材料设计，自信技术

Question

Do I need to specify the tabindex when using Material Design for a multi-select dropdown so that the keyboard users can navigate easily. I read that there is no need to explicitly mention the tabindex. But, in my case, it is not working without the tabindex.

        <mat-form-field>
        <mat-select>
        <mat-option tabindex="0" title="{{topping?.value}}" *ngFor="let topping of 
        genderList" [value]="topping?.code">{{topping?.value}}</mat-option>
        </mat-select>
        </mat-form-field>

这是我到目前为止所做的一部分代码