传统的布局方法

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在CSS布局中,网格系统是一种非常常见的布局方式, 并且在CSS 网格布局之前,他们倾向于用浮动和其他的布局功能。你可以想象你的布局采用不同的列(e.g. 4, 6, or 12), 然后把你的内容填充到这些想象的列中. 这篇文章将要探讨这种古老的方法是怎么实现的,来帮助你在旧项目工作时更好的理解他们。

Prerequisites: HTML 基础(学习 Introduction to HTML),并且了解CSS是怎么工作的(学习 Introduction to CSS and Styling boxes.)
Objective: 了解浏览器CSS网格布局系统的基本概念。

在CSS网格布局之前的布局与网格系统

对于一个有设计经验的人来说他们也许会非常惊讶CSS直到最近才有网格系统,取而代之,我们用了许多次优方法来完成网格设计。我们现在把这些称为“古老”的方法。

对于许多新项目,大多数情况下CSS网格布局(CSS Grid Layout)被用来和其他一个或多个现代的布局方法结合形成布局的基础。但是你会时不时的遇到采用这种古老方法的“网格系统”。这很值得了解他们是如何工作的,以及为什么他们和CSS网格布局不同。

这个课程将会解释网格系统和网格框架是如何基于float和flexbox的。学习过网格布局之后你可能会惊讶这些看起来有多复杂!这些知识将会变的十分有用如果你需要在创建不支持新技术的老浏览器上创建后备代码,并且你也可以在用这些类别的项目中工作。

值得随时注意的是,在我们探索这些系统时,没有一个网格建立的方式是通过CSS网格布局创建网格的。他们通过给目标一个大小, 然后推动他们让他们像网格一样排列起来。

两列布局

让我们从最简单的实例开始——两列布局。你可以根据步骤创建一个新的 index.html 在你的电脑上,先拷贝这个框架 simple HTML template,然后在适当的位置填充下面的代码。在底部的区域你可以看到一个最终代码是什么样的实时实例。

首先,我们需要在我们的栏中放入一些内容。把现在在body中的内容替换成下面的部分:

<h1>2 column layout example</h1>
<div>
  <h2>First column</h2>
  <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla luctus aliquam dolor, eu lacinia lorem placerat vulputate. Duis felis orci, pulvinar id metus ut, rutrum luctus orci. Cras porttitor imperdiet nunc, at ultricies tellus laoreet sit amet. Sed auctor cursus massa at porta. Integer ligula ipsum, tristique sit amet orci vel, viverra egestas ligula. Curabitur vehicula tellus neque, ac ornare ex malesuada et. In vitae convallis lacus. Aliquam erat volutpat. Suspendisse ac imperdiet turpis. Aenean finibus sollicitudin eros pharetra congue. Duis ornare egestas augue ut luctus. Proin blandit quam nec lacus varius commodo et a urna. Ut id ornare felis, eget fermentum sapien.</p>
</div>

<div>
  <h2>Second column</h2>
  <p>Nam vulputate diam nec tempor bibendum. Donec luctus augue eget malesuada ultrices. Phasellus turpis est, posuere sit amet dapibus ut, facilisis sed est. Nam id risus quis ante semper consectetur eget aliquam lorem. Vivamus tristique elit dolor, sed pretium metus suscipit vel. Mauris ultricies lectus sed lobortis finibus. Vivamus eu urna eget velit cursus viverra quis vestibulum sem. Aliquam tincidunt eget purus in interdum. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus.</p>
</div>

每一列都需要一个外部元素来包含内容,让我们一次操作所有内容。在这个例子中我们选择了<div>, 但是你可以选择其他更合适的语句,例如<article><section>, 和 <aside>,或者是其他别的。

现在我们来看css。首先,应用以下的代码来对HTML进行基本设置:

body {
  width: 90%;
  max-width: 900px;
  margin: 0 auto;
}

body将会占90%的视野宽度直到达到900px,在这种情况下,它将固定并保持在窗口正中。 默认情况下,他的子项 (the <h1> 和两个 <div>) 将会达到正文宽度的100%。如果我们希望两个<div>一个浮在窗口的一边另一个浮动在另一边的话, 我们需要将他们的宽度设置为其父元素的100%或则更小,以便他们可以并排放置。将下面的代码加在CSS的底部:

div:nth-of-type(1) {
  width: 48%;
}

div:nth-of-type(2) {
  width: 48%;
}

这里我们将他们都设置为父元素宽度的48%——总共是96%,在两栏之间留4% 的空隙,为他们提供一些宽松的空间。现在我们只需要将他们float,像这样:

div:nth-of-type(1) {
  width: 48%;
  float: left;
}

div:nth-of-type(2) {
  width: 48%;
  float: right;
}

将这些都组合起来会得到这样的结果:

你有没有注意到我们在宽度的表示上都用的是百分比——这是一个很好的策略,因为他创建了一个流动布局(liquid layout),他能够适应不同的屏幕大小,并且在小一些的屏幕上也能使列保持一样的比例。试一试自己来调整浏览器窗口的宽度吧~ 这是响应式网页非常有价值的一个工具哦~

Note:你可以通过点击  0_two-column-layout.html 看到这个实例(或者 the source code)。

创建简单的原始网格框架

大多数古老的框架使用float属性来使列相邻排列,让他们看起来像使一个网格。学习用float创建网格可以展示他们工作的的原理,并且介绍了一些更高级的概念来搭建你在课程floats and clearing中学到的内容。

最简单的网格创建是固定宽度——我们通常只需要计算设计中总的宽度,列的数目,每一列和间隔的宽度。但是,如果我们决定设计的网格是可以根据浏览器宽度缩放的,我们则需要计算每一列和间距的所占的宽度的百分比。

下一部分我们将学习如何创建这两种方式的网格。我们会构建一个有12列的表格——我们选择了12这个常见的数字,来看他对不同情景的适应情况,因为12可以被6,4,3,和2完全整除。

一个简单的固定宽度网格

让我们先来创建一个固定列宽度的网格系统吧~

首先,把 simple-grid.html 下载储存下来,他的body中包含以下的标记:

<div class="wrapper">
  <div class="row">
    <div class="col">1</div>
    <div class="col">2</div>
    <div class="col">3</div>
    <div class="col">4</div>
    <div class="col">5</div>
    <div class="col">6</div>
    <div class="col">7</div>
    <div class="col">8</div>
    <div class="col">9</div>
    <div class="col">10</div>
    <div class="col">11</div>
    <div class="col">12</div>
  </div>
  <div class="row">
    <div class="col span1">13</div>
    <div class="col span6">14</div>
    <div class="col span3">15</div>
    <div class="col span2">16</div>    
  </div>
</div>

我们的目标是把它变成一个有两行十二列的演示网格——第一行显示各列的大小,第二行显示网格上不同大小的区域。

在 <style>中,加入下面的代码,使容器的右侧的padding宽度为20像素,总的宽度变为980像素。这样给我们留出960像素可以放置列和他们的间隔——这种情况下,padding会被从总的内容宽度中减去,因为我们在box-sizing中讲所有的元素设置成了border-box (可以查看Changing the box model completely获得更多信息和解释)。

* {
  box-sizing: border-box;
}
    
body {
  width: 980px;
  margin: 0 auto;
}

.wrapper {
  padding-right: 20px;
}

Now use the row container that is wrapped around each row of the grid to clear one row from another. Add the following rule below your previous one:

.row {
  clear: both;
}

Applying this clearing means that we don’t need to completely fill each row with elements making the full twelve columns. The rows will remain separated, and not interfere with each other.

The gutters between the columns are 20 pixels wide. We create these gutters as a margin on the left side of each column — including the first column, to balance out the 20 pixels of padding on the right hand side of the container. So we have 12 gutters in total — 12 x 20 = 240.

We need to subtract that from our total width of 960 pixels, giving us 720 pixels for our columns. If we now divide that by 12, we know that each column should be 60 pixels wide.

Our next step is to create a rule for the class .col,  floating it left, giving it a margin-left of 20 pixels to form the gutter, and a width of 60 pixels. Add the following rule to the bottom of your CSS:

.col {
  float: left;
  margin-left: 20px;
  width: 60px;
  background: rgb(255, 150, 150);
}

The top row of single columns will now lay out neatly as a grid.

Note: We've also given each column a light red color so you can see exactly how much space each one takes up.

Layout containers that we want to span more than one column need to be given special classes to adjust their width values to the required number of columns (plus gutters in between). We need to create an additional class to allow containers to span 2 to 12 columns. Each width is the result of adding up the column width of that number of columns plus the gutter widths, which will always number one less than the number of columns.

Add the following at the bottom of your CSS:

/* Two column widths (120px) plus one gutter width (20px) */
.col.span2 { width: 140px; }
/* Three column widths (180px) plus two gutter widths (40px) */
.col.span3 { width: 220px; }
/* And so on... */
.col.span4 { width: 300px; }
.col.span5 { width: 380px; }
.col.span6 { width: 460px; }
.col.span7 { width: 540px; }
.col.span8 { width: 620px; }
.col.span9 { width: 700px; }
.col.span10 { width: 780px; }
.col.span11 { width: 860px; }
.col.span12 { width: 940px; }

With these classes created we can now lay out different width columns on the grid. Try saving and loading the page in your browser to see the effects.

Note: If you are having trouble getting the above example to work, try comparing it against our finished version on GitHub (see it running live also).

Try modifying the classes on your elements or even adding and removing some containers, to see how you can vary the layout. For example, you could make the second row look like this:

<div class="row">
  <div class="col span8">13</div>
  <div class="col span4">14</div>
</div>

Now you've got a grid system working, you can simply define the rows and the number of columns in each row, then fill each container with your required content. Great!

Creating a fluid grid

Our grid works nicely, but it has a fixed width. We really want a flexible (fluid) grid that will grow and shrink with the available space in the browser viewport. To achieve this we can turn the reference pixel widths into percentages.

The equation that turns a fixed width into a flexible percentage-based one is as follows.

target / context = result

For our column width, our target width is 60 pixels and our context is the 960 pixel wrapper. We can use the following to calculate a percentage.

60 / 960 = 0.0625

We then move the decimal point 2 places giving us a percentage of 6.25%. So, in our CSS we can replace the 60 pixel column width with 6.25%.

We need to do the same with our gutter width:

20 / 960 = 0.02083333333

So we need to replace the 20 pixel margin-left on our .col rule and the 20 pixel padding-right on .wrapper with 2.08333333%.

Updating our grid

To get started in this section, make a new copy of your previous example page, or make a local copy of our simple-grid-finished.html code to use as a starting point.

Update the second CSS rule (with the .wrapper selector) as follows:

body {
  width: 90%;
  max-width: 980px;
  margin: 0 auto;
}

.wrapper {
  padding-right: 2.08333333%;
}

Not only have we given it a percentage width, we have also added a max-width property in order to stop the layout becoming too wide.

Next, update the fourth CSS rule (with the .col selector) like so:

.col {
  float: left;
  margin-left: 2.08333333%;
  width: 6.25%;
  background: rgb(255, 150, 150);
}

Now comes the slightly more laborious part — we need to update all our .col.span rules to use percentages rather than pixel widths. This takes a bit of time with a calculator; to save you some effort, we've done it for you below.

Update the bottom block of CSS rules with the following:

/* Two column widths (12.5%) plus one gutter width (2.08333333%) */
.col.span2 { width: 14.58333333%; }
/* Three column widths (18.75%) plus two gutter widths (4.1666666) */
.col.span3 { width: 22.91666666%; }
/* And so on... */
.col.span4 { width: 31.24999999%; }
.col.span5 { width: 39.58333332%; }
.col.span6 { width: 47.91666665%; }
.col.span7 { width: 56.24999998%; }
.col.span8 { width: 64.58333331%; }
.col.span9 { width: 72.91666664%; }
.col.span10 { width: 81.24999997%; }
.col.span11 { width: 89.5833333%; }
.col.span12 { width: 97.91666663%; }

Now save your code, load it in a browser, and try changing the viewport width — you should see the column widths adjust nicely to suit.

Note: If you are having trouble getting the above example to work, try comparing it against our finished version on GitHub (see it running live also).

Easier calculations using the calc() function

You could use the calc() function to do the math right inside your CSS — this allows you to insert simple mathematical equations into your CSS values, to calculate what a value should be. It is especially useful when there is complex math to be done, and you can even compute a calculation that uses different units, for example "I want this element's height to always be 100% of its parent's height, minus 50px". See this example from a MediaRecorder API tutorial.

Anyway, back to our grids! Any column that spans more than one column of our grid has a total width of 6.25% multiplied by the number of columns spanned plus 2.08333333% multiplied by the number of gutters (which will always be the number of columns minus 1). The calc() function allows us to do this calculation right inside the width value, so for any item spanning 4 columns we can do this, for example:

.col.span4 {
  width: calc((6.25%*4) + (2.08333333%*3));
}

Try replacing your bottom block of rules with the following, then reload it in the browser to see if you get the same result:

.col.span2 { width: calc((6.25%*2) + 2.08333333%); }
.col.span3 { width: calc((6.25%*3) + (2.08333333%*2)); }
.col.span4 { width: calc((6.25%*4) + (2.08333333%*3)); }
.col.span5 { width: calc((6.25%*5) + (2.08333333%*4)); }
.col.span6 { width: calc((6.25%*6) + (2.08333333%*5)); }
.col.span7 { width: calc((6.25%*7) + (2.08333333%*6)); }
.col.span8 { width: calc((6.25%*8) + (2.08333333%*7)); }
.col.span9 { width: calc((6.25%*9) + (2.08333333%*8)); }
.col.span10 { width: calc((6.25%*10) + (2.08333333%*9)); }
.col.span11 { width: calc((6.25%*11) + (2.08333333%*10)); }
.col.span12 { width: calc((6.25%*12) + (2.08333333%*11)); }

Note: You can see our finished version in fluid-grid-calc.html (also see it live).

Note: If you can't get this to work, it might be because your browser does not support the calc() function, although it is fairly well supported across browsers — as far back as IE9.

Semantic versus “unsemantic” grid systems

Adding classes to your markup to define layout means that your content and markup becomes tied to your visual presentation. You will sometimes hear this use of CSS classes described as being “unsemantic” — describing how the content looks — rather than a semantic use of classes that describes the content. This is the case with our span2, span3, etc., classes.

These are not the only approach. You could instead decide on your grid and then add the sizing information to the rules for existing semantic classes. For example, if you had a <div> with a class of content on it that you wanted to span 8 columns, you could copy across the width from the span8 class, giving you a rule like so:

.content {
  width: calc((6.25%*8) + (2.08333333%*7));
}

Note: If you were to use a preprocessor such as Sass, you could create a simple mixin to insert that value for you.

Enabling offset containers in our grid

The grid we have created works well as long as we want to start all of the containers flush with the left hand side of the grid. If we wanted to leave an empty column space  before the first container — or between containers — we would need to create an offset class to add a left margin to our site to push it across the grid visually. More math!

Let's try this out.

Start with your previous code, or use our fluid-grid.html file as a starting point.

Let's create a class in our CSS that will offset a container element by one column width. Add the following to the bottom of your CSS:

.offset-by-one {
  margin-left: calc(6.25% + (2.08333333%*2));
}

Or if you prefer to calculate the percentages yourself, use this one:

.offset-by-one {
  margin-left: 10.41666666%;
}

You can now add this class to any container you want to leave a one column wide empty space on the left hand side of it. For example, if you have this in your HTML:

<div class="col span6">14</div>

Try replacing it with

<div class="col span5 offset-by-one">14</div>

Note: Notice that you need to reduce the number of columns spanned, to make room for the offset!

Try loading and refreshing to see the difference, or check out our fluid-grid-offset.html example (see it running live also). The finished example should look like this:

Note: As an extra exercise, can you implement an offset-by-two class?

Floated grid limitations

When using a system like this you do need to take care that your total widths add up correctly, and that you don’t include elements in a row that span more columns than the row can contain. Due to the way floats work, if the number of grid columns becomes too wide for the grid, the elements on the end will drop down to the next line, breaking the grid.

Also bear in mind that if the content of the elements gets wider than the rows they occupy, it will overflow and look a mess.

The biggest limitation of this system is that it is essentially one dimensional. We are dealing with columns, and spanning elements across columns, but not rows. It is very difficult with these older layout methods to control the height of elements without explicitly setting a height, and this is a very inflexible approach too — it only works if you can guarantee that your content will be a certain height.

Flexbox grids?

If you read our previous article about flexbox, you might think that flexbox is the ideal solution for creating a grid system. There are many flexbox-based grid systems available and flexbox can solve many of the issues that we’ve already discovered when creating our grid above.

However, flexbox was never designed as a grid system and poses a new set of challenges when used as one. As a simple example of this, we can take the same example markup we used above and use the following CSS to style the wrapper, row, and col classes:

body {
  width: 90%;
  max-width: 980px;
  margin: 0 auto;
}

.wrapper {
  padding-right: 2.08333333%;
}


.row {
  display: flex;
}

.col {
  margin-left: 2.08333333%;
  margin-bottom: 1em;
  width: 6.25%;
  flex: 1 1 auto;
  background: rgb(255,150,150);
}

You can try making these replacements in your own example, or look at our flexbox-grid.html example code (see it running live also).

Here we are turning each row into a flex container. With a flexbox-based grid we still need rows in order to allow us to have elements that add up to less than 100%. We set that container to display: flex.

On .col we set the flex property's first value (flex-grow) to 1 so our items can grow, the second value (flex-shrink) to 1 so the items can shrink, and the third value (flex-basis) to auto. As our element has a width set, auto will use that width as the flex-basis value.

On the top line we get twelve neat boxes on the grid and they grow and shrink equally as we change the viewport width. On the next line, however, we only have four items and these also grow and shrink from that 60px basis. With only four of them they can grow a lot more than the items in the row above, the result being that they all occupy the same width on the second row.

To fix this we still need to include our span classes to provide a width that will replace the value used by flex-basis for that element.

They also don’t respect the grid used by the items above because they don’t know anything about it.

Flexbox is one-dimensional by design. It deals with a single dimension, that of a row or a column. We can’t create a strict grid for columns and rows, meaning that if we are to use flexbox for our grid, we still need to calculate percentages as for the floated layout.

In your project you might still choose to use a flexbox ‘grid’ due to the additional alignment and space distribution capabilities flexbox provides over floats. You should, however, be aware that you are still using a tool for something other than what it was designed for. So you may feel like it is making you jump through additional hoops to get the end result you want.

Third party grid systems

Now that we understand the math behind our grid calculations, we are in a good place to look at some of the third party grid systems in common use. If you search for "CSS Grid framework" on the Web, you will find a huge list of options to choose from. Popular frameworks such as Bootstrap and Foundation include a grid system. There are also standalone grid systems, either developed using CSS or using preprocessors.

Let's take a look at one of these standalone systems as it demonstrates common techniques for working with a grid framework. The grid we will be using is part of Skeleton, a simple CSS framework.

To get started visit the Skeleton website, and choose "Download" to download the ZIP file. Unzip this and copy the skeleton.css and normalize.css files into a new directory.

Make a copy of our html-skeleton.html file and save it in the same directory as the skeleton and normalize CSS.

Include the skeleton and normalize CSS in the HTML page, by adding the following to its head:

<link href="normalize.css" rel="stylesheet">
<link href="skeleton.css" rel="stylesheet">

Skeleton includes more than a grid system — it also contains CSS for typography and other page elements that you can use as a starting point. We’ll leave these at the defaults for now, however — it’s the grid we are really interested in here.

Note: Normalize is a really useful little CSS library written by Nicolas Gallagher, which automatically does some useful basic layout fixes and makes default element styling more consistent across browsers.

We will use similar HTML to our earlier example. Add the following into your HTML body:

<div class="container">
  <div class="row">
    <div class="col">1</div>
    <div class="col">2</div>
    <div class="col">3</div>
    <div class="col">4</div>
    <div class="col">5</div>
    <div class="col">6</div>
    <div class="col">7</div>
    <div class="col">8</div>
    <div class="col">9</div>
    <div class="col">10</div>
    <div class="col">11</div>
    <div class="col">12</div>
  </div>
  <div class="row">
    <div class="col">13</div>
    <div class="col">14</div>
    <div class="col">15</div>
    <div class="col">16</div>   
  </div>
</div>


To start using Skeleton we need to give the wrapper <div> a class of container — this is already included in our HTML. This centers the content with a maximum width of 960 pixels. You can see how the boxes now never become wider than 960 pixels.

You can take a look in the skeleton.css file to see the CSS that is used when we apply this class. The <div> is centered using auto left and right margins, and a padding of 20 pixels is applied left and right. Skeleton also sets the box-sizing property to border-box like we did earlier, so the padding and borders of this element will be included in the total width.

.container {
  position: relative;
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 0 20px;
  box-sizing: border-box;
}

Elements can only be part of the grid if they are inside a row, so as with our earlier example we need an additional <div> or other element with a class of row nested between the content <div> and our actual content container <div>s. We've done this already as well.

Now let's lay out the container boxes. Skeleton is based on a 12 column grid. The top line boxes all need classes of one column to make them span one column.

Add these now, as shown in the following snippet:

<div class="container">
  <div class="row">
    <div class="one column">1</div>
    <div class="one column">2</div>        
    <div class="one column">3</div>
    /* and so on */
  </div>
</div>

Next, give the containers on the second row classes explaining the number of columns they should span, like so:

<div class="row">
  <div class="one column">13</div>
  <div class="six columns">14</div>
  <div class="three columns">15</div>
  <div class="two columns">16</div>   
</div>

Try saving your HTML file and loading it in your browser to see the effect.

Note: If you are having trouble getting this example to work, try comparing it to our html-skeleton-finished.html file (see it running live also).

If you look in the skeleton.css file you can see how this works. For example, Skeleton has the following defined to style elements with “three columns” classes added to them.

.three.columns { width: 22%; }

All Skeleton (or any other grid framework) is doing is setting up predefined classes that you can use by adding them to your markup. It’s exactly the same as if you did the work of calculating these percentages yourself.

As you can see, we need to write very little CSS when using Skeleton. It deals with all of the floating for us when we add classes to our markup. It is this ability to hand responsibility for layout over to something else that made using a framework for a grid system a compelling choice! However these days, with CSS Grid Layout, many developers are moving away from these frameworks to use the inbuilt native grid that CSS provides.

Summary

You now understand how various grid systems are created, which will be useful in working with older sites and in understanding the difference between the native grid of CSS Grid Layout and these older systems.

In this module

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