didset

问题 I have a @State Bool variable with didSet on it. I want to do something when the variable change therefore I have tried to use didSet. The problem is when I use the .toggle() function to toggle the state of the bool, didSet is not called. Take this code for example: import SwiftUI struct SwiftUIView: View { @State var testBool = false { didSet { print("set") } } var body: some View { VStack { Button(action: { self.testBool.toggle() }) { Text("Toggle with .toggle()") } Button(action: { if self

问题 I have a SwiftUI (Beta 5) view with an attached ViewModel. I want to navigate to it via a navigationLink and pass in a simple parameter (called FSAC in this case) I navigate using NavigationLink("Next", destination: MyTestView(FSAC: "testFsac")) The view has an FSAC Property with willSet and didSet property observer struct MyTestView: View { @ObservedObject var vm = MyTestViewModel() var FSAC: String { willSet { print("will set fsac") } didSet { print("did set fsac") vm.FSAC = FSAC } } var

问题 I have a SwiftUI (Beta 5) view with an attached ViewModel. I want to navigate to it via a navigationLink and pass in a simple parameter (called FSAC in this case) I navigate using NavigationLink("Next", destination: MyTestView(FSAC: "testFsac")) The view has an FSAC Property with willSet and didSet property observer struct MyTestView: View { @ObservedObject var vm = MyTestViewModel() var FSAC: String { willSet { print("will set fsac") } didSet { print("did set fsac") vm.FSAC = FSAC } } var

问题 I have a general problem using toggles with SwiftUI. Whenever I use them I get this console error: invalid mode 'kCFRunLoopCommonModes' provided to CFRunLoopRunSpecific - break on _CFRunLoopError_RunCalledWithInvalidMode to debug. This message will only appear once per execution. In addition to this didSet does not print anything when I hit the toggle in the simulator. Does anyone have an idea, or is it a SwiftUI bug? Other related questions on StackOverflow which are some month old didn't

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

问题 What is the difference between willSet - didSet , and get - set , when working with this inside a property? From my point of view, both of them can set a value for a property. When, and why, should I use willSet - didSet , and when get - set ? I know that for willSet and didSet , the structure looks like this: var variable1 : Int = 0 { didSet { println (variable1) } willSet(newValue) { .. } } var variable2: Int { get { return variable2 } set (newValue){ } } 回答1: When and why should I use

问题 below is my code. I want the value for Latitude and Longitude in my Poststring. But When he do the poststring my values are still nil because swift didn't update the location yet. So how can I wait for latitude and longitude before poststring gets the Values? I heard something of didset but I don't know how to use it and where I have to use it. import Foundation import CoreLocation protocol FeedmodelProtocol: class { func itemsDownloaded(items: NSArray) } class Feedmodel: NSObject,

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 =

问题 I have a class as property with a property observer. If I change something in that class, is there a way to trigger didSet as shown in the example: class Foo { var items = [1,2,3,4,5] var number: Int = 0 { didSet { items += [number] } } } var test: Foo = Foo() { didSet { println("I want this to be printed after changing number in test") } } test.number = 1 // Nothing happens 回答1: Nothing happens because the observer is on test , which is a Foo instance. But you changed test.number , not test

问题 I'm wondering, when/how does the didSet on an outlet actually trigger? For example : @IBOutlet weak var modifyButton: UIButton! { didSet { modifyButton.layer.cornerRadius = 9 } } 回答1: Outlet properties initialized as nil when class just initialized. They will have values later, when objects will be initialized from nib. First step, when you can be sure that all properly configured outlet properties have nonnil values is viewDidLoad . So, didSet observer on this properties will be called just