Creating Auto Layout constraints to topLayoutGuide and bottomLayoutGuide in code

For a UIButton that you want to place 20 points below the UIViewController.topLayoutGuide you create the NSLayoutConstraint like so:

[NSLayoutConstraint constraintWithItem:self.button
                             attribute:NSLayoutAttributeTop
                             relatedBy:NSLayoutRelationEqual
                                toItem:self.topLayoutGuide
                             attribute:NSLayoutAttributeBottom
                            multiplier:1.0
                              constant:20.0];

With iOS 9 you can also create the NSLayoutConstraint this way:

[self.button.topAnchor constraintEqualToAnchor:self.topLayoutGuide.bottomAnchor
                                      constant:20.0];