title: Mat-Tooltips in *ngFor
body: <p>How can dynamically show and hide material design tooltips?
  I have component which displays tooltips int *ngFor</p>
  
  <pre><code>&lt;div *ngFor="let item of items" fxLayout="row"&gt;
          &lt;mat-form-field matTooltip="{{item.comment}}"&gt;
            &lt;input matInput&gt;
          &lt;/mat-form-field&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I have button, to handle show/hide toolbars on change, but how to show and hide these toolbars?</p>
  
  <p>In doc there is example using one toolbar:</p>
  
  <pre><code> &lt;button mat-raised-button (click)="tooltip.show()"&gt; Show tooltip &lt;/button&gt;
  
  &lt;span matTooltip="This is the tooltip message" #tooltip="matTooltip"&gt;
    I have a tooltip
  &lt;/span&gt;
  </code></pre>
  
  <p>This is easy, but how to deal with multiple tooltips from *ngFor?</p>