Introduction to Swift lazy loading and read-only properties

Lazy Loading

Lazy loading is ubiquitous in IOS development

• Lazy loading format is as follows:

var person: Person = {    print("懒加载")    return Person()}()

• Lazy loading is essentially a closed package
• The above code can be rewritten in the following format

let personFunc = { () -> Person in    print("懒加载") return Person()}lazy var demoPerson: Person = self.personFunc()

• A simple notation for lazy loading

var demoPerson: Person = Person()

Read-only property getter & Setter

• getter & setterrarely used in Swift, the following code is for information only

var _name: String?var name: String? {    get { return _name } set { _name = newValue }}

Storage-Type Properties & computed properties

• Storage-type properties-need to open up space to store data
• Computed properties-Execution functions return other memory addresses

var title: String {    get {        return "Mr " + (name ?? "") }}

• A property that implements only getter methods is called a computed property, equivalent to the ReadOnly attribute in OC
• Computed properties themselves do not occupy memory space
• You cannot set a value for a computed property
• Computed properties can use the following code shorthand

var title: String {    return "Mr " + (name ?? "")}

Comparison of computed properties with lazy loading

• Computed properties
  • Do not allocate independent storage space to save calculation results
  • Executed each time it is called
  • More like a function, but cannot receive parameters, and must have a return value

var title2: String {    return "Mr" + (name ?? "")}

• Lazy Load Properties
  • When the first call is performed, the closure is executed and the value returned by the space storage closure is allocated
  • Separate storage space is allocated
  • Unlike OC, the Lazy property is not called again even if it is set to nil

var title: String = {    return "Mr " + (self.name ?? "")}()

Introduction to Swift lazy loading and read-only properties