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

从这里找到了完美的解决方案

$(function() {
    function reposition() {
        var modal = $(this),
            dialog = modal.find('.modal-dialog');
        modal.css('display', 'block');

        // Dividing by two centers the modal exactly, but dividing by three 
        // or four works better for larger screens.
        dialog.css("margin-top", Math.max(0, ($(window).height() - dialog.height()) / 2));
    }
    // Reposition when a modal is shown
    $('.modal').on('show.bs.modal', reposition);
    // Reposition when the window is resized
    $(window).on('resize', function() {
        $('.modal:visible').each(reposition);
    });
});

其他回答

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;
}

还有另一种解决方案,它将为窗口上的每个可见模态设置有效的位置。调整大小事件和show.bs.modal:

(function ($) {
    "use strict";
    function centerModal() {
        $(this).css('display', 'block');
        var $dialog  = $(this).find(".modal-dialog"),
            offset       = ($(window).height() - $dialog.height()) / 2,
            bottomMargin = parseInt($dialog.css('marginBottom'), 10);

        // Make sure you don't hide the top part of the modal w/ a negative margin if it's longer than the screen height, and keep the margin equal to the bottom margin of the modal
        if(offset < bottomMargin) offset = bottomMargin;
        $dialog.css("margin-top", offset);
    }

    $(document).on('show.bs.modal', '.modal', centerModal);
    $(window).on("resize", function () {
        $('.modal:visible').each(centerModal);

    });
})(jQuery);

我的解决方案

.modal-dialog-center {
    margin-top: 25%;
}

    <div id="waitForm" class="modal">
        <div class="modal-dialog modal-dialog-center">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
                    <h4 id="headerBlock" class="modal-title"></h4>
                </div>
                <div class="modal-body">
                    <span id="bodyBlock"></span>
                    <br/>
                    <p style="text-align: center">
                        <img src="@Url.Content("~/Content/images/progress-loader.gif")" alt="progress"/>
                    </p>   
                </div>
            </div>
        </div>
    </div>

如果您可以使用flexbox,那么这应该有助于解决问题。

.modal-dialog {
  height: 100%;
  width: 100%;
  display: flex;
  align-items: center;
}

.modal-content {
  margin: 0 auto;
}

在我的例子中,我所做的就是在css中设置顶部,知道模态的高度

<div id="myModal" class="modal fade">…< / div >

在我的CSS中

#myModal{
    height: 400px;
    top: calc(50% - 200px) !important;
}