在我的情况下，我有两个情态动词同样的问题，所有都解决了使用:

$('.select2').each(function() { 
    $(this).select2({ dropdownParent: $(this).parent()});
})

正如在项目问题#41中，一个用户说。

要使用bootstrap 4.0与服务器端(ajax或json数据内联)，你需要添加所有这些:

$.fn.modal.Constructor.prototype._enforceFocus = function() {};

然后当modal打开时，创建select2:

  // when modal is open
  $('.modal').on('shown.bs.modal', function () {
            $('select').select2({
                  // ....
            });
  });

为了更好地理解tabindex元素是如何工作的，完成公认的回答:

The tabindex global attribute is an integer indicating if the element can take input focus (is focusable), if it should participate to sequential keyboard navigation, and if so, at what position. It can take several values:   -a negative value means that the element should be focusable, but should not be reachable via sequential keyboard navigation;   -0 means that the element should be focusable and reachable via sequential keyboard navigation, but its relative order is defined by the platform convention;   -a positive value means should be focusable and reachable via sequential keyboard navigation; its relative order is defined by the value of the attribute: the sequential follow the increasing number of the tabindex. If several elements share the same tabindex, their relative order follows their relative position in the document.

来自:Mozilla开发人员网络

在我的项目中，我通过重载select2函数来解决这个问题。现在它将检查是否没有dropdownParent，以及函数是否在父元素类型为div.modal的元素上调用。如果是，它将添加该模态作为下拉列表的父类。

这样，就不必在每次创建select2-input框时都指定它。

(function(){
    var oldSelect2 = jQuery.fn.select2;
    jQuery.fn.select2 = function() {
        const modalParent = jQuery(this).parents('div.modal').first();
        if (arguments.length === 0 && modalParent.length > 0) {
            arguments = [{dropdownParent: modalParent}];
        } else if (arguments.length === 1
                    && typeof arguments[0] === 'object'
                    && typeof arguments[0].dropdownParent === 'undefined'
                    && modalParent.length > 0) {
            arguments[0].dropdownParent = modalParent;
        }
        return oldSelect2.apply(this,arguments);
    };
    // Copy all properties of the old function to the new
    for (var key in oldSelect2) {
        jQuery.fn.select2[key] = oldSelect2[key];
    }
})();

在我的情况下，我这样做，它工作。我使用bundle来加载它，在这种情况下，它为我工作

 $(document).on('select2:select', '#Id_Producto', function (evt) {
   // Here your code...
  });

如果你使用jquery移动弹出窗口，你必须重写_handleDocumentFocusIn函数:

.mobile.popup.prototype美元。_handleDocumentFocusIn =函数(e) { If ($(e.c target).close ('.select2-dropdown').length)返回true; ｝