AutoLayoutprogrammatically

Auto Layout programmatically :

1. translatesAutoresizingMaskIntoConstraints :
   • For programmatically created view default value is true and views from interface builder is false.
   • If this property set too True, the system automatically creates a set of constraints based on view’s frame and its autoresizing mask.
   • If you add your own constraint on top of this, they inevitably Conflict with the autogenerated constraints. 
   • Error : [LayoutConstraints] Unable to simultaneously satisfy constraints. (Error will get for conflict)
   • This creates an unsatisfiable layout. So When programmatically instantiating views.
   • Be sure to set their translatesAutoresizingMaskIntoConstraints property to NO.
2. Layout Anchors :

Auto Layout constraints : * Constraints are set off rule to make os know where to place UI Components. introduced in iOS6 and iPadOS6. * There are two ways to set constraint UI Builder and programmatically.

• First Step: let view = UIView(frame: .zero) view.translatesAutoresizingMaskIntoConstraints = false
• Second Step: There are two ways to set constraint programmatically i.e Anchors or Visual Format Language (or VFL).
• Eg :
  • Anchors Language. view.heightAnchor.constraint(equalToConstant:100) view.widthAnchor.constraint(equalToConstant:100)
  • VFL let viewDictionary = [“view”: view] let horizontalConstraint = NSLayoutConstraint.constraints(withVisualFormat: “H: [view(100)]”, metrics: nil, views: viewDictionary) let verticalConstraint = NSLayoutConstaint.constaints(withVisualFormat:”V: [view(100)]”,metrics:nil, views:viewDictionary)

Layouts :

locationButton.leadingAnchor.constraint(equalToSystemSpacingAfter: view.leadingAnchor, multiplier: 1)

1. The way to read this line of code is this:
   • “I would like the location button’s leading anchor to be equal to the system spacing (8 pts) after the view’s leading anchor”. 2 . Apple uses a standard margin spacing of 8 pts. Previously we had been setting it manually. But by using this API we don’t have to. We just have to set its multiplier instead.
   • 1 = 8 pts.
   • 2 = 16 pts
   • 3 = 24 pts and so on.
2. This is is functionally equivalent to:
   • locationButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8)
   • if Apple were ever to change the value of their standard spacing, we would adjust automatically.

view.trailingAnchor.constraint(equalToSystemSpacingAfter: searchButton.trailingAnchor, multiplier: 1)

1. We would like the views trailing anchor to be equal to the system spacing after the search button with a multiplier of
2. This is is functionally equivalent to:
   • searchButton.rightAnchor.constraint(equalTo: view.rightAnchor,constant: -8),

Final Result Design: