问题描述

我正在构建一个 carousel，非常简约，使用 CSS捕捉点.拥有 仅 CSS 选项 对我来说很重要，但我可以使用 javascript 进行一些改进(无框架).

I am building a carousel, very minimalist, using CSS snap points. It is important for me to have CSS only options, but I'm fine with enhancing a bit with javascript (no framework).

我正在尝试添加上一个和下一个按钮，以编程方式滚动到下一个或上一个元素.如果 javascript 被禁用，按钮将被隐藏并且轮播仍然有效.

I am trying to add previous and next buttons to scroll programmatically to the next or previous element. If javascript is disabled, buttons will be hidden and carousel still functionnal.

我的问题是关于如何触发滚动到下一个捕捉点?

所有项目都有不同的大小，我发现的大多数解决方案需要像素值(如示例中使用的scrollBy).scrollBy 40px 适用于第 2 页，但不适用于其他页面，因为它们太大(基于视口的大小).

All items have different size, and most solution I found require pixel value (like scrollBy used in the exemple). A scrollBy 40px works for page 2, but not for others since they are too big (size based on viewport).

function goPrecious() {
  document.getElementById('container').scrollBy({ 
    top: -40,
    behavior: 'smooth' 
  });
}

function goNext() {
  document.getElementById('container').scrollBy({ 
    top: 40,
    behavior: 'smooth' 
  });
}

#container {
  scroll-snap-type: y mandatory;
  overflow-y: scroll;

  border: 2px solid var(--gs0);
  border-radius: 8px;
  height: 60vh;
}

#container div {
  scroll-snap-align: start;

  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 4rem;
}
#container div:nth-child(1) {
  background: hotpink;
  color: white;
  height: 50vh;
}
#container div:nth-child(2) {
  background: azure;
  height: 40vh;
}
#container div:nth-child(3) {
  background: blanchedalmond;
  height: 60vh;
}
#container div:nth-child(4) {
  background: lightcoral;
  color: white;
  height: 40vh;
}

<div id="container">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
</div>

<button onClick="goPrecious()">previous</button>
<button onClick="goNext()">next</button>

推荐答案

好问题！我将此视为挑战.
所以，我增加了 JavaScript 让它动态工作.按照我的详细解决方案(最后是完整代码):

Nice question! I took this as a challenge.
So, I increased JavaScript for it to work dynamically. Follow my detailed solution (in the end the complete code):

首先在.container中添加position: relative，因为scroll和height需要参考code> 检查 .container.

First, add position: relative to the .container, because it need to be reference for scroll and height checkings inside .container.

然后，我们创建3个全局辅助变量:

Then, let's create 3 global auxiliary variables:

1) 将项目滚动位置(顶部和底部)作为arrays 放入array.示例:[[0, 125], [125, 280], [280, 360]](本例中为 3 项).
3) 一个存储一半 .container height (以后会有用).
2)另一个存储item index的scroll位置

1) One to get items scroll positions (top and bottom) as arrays into an array. Example: [[0, 125], [125, 280], [280, 360]] (3 items in this case).
3) One that stores half of .container height (it will be useful later).
2) Another one to store the item index for scroll position

var carouselPositions;
var halfContainer;
var currentItem;

现在，一个名为 getCarouselPositions 的 函数 创建了带有项目位置的 array(存储在 carouselPositions 中)和计算 .container 的一半(存储在 halfContainer 中):

Now, a function called getCarouselPositions that creates the array with items positions (stored in carouselPositions) and calculates the half of .container (stored in halfContainer):

function getCarouselPositions() {
  carouselPositions = [];
  document.querySelectorAll('#container div').forEach(function(div) {
    carouselPositions.push([div.offsetTop, div.offsetTop + div.offsetHeight]); // add to array the positions information
  })
  halfContainer = document.querySelector('#container').offsetHeight/2;
}

getCarouselPositions(); // call it once

让我们替换 buttons 上的 functions.现在，当您单击它们时，将调用相同的 function，但带有 "next" 或 "previous" 参数:

Let's replace the functions on buttons. Now, when you click on them, the same function will be called, but with "next" or "previous" argument:

<button onClick="goCarousel('previous')">previous</button>
<button onClick="goCarousel('next')">next</button>

这里是关于 goCarousel function 本身的:

Here is about the goCarousel function itself:

首先，它创建2个变量，分别存储top scroll位置和bottom scroll位置.

First, it creates 2 variables that store top scroll position and bottom scroll position of carousel.

然后，有 2 个条件来查看当前轮播位置是在大多数 top 还是大多数 bottom.
如果它在top 并点击"next" 按钮，它将转到第二个项目的位置.如果它在bottom并点击"previous"按钮，它将转到最后一项之前的上一个.

Then, there are 2 conditionals to see if the current carousel position is on most top or most bottom.
If it's on top and clicked "next" button, it will go to the second item position. If it's on bottom and clicked "previous" button, it will go the previous one before the last item.

如果两个条件都失败，则表示当前项目不是第一个或最后一个.因此，它会检查当前位置是什么，在循环中使用容器的一半与位置数组进行计算以查看item 正在显示.然后，它结合 "previous" 或 "next" 检查为 currentItem 变量设置正确的下一个位置.

var carouselPositions;
var halfContainer;
var currentItem;

function getCarouselPositions() {
  carouselPositions = [];
  document.querySelectorAll('#container div').forEach(function(div) {
    carouselPositions.push([div.offsetTop, div.offsetTop + div.offsetHeight]); // add to array the positions information
  })
  halfContainer = document.querySelector('#container').offsetHeight/2;
}

getCarouselPositions(); // call it once

function goCarousel(direction) {
  
  var currentScrollTop = document.querySelector('#container').scrollTop;
  var currentScrollBottom = currentScrollTop + document.querySelector('#container').offsetHeight;
  
  if (currentScrollTop === 0 && direction === 'next') {
      currentItem = 1;
  } else if (currentScrollBottom === document.querySelector('#container').scrollHeight && direction === 'previous') {
      console.log('here')
      currentItem = carouselPositions.length - 2;
  } else {
      var currentMiddlePosition = currentScrollTop + halfContainer;
      for (var i = 0; i < carouselPositions.length; i++) {
        if (currentMiddlePosition > carouselPositions[i][0] && currentMiddlePosition < carouselPositions[i][1]) {
          currentItem = i;
          if (direction === 'next') {
              currentItem++;
          } else if (direction === 'previous') {
              currentItem--    
          }
        }
      }
  } 
  
  document.getElementById('container').scrollTo({
    top: carouselPositions[currentItem][0],
    behavior: 'smooth' 
  });
  
}
window.addEventListener('resize', getCarouselPositions);

#container {
  scroll-snap-type: y mandatory;
  overflow-y: scroll;
  border: 2px solid var(--gs0);
  border-radius: 8px;
  height: 60vh;
  position: relative;
}

#container div {
  scroll-snap-align: start;

  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 4rem;
}
#container div:nth-child(1) {
  background: hotpink;
  color: white;
  height: 50vh;
}
#container div:nth-child(2) {
  background: azure;
  height: 40vh;
}
#container div:nth-child(3) {
  background: blanchedalmond;
  height: 60vh;
}
#container div:nth-child(4) {
  background: lightcoral;
  color: white;
  height: 40vh;
}

<div id="container">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
</div>

<button onClick="goCarousel('previous')">previous</button>
<button onClick="goCarousel('next')">next</button>

window.addEventListener('resize', getCarouselPositions);