Bootstrap 4：仅在导航选项卡处于活动状态时显示元素

Question

我正在制作需要仅在活动元素上显示元素的导航选项卡。就我而言，它是指向内容的白色箭头。当您单击另一个选项卡时，如何使其消失？或者，我怎样才能将它移动到该选项卡，以便它指向它的内容？

这是我的代码大纲：

.arrow-down {
    position: absolute;
    width: 0; 
    height: 0; 
    border-left: 15px solid transparent;
    border-right: 15px solid transparent;
    border-top: 15px solid white;
  margin-left: 20px;
}
.nav-tabs {
    background-color: black;
}
.tab-content {
  background-color: #ccc
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js" integrity="sha384-A7FZj7v+d/sdmMqp/nOQwliLvUsJfDHW+k9Omg/a/EheAdgtzNs3hpfag6Ed950n" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js" integrity="sha384-DztdAPBWPRXSA/3eYEEUWrWCy7G5KFbe8fFjk5JAIxUYHKkDx6Qin1DkWx51bBrb" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js" integrity="sha384-vBWWzlZJ8ea9aCX4pEW3rVHjgjt7zpkNpZk+02D9phzyeVkE+jo0ieGizqPLForn" crossorigin="anonymous"></script>


<ul class="nav nav-tabs" role="tablist">
  <li class="nav-item">
    <a class="nav-link active" data-toggle="tab" href="#home" role="tab">Home</a>
    <div class="arrow-down"></div>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#profile" role="tab">Profile</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#messages" role="tab">Messages</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#settings" role="tab">Settings</a>
  </li>
</ul>

<div class="tab-content">
  <div class="tab-pane active" id="home" role="tabpanel">...</div>
  <div class="tab-pane" id="profile" role="tabpanel">...</div>
  <div class="tab-pane" id="messages" role="tabpanel">...</div>
  <div class="tab-pane" id="settings" role="tabpanel">...</div>
</div>

Answer 1

添加一个类以显示箭头，然后将点击事件添加到所有菜单，删除前一个箭头并添加到当前选项卡。

.active-arrow {
  display: block;
}

要使箭头居中，您可以使用 flexbox，并将 margin-top 添加到每个箭头以使其正确定位。

.nav-item {
  display: flex;
  align-items: center;
  justify-content: center;
}

$('ul a.nav-link').on('click', function(e) {
  $('.arrow-down').removeClass('active-arrow');
  $(this).next('.arrow-down').addClass('active-arrow');
})

.arrow-down {
  position: absolute;
  width: 0;
  height: 0;
  border-left: 15px solid transparent;
  border-right: 15px solid transparent;
  border-top: 15px solid white;
  display: none;
  margin-top: 28px;
}

.nav-item {
  display: flex;
  align-items: center;
  justify-content: center;
}

.active-arrow {
  display: block;
}

.nav-tabs {
  background-color: black;
}

.tab-content {
  background-color: #ccc
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js" integrity="sha384-A7FZj7v+d/sdmMqp/nOQwliLvUsJfDHW+k9Omg/a/EheAdgtzNs3hpfag6Ed950n" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js" integrity="sha384-DztdAPBWPRXSA/3eYEEUWrWCy7G5KFbe8fFjk5JAIxUYHKkDx6Qin1DkWx51bBrb" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js" integrity="sha384-vBWWzlZJ8ea9aCX4pEW3rVHjgjt7zpkNpZk+02D9phzyeVkE+jo0ieGizqPLForn" crossorigin="anonymous"></script>


<ul class="nav nav-tabs" role="tablist">
  <li class="nav-item">
    <a class="nav-link active" data-toggle="tab" href="#home" role="tab">Home</a>
    <div class="arrow-down active-arrow"></div>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#profile" role="tab">Profile</a>
    <div class="arrow-down"></div>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#messages" role="tab">Messages</a>
    <div class="arrow-down"></div>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#settings" role="tab">Settings</a>
    <div class="arrow-down"></div>
  </li>
</ul>

<div class="tab-content">
  <div class="tab-pane active" id="home" role="tabpanel">1</div>
  <div class="tab-pane" id="profile" role="tabpanel">2</div>
  <div class="tab-pane" id="messages" role="tabpanel">3</div>
  <div class="tab-pane" id="settings" role="tabpanel">4</div>
</div>