Jquery carousel effect implementation process analysis_jquery

Carousel is the second animation implemented when learning jquery, and it is also the one that takes the longest to learn. In the process of implementing the carousel, we always encounter various problems. I have consulted many people and asked Guan Niang many times. Today, I dare not boldly say that I can write a carousel right away. I hope to record some of my thinking processes through essays.

The first is the html structure, a simple carousel, a seamless carousel of a single picture, mainly divided into three layers: div>ul>li, and the img picture inside the li.

Secondly, css style: div fixed width and height, overflow: hidden; the width of ul is recommended to be obtained dynamically (the next step will be about how to obtain it); regarding li, I am used to using floats, so that they can be arranged in order, on the ul Remember to clear float (clear: both).

The important thing is the jquery method, the main ones used are animate(), setInterval(), hover(). Before writing the method, let’s clarify the logic of the dynamic effect: the pictures slide from right to left in a loop. When the last picture is slid, the first picture is displayed, and so on.

1. Get the number of li length and width

var len=$('li').length,
  liWidth=$('li').width,

Because it is a seamless carousel, we have to do something to achieve a natural transition. When the picture slides to the last picture, how can we make a natural transition to the first picture? At this time, if the third picture Just one piece after the last one is fine. Therefore, we need to clone the first piece and append it to the end of li

$('li:first').clone().appendTo('ul')
2. Get the width of ul: the width of ul is equal to the width of all li plus the width of the cloned li

ulWidth=liWidth*(len+1)
It seems that the preparations are done, so next we try to make him move. The first thing that comes to mind is the animate() method:

animate( properties [, duration ] [, easing ] [, complete ] ),

The first parameter properties: css attributes and value objects, which determine the effect of the animation, whether it is up and down or left and right;

The second parameter duration: the time to complete an animation, the default is 400, the unit is milliseconds;

The third parameter easing: the easing function used for animation transition, the default is swing (linear, swing), this parameter is generally not used;

The fourth parameter complete: refers to the operation performed after completing the animation.

Our animation is from right to left, so we can achieve it by changing the margin-left value of ul

$('ul').animate({
  'marign-left': -liWidth*index
},3000,function(){
  if(index==len){
   index=0;
   $('ul').css({'margin-left':'0px'})
  } 
})  

The index refers to the index value of li. When the index value of li is equal to the length value of li, that is, the animation has been executed to the last picture, then directly set the margin-left of ul to 0 and the index value of li Also 0.

There is another hidden danger in this, which I won’t mention for now.

Next step, when the mouse leaves the div, the picture will automatically play. This is to use hover() and setInterval()

setInterval() is explained by W3C as follows: call a function or calculate an expression according to the specified period (in milliseconds). The function is called continuously until clearInterval() is called or the window is closed.

var autoPlay;
$('div').hover(function(){
  clearInterval(autoPlay); 
},function(){
  autoPlay=setInterval(function(){

$('ul').animate({

'marign-left': -liWidth*index
},3000,function(){
  if(index==len){
   index=0;
   $('ul').css({'margin-left':'0px'})；
　　　　index++;
  } 
});
}，3000) 
}).trigger('mouseleave');

In this way, an automatic playback function seems to be implemented, but we can also find a bug. The first frame seems to stay a bit long. Why?

This problem was solved yesterday. When the last picture is executed, its index immediately changes to 0, and then it will be executed twice. Therefore, in this judgment, we need to let it when the index is 0. Add 1, index++, and put it under the judgment condition.

There is another problem, which I discovered yesterday. There are two times in this carousel, one is the animation execution time, and the other is the playback time. The former time must be smaller than the latter time. The reason is that js The execution order is top-down. If the times are consistent or the latter time is smaller than the former, then within this time difference, the animation will not be able to enter the judgment conditions and will continue to play, so the carousel will fail. That’s it for today. Next time I share it, I’ll add a carousel effect of left and right arrows and hover dots.

Attached is the complete code:

<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>轮播</title>
  <style>
    body,p,form,input,button,dl,dt,dd,ul,ol,li,h1,h2,h3,h4{margin:0;padding:0;list-style:none;}
    body,button,input,select,textarea{font:12px Arial, Helvetica, sans-serif;color:#333;}
    input,select,textarea{font-size:100%;}
    .clearfix:after{display:block;content:".";height:0;visibility:hidden;clear:both;font-size:0;line-height:0;}
    .clearfix{*zoom:1;}
    .big-screen{width: 100%; height: 400px; overflow: hidden; margin: 40px 0;}
    .pic-list{height: 400px;}
    .pic-list li{float: left; width: 1920px; height: 400px;}
   </style>
</head>
<body>
  <div class="big-screen">
    <ul class="pic-list clearfix">
      <li>
        <a href="javascript:;">
          <img src="http://fed.yhd.cn:9000/1920x400/27ae60xfff" alt="picture" width="1920" height="400"/>
        </a>
      </li>
      <li>
        <a href="javascript:;">
          <img src="http://fed.yhd.cn:9000/1920x400/ae273axfff" alt="picture" width="1920" height="400"/>
        </a>
      </li>
      <li>
        <a href="javascript:;">
          <img src="http://fed.yhd.cn:9000/1920x400/2757aexfff" alt="picture" width="1920" height="400"/>
        </a>
      </li>
      <li>
        <a href="javascript:;">
          <img src="http://fed.yhd.cn:9000/1920x400/ae7d27xfff" alt="picture" width="1920" height="400"/>
        </a>
      </li>
    </ul>
  </div>
</body>
<script type="text/javascript" src="http://libs.baidu.com/jquery/1.11.3/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var ul=$('.pic-list'),
      li=ul.find('li'),
      liW=li.outerWidth(true),
      liLen=li.length,
      index=0,
      autoPlay;
    li.first().clone().appendTo(ul);
    ul.css({'width':liW*(liLen+1),'margin-left':-liW*index});
    function play(){
      if(!ul.is('animated')){
        ul.stop().animate({
          'margin-left':-liW*index
        },480,function(){
          if(index>liLen){
            index=0;
            ul.css({'margin-left':-liW*index});
            index++;
          }
        });
      }
    }
    $('.big-screen').hover(function(){
      clearInterval(autoPlay);
    },function(){
      autoPlay=setInterval(function(){
        play();
        index++;
      },500)
    }).trigger('mouseleave');

})
</script>
</html>  

The above is the complete code of the jquery carousel effect shared with you. I hope it will be helpful to your learning.