加入“动效”是让用户对应用的行为进行感知的一种有效手段。“列表”是应用中最常使用的一种界面形式,经常会有添加行,删除行,移动行这些操作。设想添加的操作很简单,删除时从大到小,然后消失;添加时从小到大;移动就是先删除再添加。感觉上并不复杂,应该利用CSS的transition就能搞定,可是实际做起来发现有不少问题要处理,下面一一道来。
来些简单的测试
1、最初的版本
<div class='list'> <div class='row-1'>row-1</div> <div class='row-2'>row-2</div></div>
.list{margin:20px;background:#eee;font-size:18px;color:white;}.row-1{background:green;overflow:hidden;padding:15px;}.row-2{background:blue;padding:15px;}/*demo1*/.demo-1 .remove{-webkit-transition: height 3s linear;}.demo-1 .remove.active{height:0;}
var ele = document.querySelector('.demo-1 .row-1');ele.classList.add('remove');ele.classList.add('active');
想法很简单,通过添加“remove”类,设置动画的效果,添加“active”修改css属性,激活动画。
结果和想的不一样,两个问题:1、动画并没有运行;2、row-1并没有消失。为什么?首先,CSS的transition不能作用于auto的属性,因为row-1本来并没有设置height,所以不会产生从现有的高度变到0的动画。第二,height=0只是设置了content区域为0,padding并没有改变,所以还是row-1还是占据了30px的空间。
2、指定固定的height并且padding也加上动画
调整CSS
/*demo2*/.demo-2 .row-1{height:48px;}.demo-2 .remove{-webkit-transition: height 3s linear, padding-top 3s linear;}.demo-2 .row-1.remove.active{height:0;padding-top:0;padding-bottom:0;}
这次的效果是对的,row-1从48px边到0,同时padding也跟着变。
3、还有没有别的办法呢?一定要指定height吗?transform行不行
修改CSS
/*demo3*/.demo-3 .remove{-webkit-transition: -webkit-transform 3s linear,padding 0s linear 3s;}.demo-3 .row-1.remove.active{-webkit-transform-origin:0 0;-webkit-transform:scaleY(0);}
即使没有设置height,通过transform执行动画也是没有问题的。问题是,row-1还在原来的地方,还占着空间,row-2并没有向上挪。由此带来个问题,动画执行完了(包括第2个设置height的例子),row-1并没有删除掉,只是看不见了。
4、解决动画执行完清除元素的问题
修改CSS
.demo-4 .remove{-webkit-transition: height 3s linear, padding 3s linear, opacity 3s linear,color .5s linear;}.demo-4 .row-1.remove.active{padding-top:0;padding-bottom:0;color:rgba(0,0,0,0);opacity:0;}
修改JS
var ele, l;ele = document.querySelector('.demo-4 .row-1');l = ele.addEventListener('webkitTransitionEnd', function(evt){ if (evt.propertyName === 'height') { ele.style.display = 'none'; ele.style.height = ''; ele.removeEventListener('webkitTransitionEnd', l, false); }}, false);ele.style.height = ele.offsetHeight + 'px';ele.classList.add('remove');$timeout(function(){ ele.classList.add('active'); ele.style.height = '0px';});
这次的效果不错。有几个注意的地方:1、通过注册transitionEnd事件可以捕获到动结束;2、可以同时执行多个动效,每个东西结束都会产生transitionEnd事件,通过事件的“propertyName”可以知道是哪个属性的动效结束了。
5、用velocity.js也试了一下
CSS不用设置JS代码
var ele = document.querySelector('.demo-5 .row-1');Velocity(ele, 'slideUp', { duration: 1000 });
看了看执行的过程,也是修改height和padding。但是,velocity用的是requestAnimationFrame函数。我认为如果动效比较简单,就不用引入其他的库了,直接写出来的运行效果差不多。
6、高度搞明白了,变宽度呢?
调整CSS
.demo-6 .row-1{width:100%;}.demo-6 .remove{-webkit-transition: width 3s linear;}.demo-6 .row-1.remove.active{width:0%;}
虽然宽本身可以通过百分比进行设置,但是height不固定的问题还是存在。
7、用上JS解决变width的问题
设置CSS
.demo-7 .row-1{width:100%;height:48px;}.demo-7 .remove{-webkit-transition: width 3s linear, opacity 3s ease;}.demo-7 .row-1.remove.active{width:0%;opacity:0;}
固定了height已有动效正常了。其他的改进可参照前面的例子了。
二、一个完整的例子
完整的例子实在angular中实现的。angular实现首先一个问题就是在什么时机设置动效?因为,angular是双向绑定的,如果在controller中删除了一个对象,渲染界面的时候这个对象就没了,所以必须介入到数据绑定的过程中。angular提供ngAnimatie这个动画模块,试了一下它也确实可以完成ngRepeat列表数据更新的动效。但是要额外引入angular-animation.js,虽然不大,还是觉得不是很有必要。另外,我是在一个已经写好的框架页面上加动画,如果需要引入新的module,需要改框架文件,我觉得不好。试了试动态加载animation模块也没成功,所以就研究了一下自己怎么控制动效。
angular即使不加载animation模块,也有一个$animate,它为动效控制留出了接口。看JS
var fnEnter = $animate.enter, fnLeave = $animate.leave;$animate.enter = function() { var defer = $q.defer(), e = arguments[0], p = arguments[1], a = arguments[2], options = { addClass: 'ng-enter' }; fnEnter.call($animate, e, p, a, options).then(function() { $animate.addClass(e, 'ng-enter-active').then(function(){ var l = e[0].addEventListener('webkitTransitionEnd', function(){ e[0].classList.remove('ng-enter-active'); e[0].classList.remove('ng-enter'); e[0].removeEventListener('webkitTransitionEnd', l, false); defer.resolve(); }, false); }); }); return defer.promise;};$animate.leave = function() { var defer = $q.defer(), e = arguments[0]; $animate.addClass(e, 'ng-leave').then(function(){ $animate.addClass(e, 'ng-leave-active').then(function(){ var l = e[0].addEventListener('webkitTransitionEnd', function(){ fnLeave.call($animate, e).then(function(){ defer.resolve(); }); }, false); }); }); return defer.promise;};
ng-repeat进行数据更新是会调用$animate服务的enters,leave和move方法,所以,要自己控制动效就要重写对应的方法。重写的时候要用$animate添加,直接在dom上设置有问题。(这一段的angular的逻辑比较底层,没有太看明白,还需要深入研究。)
另外,在移动行的位置时,要通过$timeout将删除和插入放到两个digest循环中处理,否则看不出效果。
var index = records.indexOf($scope.selected), r = records.splice(index, 1);$timeout(function(){ records.splice(index + 1, 0, r[0]);},500);
angular的动画和digest循环关系密切,看了angular-animation.js的代码没看明白,还需要深入研究才行。
示例

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