AutoLayout example of centering a view horizontally. Refer to: http://stackoverflow.com/questions/12873372/centering-a-view-in-its-superview-using-visual-format-language

AutoLayout CenterX

[NSLayoutConstraint constraintWithItem:view
                             attribute:NSLayoutAttributeCenterX
                             relatedBy:NSLayoutRelationEqual
                                toItem:view.superview
                             attribute:NSLayoutAttributeCenterX
                            multiplier:1.f constant:0.f];