bootstrap 範行：

<div class="btn-group">
    <button class="btn">Please Select From List</button>
    <button class="btn dropdown-toggle" data-toggle="dropdown">
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu" role="menu" aria-labelledby
 
="dropdownMenu">
       <li><a tabindex="-1" href="#">Item I</a></li>
       <li><a tabindex="-1" href="#">Item II</a></li>
       <li><a tabindex="-1" href="#">Item III</a></li>
       <li class="divider"></li>
       <li><a
 
 tabindex="-1" href="#">Other</a></li>
    </ul>
</div>

問題是，下拉式 button ，希望點選了 menu item 可以把選擇的專案，更新回顯用的元件的標題裡，官方提供的不會更新button 的title. 解法如下：

As far as i understood your issue is that you want to change the text of the button with the clicking linked text, if so you can try this one: 

 $(function(){

    $(".dropdown-menu li a").click(function(){

      $(".btn:first-child").text($(this).text());
      $(".btn:first-child").val($(this).text());

   });

});

As per your comment:

this doesn’t work for me when I have lists item <li> populated through ajax call.

so you have to delegate the event to the closest static parent with .on() jQuery method:

 $(function(){

    $(".dropdown-menu").on('click', 'li a', function(){
      $(".btn:first-child").text($(this).text());
      $(".btn:first-child").val($(this).text());
   });

});

Here event is delegated to static parent $(".dropdown-menu"), although you can delegate the event to the $(document) too because it is always available.

我服用的 html:

<div class="dropdown">
 <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">
 &nbsp;
 <span class="caret"></span>
 </button>
 <ul class="dropdown-menu" aria-labelledby="dropdownMenu1">
 <li><a href="#">&nbsp;</a></li>
 <li><a href="#">Android</a></li>
 <li><a href="#">iOS</a></li>
 </ul>
</div>

我服用的 javascript:

$(function(){
 $(".dropdown-menu").on('click', 'li a', function(){
 $(".btn:first-child").html($(this).text()+' <span class="caret"></span>');
 });
});

如果有多組 dropdown list 我是使用：

html:

<div class="dropdown">
 <button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown" id="dropdownMenu1">
 &nbsp;
 <span class="caret"></span>
 </button>
 <ul class="dropdown-menu" id="dropdownMenu1Item">
 <li><a href="#">&nbsp;</a></li>
 <li><a href="#">Android</a></li>
 <li><a href="#">iOS</a></li>
 </ul>
</div>

javascript:

$(function(){
 $("#dropdownMenu2Item").on('click', 'li a', function(){
 var selText = $(this).text();
 $("#dropdownMenu2:first-child").html(selText+' <span class="caret"></span>');
 });
});
$(function(){
 $("#dropdownMenu1Item").on('click', 'li a', function(){
 var selText = $(this).text();
 $("#dropdownMenu1:first-child").html(selText+' <span class="caret"></span>');
 });
});