title: Hide autolayout UIView : How to get existing NSLayoutConstraint to update this one
body: <p>I know how to modify a existing constraint. But I would to know if someone has found a solution to get a constraint without save this one as a property.</p>
  
  <p>Current solution to set Constraint height:</p>
  
  <p><strong>1) save NSLayoutConstraint in a variable:</strong></p>
  
  <pre><code>NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:myView
                                                                      attribute:NSLayoutAttributeHeight
                                                                      relatedBy:NSLayoutRelationEqual
                                                                         toItem:nil
                                                                      attribute:NSLayoutAttributeNotAnAttribute
                                                                     multiplier:1.0f
                                                                       constant:20];
  [self.view addConstraint:heightConstraint];
  </code></pre>
  
  <p><strong>2) Set the constant of the Constraint saved to "0.0" ( to hide this view)</strong></p>
  
  <pre><code>[heightConstraint setConstant:200];
  </code></pre>
  
  <hr>
  
  <p><strong>I'm looking for a solution like this:</strong></p>
  
  <pre><code> [myView setConstraint:@"0." forAttribute:NSLayoutAttributeHeight]
  </code></pre>