网格布局的基本概念

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CSS网格布局引入了二维网格布局系统,可用于页面主要区域布局或小型用户界面。本文介绍了CSS网格布局与CSS水平布局。随后,将在本指南规范1中更详细地介绍概述中的功能新术语

什么是网格?

网格是一个水平线和垂直线相交组,一组定义列和其他行。在网格元素可以放置尊重这些列和行线.CSS网格布局具有以下特点:

固定轨道和灵活的尺寸

你可以根据需要添加额外行和列,如定义一个显式功能网格与网格布局,规范处理网格以外的内容,尽可能添加“一个融入多列的容器”。

Item配置

你可以使用行号,名称或定位网格的区域将项目放置在网格上的精确位置。网格还包含一种算法来控制未在网格上给出明确位置的项目的位置。

创建额外的轨道来保存内容

可以使用网格布局定义一个显式网格,但该规范还涉及在声明网格外添加的内容,如需要添加额外的行和列。包括添加“尽可能多的列,以适应容器”的功能。

对齐控制

网格包含对齐特征,以便我们可以控制一旦放置到网格区域中的物体对齐,以及整个网格如何对齐。

控制重叠内容

多个项目可以放置在网格单元格中,或者区域可以部分地彼此重叠。然后可以用这种分层进行控制("z-index")}}.

Grid是一个强大的规范,当与CSS的其他部分(如flexbox)结合使用时,可以帮助您创建以前不可能在CSS中构建的布局。这一切都是通过在网格容器上创建一个网格来开始的。

网格容器

我们通过在元素上声明display:grid或display:inline-grid来创建一个网格容器。一旦我们这样做,这个元素的所有直接的孩子将成为网格项。

在这个例子中,我有一个包含一个包装类的div,里面有五个子元素。

<div class="wrapper">
   <div>One</div>
   <div>Two</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>

我将wrapper作为一个网格容器。

.wrapper {
  display: grid;
}

在网络浏览器中,所有直接的孩子现在都是网格项目。当网格为项目创建单列列网格时,在将项目显示为网格之前,您将看不到任何差异。在这一点上,你可能会发现在Firefox Developer Edition中有用,该开发人员版具有Grid Inspector作为开发工具的一部分。如果你在Firefox中查看此示例并检查网格,则会在值网格旁边看到一个小图标。单击此处,此元素上的网格将覆盖在浏览器窗口中。

Using the Grid Highlighter in DevTools to view a grid

当你学习,然后工作与CSS网格布局这个工具会给你一个更好的想法是什么,你的网格可视化。

如果我们要开始使这样更多的网格,就像我们需要添加列轨。

网格轨道

We define rows and columns on our grid with the grid-template-columns and grid-template-rows properties. These define grid tracks. A grid track is the space between any two lines on the grid. In the below image you can see a track highlighter – the first row track in our grid.

我可以通过添加grid-template-columns属性添加到我们前面的例子,然后定义列轨迹的大小。

我现在创建了一个网格,三个200像素宽栏轨道。子项目将在每个网格单元中的网格上展开。

<div class="wrapper">
   <div>One</div>
   <div>Two</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>
.wrapper {
  display: grid;
  grid-template-columns: 200px 200px 200px;
}

fr单位

轨道可以使用任何长度单位进行定义。 Grid还引入了一个额外的长度单位来帮助我们创建灵活的网格轨道。新的fr单位代表网格容器中可用空间的一小部分。下一个网格定义将创建三个相等宽度的轨道,根据可用空间增长和收缩。

<div class="wrapper">
   <div>One</div>
   <div>Two</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>
.wrapper {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
}

在下面的这个例子中,我们创建一个定义一个2fr跟踪两1fr轨道。可用空间分割为四。两个部分给出了第一个轨道和一个部分到下两个。

.wrapper {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
}

在最终的例子中,我们将绝对尺寸的轨道与分数单位进行混合。第一个轨道是500像素,因此这个固定宽度被从可用空间中取走。剩下的空间被分为三个,并且与两个柔性轨道成比例地分配。

.wrapper {
  display: grid;
  grid-template-columns: 500px 1fr 2fr;
}

具有repeat()符号表示轨道列表

具有许多轨道的大网格可以使用repeat()符号重复轨道列表的所有或部分。例如网格定义:

.wrapper {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
}

也可以写成:

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
}

Repeat notation can be used for a part of the track listing. In this next example I have created a grid with an initial 20-pixel track, then a repeating section of 6 1fr tracks then a final 20-pixel track.

.wrapper {
  display: grid;
  grid-template-columns: 20px repeat(6, 1fr) 20px;
}

在下一个示例中我创建了一个网格,重复标记6 1 fr和20像素可用于轨道清单的一部分。

.wrapper {
  display: grid;
  grid-template-columns: repeat(5, 1fr 2fr);
}

隐式和显式网格

When creating our example grid we defined our column tracks with the grid-template-columns property, but let grid create rows as needed for the content. These rows are created in the implicit grid. The explicit grid consists of the rows and columns you define with grid-template-columns and grid-template-rows. If you place something outside of that defined grid, or due to the amount of content more grid tracks are needed, then grid creates rows and columns in the implicit grid. These tracks will be auto-sized by default, so will size based on the content inside them.

You can also define a set size for tracks created in the implicit grid with the grid-auto-rows and grid-auto-columns properties.

In the below example we use grid-auto-rows to ensure that tracks created in the implicit grid are 200 pixels tall.

<div class="wrapper">
   <div>One</div>
   <div>Two</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>
.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-auto-rows: 200px;
}

Track sizing and minmax()

When setting up an explicit grid or defining the sizing for automatically created rows or columns we may want to give tracks a minimum size, but ensure they expand to fit any content that is added. For example, I may want my rows to never collapse smaller than 100 pixels, but if my content stretches to 300 pixels in height I would like the row to stretch to that height.

Grid has a solution for this with the minmax() function. In this next example I am using minmax() in the value of grid-auto-rows. Automatically created rows will be a minimum of 100 pixels tall, and a maximum of auto. Using auto means that the size will look at the content size and so stretch to give space for the tallest thing in a cell in this row.

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-auto-rows: minmax(100px, auto);
}
<div class="wrapper">
   <div>One</div>
   <div>Two
   <p>I have some more content in.</p>

<p>This makes me taller than 100 pixels.</p>
</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>

Grid Lines

It should be noted that when we define a grid we define the grid tracks, not the lines. Grid then gives us numbered lines to use when positioning items. In our three column, two row grid we have four column lines.

Diagram showing numbered grid lines.

Lines are numbered according to the writing mode of the document. In a left-to-right language, line 1 is on the left-hand side of the grid. In a right-to-left language, it is on the right-hand side of the grid. Lines can also be named, and we will look at how to do this in a later guide in this series.

Positioning items against lines

We will be exploring line based placement in full detail in a later article, the following example demonstrates doing this in a simple way. When placing an item we target the line – rather than the track.

In the following example I am placing the first two items on our three column track grid, using the grid-column-start, grid-column-end, grid-row-start and grid-row-end properties. Working from left to right, the first item is placed against column line 1, and spans to column line 4, which in our case is the far right line on the grid. It begins at row line 1 and ends at row line 3, therefore spanning two row tracks.

The second item starts on grid column line 1, and spans one track. This is the default so I do not need to specify the end line. It also spans two row tracks from row line 3 to row line 5. The other items will place themselves into empty spaces on the grid.

<div class="wrapper">
   <div class="box1">One</div>
   <div class="box2">Two</div>
   <div class="box3">Three</div>
   <div class="box4">Four</div>
   <div class="box5">Five</div>
</div>
.wrapper { 
    display: grid; 
    grid-template-columns: repeat(3, 1fr); 
    grid-auto-rows: 100px; 
} 
.box1 { 
    grid-column-start: 1; 
    grid-column-end: 4; 
    grid-row-start: 1; 
    grid-row-end: 3; 
} 
.box2 { 
    grid-column-start: 1; 
    grid-row-start: 3; 
    grid-row-end: 5; 
}

Don't forget that you can use the Grid Inspector in Firefox Developer Tools to see how the items are positioned against the lines of the grid.

Grid Cells

A grid cell is the smallest unit on a grid, conceptually it is like a table cell. As we saw in our earlier examples, once a grid is defined on a parent the child items will lay themselves out once in each cell of the defined grid. In the below image I have highlighted the first cell of the grid.

The first cell of the grid highlighted

Grid areas

Items can span one or more cells both by row or by column, and this creates a grid area. Grid areas have to be rectangular – it isn’t possible to create an L-shaped area for example. The highlighted grid area spans two row and two column tracks.

A grid area

Gutters

Gutters or alleys between grid cells can be created using the grid-column-gap and grid-row-gap properties, or the shorthand grid-gap. In the below example I am creating a 10-pixel gap between columns and a 1em gap between rows.

.wrapper {
   display: grid;
   grid-template-columns: repeat(3, 1fr);
   grid-column-gap: 10px;
   grid-row-gap: 1em;
}
<div class="wrapper">
   <div>One</div>
   <div>Two</div>
   <div>Three</div>
   <div>Four</div>
   <div>Five</div>
</div>

Any space used by gaps will be accounted for before space is assigned to flexible length fr tracks, and gaps act for sizing purposes like a regular grid track, however you cannot place anything into a gap. In terms of line-based positioning, the gap acts like a fat line.

Nesting grids

A grid item can become a grid container. In the following example I have the three-column grid created earlier, with our two positioned items. In this case the first item has some sub-items. As these items are not direct children of the grid they do not participate in grid layout and so display in normal document flow.

<div class="wrapper">
   <div class="box box1">
       <div class="nested">a</div>
       <div class="nested">b</div>
        <div class="nested">c</div>
    </div>
    <div class="box box2">Two</div>
    <div class="box box3">Three</div>
    <div class="box box4">Four</div>
    <div class="box box5">Five</div>
</div>

Nested grid in flow

If I set box1 to display: grid I can give it a track definition and it too will become a grid, the items then lay out on this new grid.

.box1 {
   grid-column-start: 1;
   grid-column-end: 4;
   grid-row-start: 1;
   grid-row-end: 3;
   display: grid;
   grid-template-columns: repeat(3, 1fr);
}

In this case the nested grid has no relationship to the parent. As you can see in the example it has not inherited the grid-gap of the parent and the lines in the nested grid do not align to the lines in the parent grid.

Subgrid

In the level 1 grid specification there is a feature called subgrid which would let us create nested grids that use the track definition of the parent grid.

Subgrids are not yet implemented in any browsers, and the specification is subject to change.

In the current specification, we would edit the above nested grid example to use display: subgrid rather than display: grid, then remove the track definition. The nested grid will use the parent grid tracks to lay out items.

It should be noted that the nested grid is in both dimensions—rows and columns. There is no concept of the implicit grid working with subgrids. This means you need to ensure that the parent grid has enough row and column tracks for all the subitems.

.box1 {
   grid-column-start: 1;
   grid-column-end: 4;
   grid-row-start: 1;
   grid-row-end: 3;
   display: subgrid;
}

Layering items with z-index

Grid items can occupy the same cell. If we return to our example with items positioned by line number, we can change this to make two items overlap.

<div class="wrapper">
   <div class="box box1">One</div>
   <div class="box box2">Two</div>
   <div class="box box3">Three</div>
   <div class="box box4">Four</div>
   <div class="box box5">Five</div>
</div>
.wrapper {
   display: grid;
   grid-template-columns: repeat(3, 1fr);
   grid-auto-rows: 100px;
}
.box1 {
   grid-column-start: 1;
   grid-column-end: 4;
   grid-row-start: 1;
   grid-row-end: 3;
}
.box2 {
   grid-column-start: 1;
   grid-row-start: 2;
   grid-row-end: 4;
}

The item box2 is now overlapping box1, it displays on top as it comes later in the source order.

Controlling the order

We can control the order in which items stack up by using the z-index property - just as with positioned items. If we give box2 a lower z-index than box1 it will display below box1 in the stack.

.wrapper {
   display: grid;
   grid-template-columns: repeat(3, 1fr);
   grid-auto-rows: 100px;
}
.box1 {
   grid-column-start: 1;
   grid-column-end: 4;
   grid-row-start: 1;
   grid-row-end: 3;
   z-index: 2;
}
.box2 {
   grid-column-start: 1;
   grid-row-start: 2;
   grid-row-end: 4;
   z-index: 1;
}

下一个步骤

In this article we have had a very quick look through the Grid Layout Specification. Have a play with the code examples, and then move onto the next part of this guide where we will really start to dig into the detail of CSS Grid Layout.

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