title: How to get mat-checkbox checked value if used in ngFor
body: <p>I'm trying to get all checkboxes which are checked and perform some function on them.</p>
  
  <pre><code>&lt;div class="outerdiv" *ngFor="let item of items"&gt;
  &lt;mat-checkbox&gt;Hello&lt;/mat-checkbox&gt;
  &lt;div&gt;
  
  &lt;button (click)="filterSelectedItems()"&gt;&lt;/button&gt;
  
  filterSelectedItems(){
  let outerdiv = this.element.nativeElement.querySelectorAll('.outerdiv');
   for(let i = 0; i &lt; outerdiv.length; i++){
        let option = outerdiv[i].querySelector('mat-checkbox');
        if(option.checked){
          this.filterItem+=option.innerText;
        }
  }
  </code></pre>