第 31 章 项目实战-PC端固定布局[2]

学习要点：

1.大纲算法

2.section和div

3.结构分析

主讲教师：李炎恢

本章主要开始使用学习用HTML5和CSS3来构建Web页面，第一个项目采用PC端 固定布局来实现。

一．大纲算法 

在HTML5中有一个很重要的概念，叫做HTML5大纲算法(HTML5Outliner)，它的用途是为用户提供一份页面的信息结构目录。比如我们经常使用的手册就是一个非常好的大纲 结构：

合理的使用HTML5元素标签，可以生成一个非常清晰的文档大纲，我们可以通过各种 工具去查看当前页面，比如谷歌和火狐的插件可以查看当前的HTML5大纲。这里我们推荐 使用一个服务器端的测试工具：HTML 5 Outliner，网址如下：

测试工具：https://gsnedders.html5.org/outliner/

这个工具可以上传本地html文件，也可以填写URL，或者直接在多行文本框上编写HTML5代码均可了解大纲。

通过我们将上一节课的代码编写，发现这个页面的大纲非常的难看，出现三个Untitled Section，这个意思表示页面此处缺少大纲标题，不规范。如果你的页面在这里测试，大纲都比较清晰，那么HTML5页面是比较规范的。

//大纲目录结构

1.UntitledSection

1.UntitledSection

1.瓢城旅行社

2.UntitledSection

二．section和div 

首先，我们暂不探讨怎么让html5页面大纲合乎规范。先探讨一下section和div的区别。

div元素在html5之前就是非常常用的标签，它本身没有任何语义，用来页面布局和 CSS样式以及JS调用。那么，div的用途已经说的很清楚了：

1.如果是页面布局，且不是header、footer之类的专属区域，都应该使用div；

2.如果只是单纯的对一个端内容进行CSS样式定义，那么也应该使用div;

3.如果想对一段内容进行JS控制，那么也应该使用div。

html5中，section并不是用来取代div的。在基础课程中已经简单的了解过，它是具有语义的文档标签。表示一段文档中的章节，比如包含一个标题和一个段落，而大纲规范 中，至少要包含一个标题。

//section至少需要一个h1~h6

<section>
    <h2>Bootstrap</h2>
    <p>Bootstrap是一款html5开源框架</p>
</section>

通过上诉说明，我们对于下方的section标签，增加一个h2即可实现大纲要求。最终 大纲变成如下结构：

//大纲目录结构

1.UntitledSection

1.UntitledSection

1.瓢城旅行社

2.波特四抓

那么发现最后一个UntitledSection已经拥有了标题，已经符合规范。对于前面还 有两个，待会儿再说。现在再探讨一个问题，既然div用于没有任何语义的布局和样式定  义，那么我们就需要探讨一下如下代码用div还是section。

//这里改用section还是div呢？

<section class="center">
    <h1 class="logo"> 瓢城旅行社</h1>
    <ul class="link">
        <li class="active">
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" > 首页</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" > 旅游资讯</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" > 机票订购</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" > 风景欣赏</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >公司简介</a>
        </li>
    </ul>
</section>

从结构上来看，section需要包含至少一个h1~h6，这里是符合的。但容易混淆的 部分是，section是某个区域章节的标题，h1其实是整个网站的标题。而ul部分是导航超 链接，严格来讲，也不算章节的内容。最重要的是这块的section用于的布局样式定义， 所以我个人认为这里使用div更加妥当一些。

注：section本身使用频率并不是很高，而section并不是代替div的元素。

//比较合理的做法

<div class="center">
    <h1 class="logo">瓢城旅行社</h1>
    <ul class="link">
        <li class="active">
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >首页</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >旅游资讯</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >机票订购</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >风景欣赏</a>
        </li>
        <li>
            <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >公司简介</a>
        </li>
    </ul>
</div>

这里大纲进行了一个很有趣的变化，如下：

//改变后的大纲

1.UntitledSection

1.瓢城旅行社

2.波特四抓

通过目前的大纲，我们可以了解到，还剩一个标题就可以实现完美大纲。这个剩下的标 题是哪个元素下的呢？答案是：body元素。我们只要在body元素下创建一个h1，写上标 题名称，即可。

//增加body标题，解决大纲问题

<body>
    <h1>Body大标题</h1>
     ...
</body>

虽然在body增加标题解决了大纲问题，但问题是我们本身页面设计根本不需要在body 创建一个h1啊。难道创建后，再隐藏这种多此一举的方法吗？这个问题，稍后再看，先再 探讨一下头部的结构问题。

三．结构分析 

首先，探讨一下nav元素。这个元素本质上是用来存放一组作为导航的链接，比如ul。

我们第一节课，把整个头部全部存放进去，显得不是特别合理，所以，最好在ul的外围。  而LOGO+导航，我们可以理解为header头部，所以，最终改写成如下结构：

//头部元素换成了header，nav元素只包含ul

<header id="header">
    <div class="center">
        <h1 class="logo">瓢城旅行社</h1>
        <nav class="link">
            <ul>
                <li class="active">
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >首页</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >旅游资讯</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >机票订购</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >风景欣赏</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >公司简介</a>
                </li>
            </ul>
        </nav>
    </div>
</header>

在去掉<body><h1>…</h1></body>的情况下，我们发现，这种结构的主标题大纲居 然是：瓢城旅行社。而<nav>下则又出现一个UntitledSection，由此可得到几个结论：

1.header元素不需要强制标题h1~h6，如果有标题，算body的。这样主大纲标题就有了；
2.section和nav元素大纲要求有标题h1 ~ h6，但section必须有才规范，而nav如果没有标题，也是合理的。当然，添加上标题会让大纲更加好看，页面中可以隐藏。

//最终格式如下：

<header id="nav">
    <div class="center">
        <h1 class="logo">瓢城旅行社</h1>
        <nav class="link">
            <h2 class="none">网站导航</h2>
            <ul>
                <li class="active">
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >首页</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >旅游资讯</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >机票订购</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >风景欣赏</a>
                </li>
                <li>
                    <a href="###" rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow"  rel="external nofollow" >公司简介</a>
                </li>
            </ul>
        </nav>
    </div>
</header>

根据改变的元素内容，适当更改一下CSS即可。