title: auto layout modify multiplier of constraint programmatically
body: <p>How can I modify the multiplier of a constraint programmatically? I have set the following:</p>
  
  <pre><code>[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0]];
  </code></pre>
  
  <p>and I need to modify it to this:</p>
  
  <pre><code>[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];
  </code></pre>