没有显示的CSS动画关键帧无法淡入，但不能淡出 [英] CSS animation keyframes with display none works to fade in, but not fade out

问题描述

我有一个在开始时什么都不显示的元素。当我向它添加类时，我希望它使用CSS淡入。

I have an element which has display none on start. When i add a class to it i want it to fade in, using CSS.

我发现本教程使用对淡入效果很好的关键帧。但是，如果我想以相同的方式淡出，该元素将立即隐藏而没有动画。

I found this tutorial to use keyframes which is working nice for fade in. But if i want to fade out the same way, the element gets hidden immediately with no animation.

基本上看起来像这样：

.box {
  display: none;
  opacity: 0;
  animation: FadeOut 1s ease-in-out;

  &.active {
    display: block;
    opacity: 1;
    animation: FadeIn 1s ease-in-out;
  }
}

这里是一个工作示例：
http://codepen.io/MickL/pen/NAopXN

Here is an "working" example: http://codepen.io/MickL/pen/NAopXN

推荐答案

尝试为 display：none 设置动画是问题的根源。为什么使用淡入和淡出的困惑不是来自同时使用 display 和 opacity 。

Trying to animate the display:none is the root of your problem. The confusion for why the fade-in works and the fade-out doesn't comes from the combination of using both display and opacity.

显示属性仅由 .active 已应用；动画实际上并没有改变它，而 opacity 却按预期进行了动画处理。在淡入时，这意味着您立即显示元素，然后从透明过渡到不透明。在淡出时，这意味着您可以立即隐藏元素，然后在隐藏时从不透明过渡到透明。

The display property is only being dictated by whether .active is applied; the animations aren't actually changing it, whereas the opacity is animated as expected. On the fade-in, this means that you immediately show your element, which then transitions from transparent to opaque. On the fade-out, this means that you immediately hide your element, which then transitions from opaque to transparent while hidden.

有两种方法可以解决此问题，但它取决于上下文。例如，您可以将其保留为 block 元素，并使用 height 属性使其折叠：

There are a couple different ways you could solve this, but it sort of depends on the context. For example, you could leave it as a block element and use the height property to make it collapse:

$('button').on('click', function(e) {
  e.preventDefault();
  $(this).siblings('.box').toggleClass('active');
})

@import "bourbon";
 * {
  box-sizing: border-box;
  text-align: center;
}
button {
  margin: 30px 0;
  border: 1px solid #ccc;
  text-align: center;
  padding: 1em;
  background: none;
  box-shadow: none;
}
.box {
  margin: 0 auto;
  width: 80%;
  height: 0;
  display: block;
  line-height: 100px;
  background: #ccc;
  border: 1px solid #444;
  text-align: center;
  opacity: 0;
  animation: FadeOut 1s ease-in-out;
}
.box.active {
  display: block;
  height: initial;
  opacity: 1;
  animation: FadeIn 1s ease-in-out;
}
@keyframes FadeIn {
  0% {
    opacity: 0;
    height: initial;
  }
  100% {
    opacity: 1;
    height: initial;
  }
}
@keyframes FadeOut {
  0% {
    opacity: 1;
    height: initial;
  }
  99% {
    opacity: 0;
    height: initial;
  }
  100% {
    height: 0;
    opacity: 0;
    height: 0;
  }
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="col">
  <button class="toggle-good">Toggle display</button>
  <p class="box good">I move nicely!</p>
  <p>Extra paragraph to show collapse</p>
</div>

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