无法用ios ionic2上的dragula拖拽

Question

我使用dragula [ng2-dragula]实现了拖放。它在浏览器中完美运行，但是当我在iphone上运行这个应用程序时，它无法正常工作。

<ion-card>
    <ion-card-content style="white-space: nowrap; overflow: auto;">
      <span *ngFor="let word of codeStream;let i = index">        
        <div *ngIf="word.indexOf('??') != -1 && droppableModels[i].length==0" class="blanks-bag" [dragula]="'option-bag'" [dragulaOptions]="dragulaOptionsNonDragable" [dragulaModel]="droppableModels[i]">

        </div>
        <span *ngIf="word.indexOf('??') != -1 && droppableModels[i][0]">
          {{droppableModels[i][0].text}}
        </span>
        <span *ngIf="word == '\t'">&nbsp;&nbsp;&nbsp;&nbsp;</span>       
        <span *ngIf="word == '\n'"><br style="clear:both;"/></span>
        <span *ngIf="(word.indexOf('??') == -1) && (word != '\t') && (word != '\n')" class="word-bag">{{word}} </span>
      </span>
    </ion-card-content>
  </ion-card>  
  <ion-card *ngIf="fillBlanksObj.options.length > 0">
    <ion-card-header>
      Options
    </ion-card-header>
    <ion-card-content style="white-space: nowrap; overflow: auto;">
      <div class="options-bag" [dragula]="'option-bag'" [dragulaModel]="fillBlanksObj.options">
        <span class="option" *ngFor="let option of fillBlanksObj.options">
          {{option.text}}
        </span>
      </div>
    </ion-card-content>
  </ion-card>

我似乎无法找到针对ios的ng2-dragula的任何未解决的问题，但不确定为什么它不能用于iphone [iphone 6，ios 11.1]。