How to get value of FormControl in angular2

I have the following Form with a FormArray containing FormGroups

 <form [formGroup]="screenForm" novalidate>

  <div formArrayName="iPhoneScreenshots" class="row">
    <div *ngIf="screenForm.controls.iPhoneScreenshots?.length > 0">
      {{screenForm.controls.iPhoneScreenshots?.length }}
      <div *ngFor="let url of screenForm.controls.iPhoneScreenshots.controls; let i=index">
        <div [formGroupName]="i">
          <input class="form-control" formControlName="url">
          <img src="{{app.screenshotUrls[i]}}" class="rounded img-fluid app-screen" style="height:200px"/>
        </div>
      </div>
    </div>
  </div>
</form>

      

        
        
        
      

    

the url values ​​come from an array that is filled through the API in the callback I set the values:

private setScreenShots(app: ItunesApp): void {
if (app.hasOwnProperty('screenshotUrls')) {
  const screenShots = app.screenshotUrls.map(url => {
      return this.fb.group({
        url: [url, Validators.required]
      });
    }
  );
  const screenShotsArray = this.fb.array(screenShots);
  this.screenForm.setControl('iPhoneScreenshots', screenShotsArray);
 }
}

      

        
        
        
      

    

initial array is empty

 private createForm() {
   this.appSiteForm = this.fb.group({
  title: ['', Validators.required]
});

this.screenForm = this.fb.group({
  iPhoneScreenshots: this.fb.array([]),
});

      

        
        
        
      

    

}

this line of code looks very strange to me

img src="{{app.screenshotUrls[i]}}" 

      

        
        
        
      

    

I am doing this because url.value () or url.get ('value') throws errors.

So how can I access the value of a form control?