1. Ioannis Pavlidis Dinesh Majeti Ashik Khatri
Lecture 3
Ioannis Pavlidis
Dinesh Majeti
Ashik Khatri

2. Overview
Protocols
Delegates
UIStackView

3. Protocols Specifies a list of methods like a “contract” or “interface”
A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality
Any type that satisfies the requirements of a protocol is said to conform to that protocol
Protocols can be made optional and optional keywords

4. Protocols Defined similar to classes, structures, and enumerations
Property requirements are declared as variable properties
protocol SomeProtocol {
func doSomething()
var mustBeSettable: Int { get set }
var doesNotNeedToBeSettable: Int { get } }
@objc protocol SomeProtocol {
optional func doSomething()

5. Implementing a protocol
protocol RandomNumberGenerator { func random() -> Double }
class SomeClass: RandomNumberGenerator {
var lastRandom = 42.0
let m =
let a =
let c =
func random() -> Double {
lastRandom = ((lastRandom * a + c) % m)
return lastRandom / m }

6. Delegation
Enables a class or structure to hand off (or delegate) some of its responsibilities to an instance of another type.
Can be used to respond to a particular action
Retrieve data from an external source without needing to know the underlying type of that source.

7. Example Start with a simple protocol protocol UITextFieldDelegate {
func textFieldShouldReturn(_ textField: UITextField) -> Bool }

8. Protocol as a Type class UITextField {
var delegate: UITextFieldDelegate?
var text: String?
//… some other stuff }

9. Delegating responsibility
class Controller: UITextFieldDelegate {
var textField = UITextField()
textField.delegate = self
func textFieldShouldReturn() -> Bool {
// do something when text field returns. }

10. Delegates everywhere UITableView
Example: When a table row is tapped, when a table view cell is displayed, etc.
UITextField
Example: Notifying when the user stops typing, hits the return key, etc
Classes like UITableView, UITextField, do not provide implementation details for certain events. These are delegated off to any class that conforms to the protocols

11. UIStackView
Provides a streamlined interface for laying out a collection of views in either a column or a row
Creating user interfaces that can dynamically adapt to the device’s
orientation,
screen size, and
any changes in the available space
Uses AutoLayout to position and size its arranged views
Stack views can be nested

12. UIStackView
Manages layout of all the views in its arrangedSubviews property
Arranged along the stack view axis, based on their order in the arrangedSubviews array
The exact layout varies depending on the stack view’s properties like
axis,
distribution,
alignment,
spacing

13. References Protocols and Delegates UIStackView Tutorial
More on UIStackView