How to prevent css keyframe animation to run on pa

问题:

I have a div in which I animate the content:

#container {
  position: relative;
  width: 100px;
  height: 100px;
  border-style: inset;
}
#content {
  visibility: hidden;
  -webkit-animation: animDown 1s ease;
  position: absolute;
  top: 100px;
  width: 100%;
  height: 100%;
  background-color: lightgreen;
}
#container:hover #content {
  -webkit-animation: animUp 1s ease;
  animation-fill-mode: forwards;
  -webkit-animation-fill-mode: forwards;
}
@-webkit-keyframes animUp {
  0% {
    -webkit-transform: translateY(0);
    visibility: hidden;
    opacity: 0;
  }
  100% {
    -webkit-transform: translateY(-100%);
    visibility: visible;
    opacity: 1;
  }
}
@-webkit-keyframes animDown {
  0% {
    -webkit-transform: translateY(-100%);
    visibility: visible;
    opacity: 1;
  }
  100% {
    -webkit-transform: translateY(0);
    visibility: hidden;
    opacity: 0;
  }
}

<div id="container">
  <div id="content"></div>
</div>

On hover content slides into the container div. My problem is, when I refresh the page, and the page loads the #content's animDown animation will run, and I'd prefer it to run only after a hover event.

Is there a way to do this pure CSS, or I have to figure something out in JS?

http://jsfiddle.net/d0yhve8y/

回答1:

Solution 1 - Add down animation on first hover

Probably the best option is to not put the down animation on until the user has hovered over the container for the first time.

This involves listening to the mouseover event then adding a class with the animation at that point, and removing the event listener. The main (potential) downside of this is it relies on Javascript.

;(function(){
    var c = document.getElementById('container');
    function addAnim() {
        c.classList.add('animated')
        // remove the listener, no longer needed
        c.removeEventListener('mouseover', addAnim);
    };

    // listen to mouseover for the container
    c.addEventListener('mouseover', addAnim);
})();

#container {
    position:relative;
    width:100px;
    height:100px;
    border-style:inset;
}
#content {
    position:absolute;
    top:100px;
    width:100%;
    height:100%;
    background-color:lightgreen;
    opacity:0;
}

/* This gets added on first mouseover */
#container.animated #content {
    -webkit-animation:animDown 1s ease;
}

#container:hover #content {
    -webkit-animation:animUp 1s ease;
    animation-fill-mode:forwards;
    -webkit-animation-fill-mode:forwards;
}

@-webkit-keyframes animUp {
    0% {
        -webkit-transform:translateY(0);
        opacity:0;
    }
    100% {
        -webkit-transform:translateY(-100%);
        opacity:1;
    }
}
@-webkit-keyframes animDown {
    0% {
        -webkit-transform:translateY(-100%);
        opacity:1;
    }
    100% {
        -webkit-transform:translateY(0);
        opacity:0;
    }
}

<div id="container">
    <div id="content"></div>
</div>

Solution 2 - play animation hidden

Another way around this is to initially hide the element, make sure the animation plays while it is hidden, then make it visible. The downside of this is that the timing could be slightly off and it is made visible too early, and also the hover isn't available straight away.

This requires some Javascript which waits for the length of the animation and only then makes #content visible. This means you also need to set the initial opacity to 0 so it doesn't appear on load and also remove the visibility from the keyframes - these aren't doing anything anyway:

// wait for the animation length, plus a bit, then make the element visible
window.setTimeout(function() {
    document.getElementById('content').style.visibility = 'visible';
}, 1100);

#container {
    position:relative;
    width:100px;
    height:100px;
    border-style:inset;
}

#content {
    visibility:hidden;
    -webkit-animation:animDown 1s ease;
    position:absolute;
    top:100px;
    width:100%;
    height:100%;
    background-color:lightgreen;
    opacity:0;
}

#container:hover #content {
    -webkit-animation:animUp 1s ease;
    animation-fill-mode:forwards;
    -webkit-animation-fill-mode:forwards;
}

@-webkit-keyframes animUp {
    0% {
        -webkit-transform:translateY(0);
        opacity:0;
    }
    100% {
        -webkit-transform:translateY(-100%);
        opacity:1;
    }
}

@-webkit-keyframes animDown {
    0% {
        -webkit-transform:translateY(-100%);
        opacity:1;
    }
    100% {
        -webkit-transform:translateY(0);
        opacity:0;
    }
}

<div id="container">
    <div id="content"></div>
</div>

Solution 3 - Use transitions

In your scenario, you can make this CSS only by replacing the keyframes with a transition instead, so it starts with opacity:0 and just the hover has a change in opacity and the transform:

#container {
    position:relative;
    width:100px;
    height:100px;
    border-style:inset;
}

#content {
    position:absolute;
    top:100px;
    width:100%;
    height:100%;
    background-color:lightgreen;

    /* initial state - hidden */
    opacity:0;
    /* set properties to animate - applies to hover and revert */
    transition:opacity 1s, transform 1s;
}

#container:hover #content {
    /* Just set properties to change - no need to change visibility */
    opacity:1;
    -webkit-transform:translateY(-100%);
    transform:translateY(-100%);
}

<div id="container">
    <div id="content"></div>
</div>

回答2:

I always set preload class to body with animation time value 0 and its working pretty well. I have some back going transitions so I have to remove load animation to them too. I solved this by temporary setting animation time to 0. You can change transitions to match yours.

HTML

... <body class="preload">...

CSS is setting animation to 0s

body.preload *{
animation-duration: 0s !important;
-webkit-animation-duration: 0s !important;
transition:background-color 0s, opacity 0s, color 0s, width 0s, height 0s, padding 0s, margin 0s !important;}

JS will remove class after some delay so animations can happen in normal time :)

setTimeout(function(){
    document.body.className="";
},500);

回答3:

Is there a way to do this pure CSS ?

Yes, absolutely : See the fork http://jsfiddle.net/5r32Lsme/2/ There is really no need for JS.

and I'd prefer it to run only after a hover event.

So you need to tell CSS what happens when it is NOT a hover event as well - in your example :

#container:not(:hover) #content {
  visibility: hidden;
  transition: visibility 0.01s 1s;
}    

But there are two things to note:

1) The transition delay above should match your animation duration

2) You can't use the property which you use to hide the animation onLoad in the animation. If you do need visibility in the animation, hide the animation initially like e.g.

#container:not(:hover) #content {
  top: -8000px;
  transition: top 0.01s 1s;
}    

A sidenote:

It is recommended to put native CSS properties after prefixed ones, so it should be

-webkit-animation-fill-mode: forwards;
animation-fill-mode: forwards;

and now there is a native transform

-webkit-transform: translateY(0);
transform: translateY(0);

回答4:

Rotation animation that (appears) not to run until needed.
The CSS below allows for up and down arrows for showing menu items. The animation does not appear to run on page load, but it really does.

@keyframes rotateDown {
   from { transform: rotate(180deg); }
   to   { transform: rotate(0deg); }
}

@keyframes rotateUp {
   from { transform: rotate(180deg); }
   to   { transform: rotate(0deg); }
}

div.menu input[type='checkbox'] + label.menu::before {
   display            :inline-block;
   content            : "▼";
   color              : #b78369;
   opacity            : 0.5;
   font-size          : 1.2em;
}

div.menu input[type='checkbox']:checked + label.menu::before {
   display            : inline-block;
   content            : "▲";
   color              : #b78369;
   opacity            : 0.5;
   font-size          : 1.2em;
}

div.menu input[type='checkbox'] + label.menu {
   display            : inline-block;
   animation-name     : rotateDown;
   animation-duration : 1ms;
}

div.menu input[type='checkbox']:checked + label.menu {
   display            : inline-block;
   animation-name     : rotateUp;
   animation-duration : 1ms;
}

div.menu input[type='checkbox'] + label.menu:hover {
   animation-duration : 500ms;
}

div.menu input[type='checkbox']:checked + label.menu:hover {
   animation-duration : 500ms;
}

From top to bottom:

1. Create the rotations. For this there are two... one for the down arrow and one for the up arrow. Two arrows are needed, because, after the rotation, they return to their natural state. So, the down arrow starts up and rotates down, while the up arrow starts down and rotates up.
2. Create the little arrows. This is a straight forward implementation of ::before
3. We put the animation on the label. There is nothing special, there, except that the animation duration is 1ms.
4. The mouse drives the animation speed. When the mouse hovers over the element, the animation-duration is set to enough time to seem smooth.

Working on my site