使用javascript / jQuery添加类时，为什么css过渡不起作用？

Question

I have a message box which I want to slide down on click. I do this by adding a css class through Angular (and jQuery in my example). But my CSS transition does not take effect.

Is there any obvious mistake I'm doing?

Here's my fiddle: http://jsfiddle.net/mBKXn/

and my code:

// jQuery
$('.test').on('click',function(){
  $('#msgContainer').toggleClass('msgShow');
});

// HTML
<div class="container">
    <div id="msgContainer" class="msg">
        <p>Message here</p>
        <p>T2</p>
        <p>T4</p>
    </div>
    Test text
</div>

<button class="test">Click</button>

// CSS
.container{
    position: relative;
    height: 200px;
    width: 400px;
    border: solid 1px #222;
}

.msg{
    position: absolute;
    top: 0;
    background-color: #FEEFB3;
    height: 0;
    width: 100%;
    overflow: hidden;
    -webkit-transition: height 0.8s linear;
    -moz-transition: height 0.8s linear;
    -o-transition: height 0.8s linear;
    -ms-transition: height 0.8s linear;
    transition: height 0.8s linear;    
}

.msgShow{
    height: auto;
}

Answer 1

To animate height from 0 to auto you have to use max-height instead:

.msg{
    position: absolute;
    top: 0;
    background-color: #FEEFB3;
    max-height: 0;
    width: 100%;
    overflow: hidden;
    -webkit-transition: max-height 0.8s linear;
    -moz-transition: max-height 0.8s linear;
    -o-transition: max-height 0.8s linear;
    -ms-transition: max-height 0.8s linear;
    transition: max-height 0.8s linear;    
}

.msgShow{
    max-height: 1000px;
}

Seems to work: http://jsfiddle.net/mBKXn/3/

Also take a look at this question .

Answer 2

you need to set a defined height. Height:auto won't work as this is the default height value.

see the specs for the height property here: http://www.w3.org/TR/CSS2/visudet.html#the-height-property

http://jsfiddle.net/mBKXn/7/

.msgShow{
    height: 100%;
}

Answer 3

Another (older IE compliant) way to do this is through slideToggle.

Updated Fiddle that works and another Fiddle where I removed some of your transition css and it makes the animation smoother in my opinion.

your code needs a slight change:

$('.test').on('click',function(){
  $('#msgContainer').slideToggle('slow');
});

and your class needs a slight change:

.msg{
    display:none;
    position: absolute;
    top: 0;
    background-color: #FEEFB3;
    height: auto;
    width: 100%;
    overflow: hidden;
}