嵌套* ngFor引导程序崩溃

Question

几个小时我试图找出如何使其工作。
到处搜索并找不到写入示例。
我使用j作为索引的第二个块不会扩展？

这里是我的代码..

<div class="col-xs-2"> 
    <div class="list-group list-group-root well"> 
     <span *ngFor="let region of locations; let i = index"> 
      <a class="list-group-item" 
       data-toggle="collapse" 
       [attr.data-target]="'#' + i" 
       (click)="centerOn(region.name, region)"> 
       <i class="glyphicon glyphicon-chevron-right"></i>{{ region.name }} 
      </a> 
      <div class="list-group collapse" [attr.id]="i"> 
       <span *ngFor="let city of region.cities; let j = index"> 
        <a class="list-group-item" 
         data-toggle="collapse" 
         [attr.data-target]="'#' + j" 
         (click)="centerOn(city.name, city)"> 
         <i class="glyphicon glyphicon-chevron-right"></i>{{ city.name }} 
        </a> 
        <div class="list-group collapse" [attr.id]="j"> 
         <span *ngFor="let cityArea of city.areas"> 
          <a class="list-group-item" 
           data-toggle="collapse" 
           (click)="centerOn(cityArea.name, cityArea)"> 
           {{ cityArea.name }} 
          </a> 
        </span> 
       </div> 
      </span> 
     </div> 
    </span> 
</div> 

Answer 1

配有专业的工程师咨询后，我得到它的工作！
我添加前缀到j指数+ I指数在这两个地方，瞧:)

[attr.data-target]="'#' + 'prefix' + j + i"  
[attr.id]=" 'prefix' + j + i"  

好运！