我试图在嵌套的* ngFor中获取外部* ngFor的索引 . 附上以下代码：
<div *ngFor="let st of s;let i = index">
<span *ngFor="let indexnumber of i"> </span> //i is the index of above *ngFor
</span>
{{st}}
</div>
我这样做是一个错误： Cannot find a differ supporting object '1' of type 'number'. NgFor only supports binding to Iterables such as Arrays.
我该如何实现这种情况？