网格是使用 CSS flexbox 实现的。 Example:



此示例中的行数为 4，因为我出于演示目的固定了容器宽度。但是，实际上，它可以根据容器的宽度而改变(例如，如果用户调整窗口大小)。尝试在 this example 中调整输出窗口的大小去感受一下。

总是有一个事件元素，用黑色边框标记。

使用 JavaScript，我允许用户使用左/右箭头导航到上一个/下一个元素。在我的实现中，我只是将事件项的索引减少/增加 1。

现在，我还想允许用户向上/向下导航。为此，我只需要通过 <amount of items in a row> 减少/增加事件元素的索引。 .但是，鉴于它取决于容器的宽度，我该如何计算这个数字？有没有更好的方法来实现向上/向下功能？

.grid {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
  width: 250px;
  height: 200px;
  background-color: #ddd;
  padding: 10px 0 0 10px;
}

.item {
  width: 50px;
  height: 50px;
  background-color: red;
  margin: 0 10px 10px 0;
}

.active.item {
  outline: 5px solid black;
}

<div id="grid" class="grid">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item active"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

最佳答案

这个问题比查找一行中有多少元素稍微复杂一些。

最终，我们想知道事件元素的上方、下方、左侧和右侧是否有元素。这需要考虑底行不完整的情况。例如，在下面的情况下，事件元素没有上方、下方或右侧的元素:



但是，为了确定事件元素的上方/下方/左侧/右侧是否有元素，我们需要知道一行中有多少元素。

查找每行的元素数

要获得每行的元素数，我们需要:

const itemStyle = singleItem.currentStyle || window.getComputedStyle(active);
const itemWidth = singleItem.offsetWidth + parseFloat(itemStyle.marginLeft) + parseFloat(itemStyle.marginRight);

const gridStyle = grid.currentStyle || window.getComputedStyle(grid);
const gridWidth = grid.clientWidth - (parseFloat(gridStyle.paddingLeft) + parseFloat(gridStyle.paddingRight));

const numPerRow = Math.floor(gridWidth / itemWidth)

const grid = Array.from(document.querySelector("#grid").children);
const baseOffset = grid[0].offsetTop;
const breakIndex = grid.findIndex(item => item.offsetTop > baseOffset);
const numPerRow = (breakIndex === -1 ? grid.length : breakIndex);

const getNumPerRow = (selector) => {
  const grid = Array.from(document.querySelector(selector).children);
  const baseOffset = grid[0].offsetTop;
  const breakIndex = grid.findIndex(item => item.offsetTop > baseOffset);
  return (breakIndex === -1 ? grid.length : breakIndex);
}

.grid {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
  width: 400px;
  background-color: #ddd;
  padding: 10px 0 0 10px;
  margin-top: 5px;
  resize: horizontal;
  overflow: auto;
}

.item {
  width: 50px;
  height: 50px;
  background-color: red;
  margin: 0 10px 10px 0;
}

.active.item {
  outline: 5px solid black;
}

<button onclick="alert(getNumPerRow('#grid'))">Get Num Per Row</button>

<div id="grid" class="grid">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item active"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

<div id="grid" class="grid">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item active"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

const navigateGrid = (gridSelector, activeClass, direction) => {
  const grid = document.querySelector(gridSelector);
  const active = grid.querySelector(`.${activeClass}`);
  const activeIndex = Array.from(grid.children).indexOf(active);

  const gridChildren = Array.from(grid.children);
  const gridNum = gridChildren.length;
  const baseOffset = gridChildren[0].offsetTop;
  const breakIndex = gridChildren.findIndex(item => item.offsetTop > baseOffset);
  const numPerRow = (breakIndex === -1 ? gridNum : breakIndex);

  const updateActiveItem = (active, next, activeClass) => {
    active.classList.remove(activeClass);
    next.classList.add(activeClass); 
  }
  
  const isTopRow = activeIndex <= numPerRow - 1;
  const isBottomRow = activeIndex >= gridNum - numPerRow;
  const isLeftColumn = activeIndex % numPerRow === 0;
  const isRightColumn = activeIndex % numPerRow === numPerRow - 1 || activeIndex === gridNum - 1;
  
  switch (direction) {
    case "up":
      if (!isTopRow)
        updateActiveItem(active, gridChildren[activeIndex - numPerRow], activeClass);
      break;
    case "down":
      if (!isBottomRow)
        updateActiveItem(active, gridChildren[activeIndex + numPerRow], activeClass);
      break;  
    case "left":
      if (!isLeftColumn)
        updateActiveItem(active, gridChildren[activeIndex - 1], activeClass);
      break;   
    case "right":
      if (!isRightColumn)
        updateActiveItem(active, gridChildren[activeIndex + 1], activeClass);    
      break;
  }
}

.grid {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
  width: 400px;
  background-color: #ddd;
  padding: 10px 0 0 10px;
  margin-top: 5px;
  resize: horizontal;
  overflow: auto;
}

.item {
  width: 50px;
  height: 50px;
  background-color: red;
  margin: 0 10px 10px 0;
}

.active.item {
  outline: 5px solid black;
}

<button onClick='navigateGrid("#grid", "active", "up")'>Up</button>
<button onClick='navigateGrid("#grid", "active", "down")'>Down</button>
<button onClick='navigateGrid("#grid", "active", "left")'>Left</button>
<button onClick='navigateGrid("#grid", "active", "right")'>Right</button>

<div id="grid" class="grid">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item active"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

关于javascript - 如何计算连续 flexbox 元素的数量？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49043684/