property-observer | 易学教程

In Swift, does resetting the property inside didSet trigger another didSet?

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问题 I'm testing this and it appears that if you change the value within didSet , you do not get another call to didSet . var x: Int = 0 { didSet { if x == 9 { x = 10 } } } Can I rely on this? Is it documented somewhere? I don't see it in the Swift Programming Language document. 回答1: I also thought, that this is not possible (maybe it wasn't in Swift 2), but I tested it and found an example where Apple uses this. (At "Querying and Setting Type Properties") struct AudioChannel { static let

How can I observe a specific element with Swift collection types using property observers?

阅读更多关于 How can I observe a specific element with Swift collection types using property observers?

问题 Inspired when answering the question of How do I know if a value of an element inside an array was changed?, The answer was using a Property Observer for checking if an array has been modified. However, How can I determine what is/are the updated element(s) in a collection type in a property observer? For example: class MyClass { var strings: [String] = ["hello", "world", "!"] { didSet(modifiedStrings) { print("strings array has been modified!!:") print(modifiedStrings) } } } let myClass =

How can I observe a specific element with Swift collection types using property observers?

阅读更多关于 How can I observe a specific element with Swift collection types using property observers?

Inner didSet protection bizarrely extends to the whole class?

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问题 It's well-known that, of course, didSet will not run on the same object again from inside a didSet. (example.) However. It seems that: the restriction applies not only to that object, but to maybe any object of the same class . Here are copy-paste test cases for Playground. class C { var Test: Bool = false { didSet { print("test.") for c in r { c.Test = true } } } var r:[C] = [] } var a:C = C() var b:C = C() var c:C = C() a.r = [b, c] a.Test = false Does not work! class C { var Test2: Bool =

Why property observer doesn't work with classes? [duplicate]

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问题 This question already has an answer here : Is there a way to get didSet to work when changing a property in a class? (1 answer) Closed last year . Using Playground. I have the following structure: struct Foo { var name: String var age: Int init(name: String, age: Int) { self.name = name self.age = age } } I declared an instance from it as property observer with default values as "James" for the name and 33 for the age : var myFoo = Foo(name: "James", age: 33) { willSet { print("my foo will be

What makes a property a computed property in Swift

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问题 Let's started with the code snippet: St Foo { var proA: Int = 0 { // needs initialization willSet { print("about to set proA to \(newValue) from \(proA)") } didSet { print("already set proA to \(proA) from \(oldValue)") } } var ProB: Int { // do not needs initialization return 1 } } let foo = Foo() foo.proA = 23 print(foo.ProB) Here are some of my personal understandings about the the stored and computed property: a: Property with only the observer (willSet and didSet) is not a computed

In Swift, does resetting the property inside didSet trigger another didSet?

阅读更多关于 In Swift, does resetting the property inside didSet trigger another didSet?

I'm testing this and it appears that if you change the value within didSet , you do not get another call to didSet . var x: Int = 0 { didSet { if x == 9 { x = 10 } } } Can I rely on this? Is it documented somewhere? I don't see it in the Swift Programming Language document. I also thought, that this is not possible (maybe it wasn't in Swift 2), but I tested it and found an example where Apple uses this. (At "Querying and Setting Type Properties") struct AudioChannel { static let thresholdLevel = 10 static var maxInputLevelForAllChannels = 0 var currentLevel: Int = 0 { didSet { if currentLevel

How can I observe a specific element with Swift collection types using property observers?

阅读更多关于 How can I observe a specific element with Swift collection types using property observers?

Inspired when answering the question of How do I know if a value of an element inside an array was changed? , The answer was using a Property Observer for checking if an array has been modified. However, How can I determine what is/are the updated element(s) in a collection type in a property observer? For example: class MyClass { var strings: [String] = ["hello", "world", "!"] { didSet(modifiedStrings) { print("strings array has been modified!!:") print(modifiedStrings) } } } let myClass = MyClass() myClass.strings.append("a string") myClass.strings[0] = "Hello" myClass.strings.removeLast()