title: Unable to change UIInputView height
body: <p>I have a simple UIInputViewController subclass with only two overridden methods. I use this input view controller as <code>inputAccessoryViewController</code> on my UIViewController subclass which becomes first responder. I try to specify height of inputView by adding constraint as Apple documentation recommends.
  Problem is that my constraint doesn't work and I get autolayout exception when my constraint is being added</p>
  
  <pre><code>Unable to simultaneously satisfy constraints.
  Probably at least one of the constraints in the following list is one you don't want.
  ...
  (
      "&lt;NSLayoutConstraint:0x178aa1d0 V:[UIInputView:0x178a4ae0(0)]&gt;",
      "&lt;NSLayoutConstraint:0x178b9520 V:[UIInputView:0x178a4ae0(500)]&gt;"
  )
  Will attempt to recover by breaking constraint 
  &lt;NSLayoutConstraint:0x178b9520 V:[UIInputView:0x178a4ae0(500)]&gt;
  </code></pre>
  
  <p>Which I think means that system already added a zero height constraint to the input view (because it is created with zero height). Now they conflict and autolayout breaks my constraint to fix the issue. </p>
  
  <p>When I try to use it as <code>inputViewController</code> of my view controller (just for test purposes), I get same exception but instead of zero height it is 216 px. It also breaks my constraint and the height remains default.</p>
  
  <pre><code>- (void)viewDidLoad {
      [super viewDidLoad];
      // Do any additional setup after loading the view from its nib.
  
      self.inputView.translatesAutoresizingMaskIntoConstraints = NO;
      self.inputView.backgroundColor = [UIColor redColor];
  }
  
  - (void)updateViewConstraints {
  
      CGFloat _expandedHeight = 500;
      NSLayoutConstraint *_heightConstraint = 
      [NSLayoutConstraint constraintWithItem:self.view
                                   attribute:NSLayoutAttributeHeight
                                   relatedBy:NSLayoutRelationEqual
                                      toItem:nil
                                   attribute:NSLayoutAttributeNotAnAttribute
                                   multiplier:0.0
                                     constant: _expandedHeight];
      [self.inputView addConstraint: _heightConstraint];
  
      [super updateViewConstraints];
  }
  
  -(void)viewDidAppear:(BOOL)animated
  {
      [super viewDidAppear:animated];
      [self.view setNeedsUpdateConstraints];
  }
  </code></pre>
  
  <p>As a result, I am not able to change input accessory view height. Has anyone succeed in it?  Obviously, Apple documentation provides no help...</p>