title: Unable to simultaneously satisfy constraints when animating constraint
body: <p>This is my code:</p>
  
  <pre><code>    class AvailableTrainScene: UIView {
            let seeMoreButton: UIButton = {
          let v = UIButton()
          v.translatesAutoresizingMaskIntoConstraints = false
          v.backgroundColor = .blue
          v.layer.cornerRadius = 20
          v.setTitle("Voir Plus", for: .normal)
          return v
      }()
  
      var seeMoreBottom: NSLayoutConstraint?
  
      override init(frame: CGRect) {
          super.init(frame: frame)
          addSubview(seeMoreButton)
      }
  
      required init?(coder aDecoder: NSCoder) {
          super.init(coder: aDecoder)
      }
  
      override func layoutSubviews() {
          NSLayoutConstraint.activate([
              seeMoreButton.heightAnchor.constraint(equalToConstant: 40),
              seeMoreButton.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 0.8),
              seeMoreButton.centerXAnchor.constraint(equalTo: centerXAnchor)
              ])
              seeMoreBottom = seeMoreButton.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -8)
          seeMoreBottom?.isActive = false
      }
  
      func hideSeeMore(_ hide: Bool) {
          if hide {
              seeMoreBottom?.constant = 40
          }else{
              seeMoreBottom?.constant = -8
          }
          UIView.animate(withDuration: 0.4, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: 4, options: .curveEaseOut, animations: {
              self.layoutIfNeeded()
          }, completion: nil)
      }
  }
  </code></pre>
  
  <p>i get this error when animating using the function hideSeeMore:</p>
  
  <pre><code>LayoutConstraints] Unable to simultaneously satisfy constraints.
      Probably at least one of the constraints in the following list is one you don't want. 
      Try this: 
          (1) look at each constraint and try to figure out which you don't expect; 
          (2) find the code that added the unwanted constraint or constraints and fix it. 
  (
      "&lt;NSLayoutConstraint:0x28060dc70 UIButton:0x105534920'Voir Plus'.bottom == DzTrain_2_0.AvailableTrainScene:0x1055300d0.bottom - 8   (active)&gt;",
      "&lt;NSLayoutConstraint:0x2806894a0 UIButton:0x105534920'Voir Plus'.bottom == DzTrain_2_0.AvailableTrainScene:0x1055300d0.bottom + 40   (active)&gt;"
  )
  
  Will attempt to recover by breaking constraint 
  &lt;NSLayoutConstraint:0x2806894a0 UIButton:0x105534920'Voir Plus'.bottom == DzTrain_2_0.AvailableTrainScene:0x1055300d0.bottom + 40   (active)&gt;
  
  Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
  The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in &lt;UIKitCore/UIView.h&gt; may also be helpful.
  </code></pre>
  
  <p>i tried to add tow constraints one to hide and another to show (priority is deferent) then activate/deactivate them but nothing happend?
  Someone have this before?</p>