title: Add Textview under UIAlertController in Objective-C
body: <p>How can I add a text view under a <code>UIAlertController</code>? I have tried the approach below but the textview is not showing properly.</p>
  
  <pre><code>UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Comments" message:@"Enter your submit comments" preferredStyle:UIAlertControllerStyleAlert];
  alertController.view.autoresizesSubviews = YES;
  
  UITextView * alertTextView = [[UITextView alloc] initWithFrame:CGRectZero];
  alertTextView.translatesAutoresizingMaskIntoConstraints = NO;
  alertTextView.backgroundColor = [UIColor greenColor];
  
  NSLayoutConstraint *leadConstraint = [NSLayoutConstraint constraintWithItem:alertController.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:alertTextView attribute:NSLayoutAttributeLeading multiplier:1.0 constant:-8.0];
  NSLayoutConstraint *trailConstraint = [NSLayoutConstraint constraintWithItem:alertController.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:alertTextView attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:8.0];
  
  NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:alertController.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:alertTextView attribute:NSLayoutAttributeTop multiplier:1.0 constant:-64.0];
  NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:alertController.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:alertTextView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:64.0];
  [alertController.view addSubview:alertTextView];
  [NSLayoutConstraint activateConstraints:@[leadConstraint, trailConstraint, topConstraint, bottomConstraint]];
  
  UIAlertAction *okButtonAction = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction *  action) {
      [alertTextView resignFirstResponder];
  
  }];
  UIAlertAction *cancelButtonAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {
  
  }];
  [alertController addAction:okButtonAction];
  [alertController addAction:cancelButtonAction];
  
  [self presentViewController:alertController animated:YES completion:nil];
  </code></pre>