如何在angular ui sortable callback中等待确认对话框

Question

我使用angular ui sortable来在列表之间拖放项目。我希望能够做的是（在某些拖放条件下）有一个确认对话框，如果用户取消对话框，则将列表恢复到原始状态。我可以在更新事件中使用ui.item.sortable.cancel()方法，但如果我使用返回promise的模式，我无法弄清楚如何在取消时恢复列表。这是我在控制器中的内容（modalService是一个bootstrap $ uibModal）：

$scope.sortableOptions =
        handle: ' > span > span > .task-drag-icon',
        connectWith: ".task-subset"
        placeholder: "sortable-placeholder",
        forcePlaceholderSize: true,
        update: (e, ui) ->
          if ui.item.sortable.sourceModel == ui.item.sortable.droptargetModel #sort was within the same list
            #some other logic here.....
          else
            droptarget_element = ui.item.sortable.droptarget

            if droptarget_element.attr('ng-model') == "task.subTasks"
              #need the user to confirm here if they really want to do this drag/drop
              modalOptions =
                closeButtonText: 'Cancel'
                actionButtonText: 'Make SubTask'
                headerText: 'Make SubTask?'
                bodyText: 'This action will remove any existing task groups as it will become a child task. Is this OK?'
              modalService.showModal({}, modalOptions).then (result) ->
                  console.log "accpted"
                , () ->
                  console.log "cancelled"
                  #need to call ui.item.sortable.cancel() here, but I cant because the update callback has finished already!!!!

              console.log "finished - gets to here immediately as modalService is asyncronous"

          return

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