下拉菜单上的bootstrap 3箭头

In bootstrap 2 the dropdown menu had an upwards arrow as it can be seen here (i am not talking about the carret). Now using bootstrap 3 or latest git this arrow doesn't exist in my simple example bellow nor in the examples on the bootstrap homepage.

在bootstrap 2中，下拉菜单中有一个向上的箭头，因为它可以在这里看到（我不是在谈论carret）。现在使用bootstrap 3或最新的git，这个箭头不存在于我的简单示例中，也不存在于bootstrap主页的示例中。

How can I add this arrow again using bootstrap 3?

如何使用bootstrap 3再次添加此箭头？

  <li class="dropdown">
    <a href="#" class="dropdown-toggle" data-toggle="dropdown">
      Menu
      <b class="caret"></b>
    </a>
    <ul class="dropdown-menu">
      <li><a href="#">a</a></li>
      <li><a href="#">b</a></li>
      <li><a href="#">c</a></li>
    </ul>
  </li>

PS:To be precise the picture can be seen in another * article.

PS：准确地说，图片可以在另一个*文章中看到。

4 个解决方案

#1

150

You need to add :after and :before css rules to your dropdown-menu. These rules are taken from Bootstrap 2, and are what draw the triangle above the dropdown.

您需要在下拉菜单中添加：after和：之前的css规则。这些规则取自Bootstrap 2，并且是在下拉列表上方绘制三角形的内容。

JSFiddle DEMO

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 9px;
  display: inline-block;
  border-right: 7px solid transparent;
  border-bottom: 7px solid #ccc;
  border-left: 7px solid transparent;
  border-bottom-color: rgba(0, 0, 0, 0.2);
  content: '';
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 10px;
  display: inline-block;
  border-right: 6px solid transparent;
  border-bottom: 6px solid #ffffff;
  border-left: 6px solid transparent;
  content: '';
}

Confused how? See here for an animation that explains css triangles

困惑如何？请参阅此处获取解释css三角形的动画

#2

Just to follow up on this - if you want the arrow to position itself correctly (like when using it on a navbar element that is right-aligned, you need the following additional CSS to ensure the arrow is right-aligned:

只是为了跟进这个 - 如果你想让箭头正确定位（就像在右对齐的导航栏元素上使用它一样，你需要以下额外的CSS来确保箭头是右对齐的：

.navbar .navbar-right > li > .dropdown-menu:before,
.navbar .nav > li > .dropdown-menu.navbar-right:before {
    right: 12px; left: auto;
}

.navbar .navbar-right > li > .dropdown-menu:after,
.navbar .nav > li > .dropdown-menu.navbar-right:after {
    right: 13px; left: auto;
}

Note the "navbar-right" - that was introduced in BS3 instead of pull-right for navbars.

注意“navbar-right” - 在BS3中引入而不是用于导航栏的右拉。

#3

The CSS that Alexander Mistakidis provided is correct. Which is to say, it creates the arrow atop the dropdown menu in Bootstrap. In order to position it correctly in a responsive view (@user2993108), you can change the left attribute for each of the class selectors (.dropdown-menu:before,.dropdown-menu:after) at different media queries or breakpoints.

Alexander Mistakidis提供的CSS是正确的。也就是说，它会在Bootstrap的下拉菜单中创建箭头。为了在响应式视图中正确定位（@ user2993108），您可以在不同的媒体查询或断点处更改每个类选择器（.dropdown-menu：before，.dropdown-menu：after）的左侧属性。

For example...

例如...

@media (max-width: 400px) {

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 30px; /* change for positioning */
  ...
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 31px; /* change for positioning */
  ...
}

}

@media (max-width: 767px) and (min-width: 401px) {

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 38px; /* change for positioning */
  ...
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 39px; /* change for positioning */
  ...
}

}

and so on...

等等...

#4

This builds on the work by Alexander Mistakidis and Joyrex to support optional arrows and dropup menus. In my case I did not want to have an arrow on all of the dropdown menus, only some.

这是基于Alexander Mistakidis和Joyrex的工作，以支持可选的箭头和下拉菜单。在我的情况下，我不想在所有下拉菜单上都有箭头，只有一些。

With this, you add the arrow class to the dropdown-menu element to get the arrow. If Bootstrap is positioning the dropdown/dropup to the left, also add arrow-right to shift the arrow to the other side.

这样，您可以将箭头类添加到下拉菜单元素以获取箭头。如果Bootstrap将下拉/下拉定位到左侧，也可以向右添加箭头以将箭头移动到另一侧。

// add an arrow to the dropdown menus
.dropdown-menu.arrow:before {
  position: absolute;
  left: 9px;
  display: inline-block;
  border-right: 7px solid transparent;
  border-left: 7px solid transparent;
  content: '';
}
.dropdown-menu.arrow:after {
  position: absolute;
  left: 10px;
  display: inline-block;
  border-right: 6px solid transparent;
  border-left: 6px solid transparent;
  content: '';
}

// postion at the top for a 'down' menu
.dropdown .dropdown-menu.arrow:before {
  top: -7px;
  border-bottom: 7px solid #ccc;
  border-bottom-color: rgba(0, 0, 0, 0.2);
}
.dropdown .dropdown-menu.arrow:after {
  top: -6px;
  border-bottom: 6px solid #ffffff;
}

// postion at the bottom for an 'up' menu
.dropup .dropdown-menu.arrow:before {
  bottom: -7px;
  border-top: 7px solid #ccc;
  border-top-color: rgba(0, 0, 0, 0.2);
}
.dropup .dropdown-menu.arrow:after {
  bottom: -6px;
  border-top: 6px solid #ffffff;
}

// support to move the arrow to the right-hand-side
.dropdown-menu.arrow.arrow-right:before,
.dropup .dropdown-menu.arrow.arrow-right:before {
  right: 15px;
  left: auto;
}
.dropdown-menu.arrow.arrow-right:after,
.dropup .dropdown-menu.arrow.arrow-right:after {
  right: 16px;
  left: auto;
}

#1

150