property-observer

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

由 大憨熊 提交于 2020-01-10 12:37:32
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?

由 别来无恙 提交于 2019-12-29 08:18:26
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?

由 送分小仙女□ 提交于 2019-12-29 08:18:21
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 =

Inner didSet protection bizarrely extends to the whole class?

由 ∥☆過路亽．° 提交于 2019-12-23 13:26:15
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]

由 ☆樱花仙子☆ 提交于 2019-12-11 14:56:16
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

由 人盡茶涼 提交于 2019-12-10 10:23:38
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?

由 心已入冬 提交于 2019-11-30 17:32:05
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?

由 戏子无情 提交于 2019-11-29 12:45:35
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()
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