired
16   setTimeout(function(){
17     if (fired) return
18     wrappedCallback.call(that)
19   }, (duration * 1000) + 25)
20 }

他这里首先声明了回调函数wrappedCallback，这个函数首先干的事情是注销事件

然后执行传入的回调，这里将this指向了调用者，也就是绑定的标签

后面便是真实的事件绑定操作，里面仍然有一个延时函数执行

其中有一个状态机fired，来记录该事件是否触发

然后就为css复制了，这个时候动画执行结束便会触发transitionEnd事件了

最后，代码结束.......

结语

今天，我们简单的说了下zepto的animate方法，希望对各位有帮助，若是文中有任何问题请提出

posted on 2014-03-15 22:40  叶小钗  阅读(9511)  评论(5)  编辑  收藏  举报

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