这个问题分为两部分:

当你不知道模态的确切高度时,你如何将模态垂直地放置在中心? 是否有可能有模态居中,并有溢出:auto在模态体,但只有当模态超过屏幕高度?

我试过用这个:

.modal-dialog {
  height: 80% !important;
  padding-top:10%;
}

.modal-content {
  height: 100% !important;
  overflow:visible;
}

.modal-body {
  height: 80%;
  overflow: auto;
}

当内容远远大于垂直屏幕尺寸时,这给了我所需要的结果,但对于较小的模式内容,这几乎是不可用的。


当前回答

一个简单的方法。为我工作。谢谢rensdenobel:) http://jsfiddle.net/rensdenobel/sRmLV/13/

<style>
.vertical-alignment-helper {
    display:table;
    height: 100%;
    width: 100%;
}
.vertical-align-center {
    /* To center vertically */
    display: table-cell;
    vertical-align: middle;
}
.modal-content {
    /* Bootstrap sets the size of the modal in the modal-dialog class, we need to inherit it */
    width:inherit;
    height:inherit;
    /* To center horizontally */
    margin: 0 auto;
}
</style>
<!-- Button trigger modal -->
<button class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal">Launch demo modal</button>
<!-- Modal -->
<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
    <div class="vertical-alignment-helper">
        <div class="modal-dialog vertical-align-center">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">&times;</span><span class="sr-only">Close</span>

                    </button>
                     <h4 class="modal-title" id="myModalLabel">Modal title</h4>

                </div>
                <div class="modal-body">...</div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
                    <button type="button" class="btn btn-primary">Save changes</button>
                </div>
            </div>
        </div>
    </div>
</div>    

其他回答

试试这样做:

.popup__overlay {
    position: fixed;
    left:  0;
    top:  0;
    width: 100%;
    height: 100%;
    z-index: 999;
    text-align: center
    }
.popup {
    display: inline-block;
    vertical-align: middle
    } 

我写的最普遍的解。动态计算对话框高度。(下一步可能是重新计算窗口大小的对话框的高度。)

JSfiddle: http://jsfiddle.net/8Fvg9/3/

// initialise on document ready
jQuery(document).ready(function ($) {
    'use strict';

    // CENTERED MODALS
    // phase one - store every dialog's height
    $('.modal').each(function () {
        var t = $(this),
            d = t.find('.modal-dialog'),
            fadeClass = (t.is('.fade') ? 'fade' : '');
        // render dialog
        t.removeClass('fade')
            .addClass('invisible')
            .css('display', 'block');
        // read and store dialog height
        d.data('height', d.height());
        // hide dialog again
        t.css('display', '')
            .removeClass('invisible')
            .addClass(fadeClass);
    });
    // phase two - set margin-top on every dialog show
    $('.modal').on('show.bs.modal', function () {
        var t = $(this),
            d = t.find('.modal-dialog'),
            dh = d.data('height'),
            w = $(window).width(),
            h = $(window).height();
        // if it is desktop & dialog is lower than viewport
        // (set your own values)
        if (w > 380 && (dh + 60) < h) {
            d.css('margin-top', Math.round(0.96 * (h - dh) / 2));
        } else {
            d.css('margin-top', '');
        }
    });

});

扩展@Finik的精彩回答,这个修复只适用于非移动设备。我在IE8、Chrome和Firefox 22上进行了测试——它可以处理很长或很短的内容。

.modal {
  text-align: center;
}
@media screen and (min-device-width: 768px) {
  .modal:before {
    display: inline-block;
    vertical-align: middle;
    content: " ";
    height: 100%;
  }
}

.modal-dialog {
  display: inline-block;
  text-align: left;
  vertical-align: middle;
}

我知道有点晚了,但我添加了一个新的答案,这样它就不会迷失在人群中。这是一个跨桌面-移动-浏览器的解决方案,在任何地方都能正常工作。

它只需要将模态对话框包装到模态对话框包装类中,并且需要添加以下代码:

.modal-dialog-wrap {
  display: table;
  table-layout: fixed;
  width: 100%;
  height: 100%;
}

.modal-dialog {
  display: table-cell;
  vertical-align: middle;
  text-align: center;
}

.modal-content {
  display: inline-block;
  text-align: left;
}

对话框从中心开始,在内容较大的情况下,它只是垂直增长,直到出现滚动条。

这里有一把能用的小提琴供你欣赏!

https://jsfiddle.net/v6u82mvu/1/

这是相当老的,并特别要求使用Bootstrap 3的解决方案,但任何人都想知道:从Bootstrap 4有一个内置的解决方案称为.modal-dialog-centered。问题是:https://github.com/twbs/bootstrap/issues/23638

所以使用v4,你只需要添加.modal-dialog- centric到.modal-dialog来垂直居中模态:

<!-- Button trigger modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModalCenter">
  Launch demo modal
</button>

<!-- Modal -->
<div class="modal fade" id="exampleModalCenter" tabindex="-1" role="dialog" aria-labelledby="exampleModalCenterTitle" aria-hidden="true">
  <div class="modal-dialog modal-dialog-centered" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="exampleModalCenterTitle">Modal title</h5>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">&times;</span>
        </button>
      </div>
      <div class="modal-body">
        ...
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div>
  </div>
</div>

Demo