title: How to set values in formarray
body: <p>I have a form array that is dynamically set after getting data from a service with initial values being false.</p>
  <pre><code>constructor(){
      this.form = this.fb.group({
          //...other controls...
          addOns: fb.array([])
      })
  }
  ngOnInit(){
      this.addonsService.getAll()
      .subscribe(result =&gt;  {
        this.addOns = result;
        for(let addOn in this.addOns) {
          this.form.get('addOns').push(new FormControl(false));
        }
      });
  }
  </code></pre>
  <p>I need to then set the values in the array based on another set of values. I have tried</p>
  <pre><code>var formArray = this.form.get('addOns') as FormArray;
  </code></pre>
  <p>Then looping through, but this doesn't work</p>
  <pre><code>formArray.controls.forEach(c =&gt; {
      c.setValue(true)
  })
  </code></pre>
  <p>I also tried calling by index, but this returns undefined</p>
  <pre><code>formArray.controls[0].setValue(true);
  </code></pre>
  <p>If I console.log() formArray I get the expected number of form controls.</p>
  <p>How can I set the values of the formArray after dynamically building it?</p>