WhyAutoLayout_rgbview_visualformat.swift

// NSLayoutConstraint

// Given an array of 3 views	
let viewArray = [
   greenView_vf,
   redView_vf,
   blueView_vf
]
// set this value to false to make auto layout work
viewArray.forEach({ $0.translatesAutoresizingMaskIntoConstraints = false })
// add the 3 views to the super view
viewArray.forEach(view_vf.addSubview)
let viewDict = [
  "greenView" : greenView_vf,
  "redView" : redView_vf,
  "blueView" : blueView_vf
]

//1
view_vf.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-[greenView]-15.5-[redView]-|"
                                                      , options: NSLayoutFormatOptions(rawValue: 0)
                                                      , metrics: nil, views: viewDict))
//2
view_vf.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-[blueView]-|"
                                                      , options: NSLayoutFormatOptions(rawValue: 0)
                                                      , metrics: nil, views: viewDict))
//3		
view_vf.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-[greenView]-[blueView]-|"
                                                      , options: NSLayoutFormatOptions(rawValue: 0)
                                                      , metrics: nil, views: viewDict))
//4		
view_vf.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-[redView]-[blueView]-|"
                                                      , options: NSLayoutFormatOptions(rawValue: 0)
                                                      , metrics: nil, views: viewDict))
//5			
greenView_vf.widthAnchor.constraint(equalTo: redView_vf.widthAnchor).isActive = true	
//6
greenView_vf.heightAnchor.constraint(equalTo: blueView_vf.heightAnchor).isActive = true