Navigation bar that Bootstrap must learn every day_javascript skills-JS Tutorial-php.cn

1. Navigation bar

The difference between the navigation bar (navbar) and the navigation (nav) introduced in the previous section is just one word, with the addition of the word "bar". In fact, they are still obviously different in the Bootstrap framework. There is a background color in the navigation bar (navbar) (the display is more prominent), and the navigation bar can be a pure link (similar to navigation), a form, or a combination of form and navigation. In this section, we will discuss the use of navigation bars in the Bootstrap framework.

The navigation bar, like the navigation, is an independent component in the Bootstrap framework, so you can also use different versions according to your needs:

LESS version: corresponding source file navbar.less
Sass version: corresponding source file _navbar.scss
Compiled version: Check lines 3642 to 4111 of the bootstrap.css file (note that the Bootstrap version mentioned here is 3.1.1, and the locations of other versions are inconsistent).

2. Basic navigation bar

In the Bootstrap box, the appearance of the navigation bar and navigation is not much different, but in actual use the navigation bar is much more complicated than the navigation. Let’s first look at the most basic one of the navigation bars—the basic navigation bar.

1), usage:

When making a basic navigation bar, there are mainly the following steps:

Step one: First, add the class name “navbar-nav” based on the list of navigation (
```
<div class="navbar navbar-default" role="navigation">
 <ul class="nav navbar-nav">
 <li class="active"><a href="##">网站首页</a></li>
 <li><a href="##">系列教程</a></li>
 <li><a href="##">名师介绍</a></li>
 <li><a href="##">成功案例</a></li>
 <li><a href="##">关于我们</a></li>
 </ul>
</div>
```
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The main function of the ".navbar" style is to set effects such as left and right padding and rounded corners, but it does not have any settings related to color styles. Its main source code is as follows:

/Source code view bootstrap.css file line 3642~line 3647/
```
.navbar {
 position: relative;
 min-height: 50px;
 margin-bottom: 20px;
 border: 1px solid transparent;
}
```
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2), principle analysis:

The color of the navigation bar is controlled through ".navbar-default":

/Source code view bootstrap.css file line 3940~line 3943/
```
.navbar-default {
 background-color: #f8f8f8;
 border-color: #e7e7e7;
}
```
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The navbar-nav style re-adjusts the floating and inner and outer margins of menu items based on navigation.nav. It also does not include color and other style settings. For the source code, please view lines 3785 to 3830 of the bootstrap.css file. We will extract the code and put it into bootstrap.css on the right.

The colors and other styles are implemented together with the parent container "navbar-default":

/For the source code, please view lines 3955~3974 of the bootstrap.css file/
```
.navbar-default .navbar-nav> li > a {
 color: #777;
}
.navbar-default .navbar-nav> li >a:hover,
.navbar-default .navbar-nav> li >a:focus {
 color: #333;
 background-color: transparent;
}
.navbar-default .navbar-nav> .active > a,
.navbar-default .navbar-nav> .active >a:hover,
.navbar-default .navbar-nav> .active >a:focus {
 color: #555;
 background-color: #e7e7e7;
}
.navbar-default .navbar-nav> .disabled > a,
.navbar-default .navbar-nav> .disabled >a:hover,
.navbar-default .navbar-nav> .disabled >a:focus {
 color: #ccc;
 background-color: transparent;
}
```
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3. Add a title, secondary menu and status to the navigation bar

1), add navigation bar title

In web page production, there is often a title in front of the menu (the text size is slightly larger than other text). In fact, the Bootstrap framework has also considered this aspect for everyone. It uses "navbar-header" and " navbar-brand" to achieve.
```
<div class="navbar navbar-default" role="navigation">
 　<div class="navbar-header">
 　 <a href="##" class="navbar-brand">慕课网</a>
 　</div>
 <ul class="nav navbar-nav">
 <li class="active"><a href="##">网站首页</a></li>
 <li><a href="##">系列教程</a></li>
 <li><a href="##">名师介绍</a></li>
 <li><a href="##">成功案例</a></li>
 <li><a href="##">关于我们</a></li>
 </ul>
</div>
```
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2), principle analysis:

This function mainly serves as a reminder function. Of course, if improved, it can be used as a logo (not to be elaborated here). The style mainly increases the font setting and sets the maximum width:

/Source code view bootstrap.css file line 3739~line 3755/
```
.navbar-brand {
 float: left;
 height: 50px;
 padding: 15px 15px;
 font-size: 18px;
 line-height: 20px;
}
.navbar-brand:hover,
.navbar-brand:focus {
 text-decoration: none;
}
@media (min-width: 768px) {
 .navbar> .container .navbar-brand,
 .navbar> .container-fluid .navbar-brand {
 margin-left: -15px;
 }
}
```
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Also under the default navigation bar (navbar-default), the navbar-brand is also colored:

/For the source code, please view lines 3947~3951 of the bootstrap.css file/
```
.navbar-default .navbar-brand {
color: #777;
}
.navbar-default .navbar-brand:hover,
.navbar-default .navbar-brand:focus {
color: #5e5e5e;
background-color: transparent;
}
```
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3), navigation bar status, secondary menu

Similarly, the basic navigation bar provides menus with current status, disabled status, suspended status and other effects, and can also have a navigation bar with secondary menus.
```
<div class="navbar navbar-default" role="navigation">
 　<div class="navbar-header">
 　 <a href="##" class="navbar-brand">慕课网</a>
 　</div>
 <ul class="nav navbar-nav">
 <li class="active"><a href="##">网站首页</a></li>
 <li class="dropdown">
  <a href="##" data-toggle="dropdown" class="dropdown-toggle">系列教程<span class="caret"></span></a>
  <ul class="dropdown-menu">
  <li><a href="##">CSS3</a></li>
  <li><a href="##">JavaScript</a></li>
  <li class="disabled"><a href="##">PHP</a></li>
  </ul>
 </li>
 <li><a href="##">名师介绍</a></li>
 <li><a href="##">成功案例</a></li>
 <li><a href="##">关于我们</a></li>
 </ul>
</div>
```
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效果图如下：

4、带表单的导航条

有的导航条中会带有搜索表单，比如新浪微博的导航条：

在Bootstrap框架中提供了一个“navbar-form”，使用方法很简单，在navbar容器中放置一个带有navbar-form类名的表单。
```
<div class="navbar navbar-default" role="navigation">
 　<div class="navbar-header">
 　 <a href="##" class="navbar-brand">慕课网</a>
 　</div>
 <ul class="nav navbar-nav">
 <li class="active"><a href="##">网站首页</a></li>
 <li class="dropdown">
  <a href="##" data-toggle="dropdown" class="dropdown-toggle">系列教程<span class="caret"></span></a>
  <ul class="dropdown-menu">
  <li><a href="##">CSS3</a></li>
  <li><a href="##">JavaScript</a></li>
  <li class="disabled"><a href="##">PHP</a></li>
  </ul>
 </li>
 <li><a href="##">名师介绍</a></li>
 <li><a href="##">成功案例</a></li>
 <li><a href="##">关于我们</a></li>
 </ul>
 <form action="##" class="navbar-form navbar-left" rol="search">
 <div class="form-group">
  <input type="text" class="form-control" placeholder="请输入关键词" />
 </div>
 <button type="submit" class="btn btn-default">搜索</button>
 </form>
</div>
```
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实现导航条+表单的样式代码源码请查看bootstrap.css文件第3839行～第3904行.

在上面的示例中，大家看到了“navbar-left”让表单左浮动，更好实现对齐。在Bootstrap框架中，还提供了“navbar-right”样式，让元素在导航条靠右对齐。

/源码请查看bootstrap.css文件第3831行～第3838行/
```
@media (min-width: 768px) {
 .navbar-left {
 float: left !important;
}
.navbar-right {
 float: right !important;
 }
}
```
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注意：这里有一个条件，只有当浏览器视窗宽度大于768px生效。

5、导航条中的按钮、文本和链接

Bootstrap框架的导航条中除了使用navbar-brand中的a元素和navbar-nav的ul和navbar-form之外，还可以使用其他元素。框架提供了三种其他样式：
- 1、导航条中的按钮navbar-btn
- 2、导航条中的文本navbar-text
- 3、导航条中的普通链接navbar-link
但这三种样式在框架中使用时受到一定的限制，需要和navbar-brand、navbar-nav配合起来使用。而且对数量也有一定的限制，一般情况在使用一到两个不会有问题，超过两个就会有问题。

先来看看这三种样式对应的源码：

/源码请查看bootstrap.css文件第3914行～第3939行/
```
.navbar-btn {
margin-top: 8px;
margin-bottom: 8px;
}
.navbar-btn.btn-sm {
margin-top: 10px;
margin-bottom: 10px;
}
.navbar-btn.btn-xs {
margin-top: 14px;
margin-bottom: 14px;
}
.navbar-text {
margin-top: 15px;
margin-bottom: 15px;
}
@media (min-width: 768px) {
.navbar-text {
float: left;
margin-right: 15px;
margin-left: 15px;
 }
.navbar-text.navbar-right:last-child {
margin-right: 0;
 }

}
/bootstrap.css文件第3952行～第3954行/

.navbar-default .navbar-text {
 color: #777;
}

/bootstrap.css文件第4035行～第4037行/

.navbar-inverse .navbar-text {
color: #999;
}

/boostrap.css文件第4017行～第4022行/

.navbar-default .navbar-link {
color: #777;
}
.navbar-default .navbar-link:hover {
color: #333;
}

/bootstrap.css文件第4106行～第4111行/

.navbar-inverse .navbar-link {
color: #999;
}
.navbar-inverse .navbar-link:hover {
color: #fff;
}
```
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navbar-btn和navbar-link在上一小节已经讲过，现在我们来看一下navbar-text的一个简单应用
```
<div class="navbar navbar-default" role="navigation">
 　<div class="navbar-header">
 　 <a href="##" class="navbar-brand">慕课网</a>
 　</div>
 <ul class="nav navbar-nav">
 <li><a href="##" class="navbar-text">Navbar Text</a></li>
 <li><a href="##" class="navbar-text">Navbar Text</a></li>
 <li><a href="##" class="navbar-text">Navbar Text</a></li>
 </ul>
</div>
```
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在结果窗口中查看效果，可以看出明显的存在问题.

通过浏览器调试工具，可以看到a标签有margin-top和margin-bottom的值为15px，欲将其对齐，我们将上面的结构做一定的调整. 将