I have already seen
Is it possible to allow didSet to be called during initialization in Swift?
for me it is not working..
I am working in project where I have created class below
protocol FileManagerHelper {
var fileName:String {get}
var fileCategory:FileCategory {get set}
var isFileExitsAtPath:Bool {get}
var filePath:String {get}
var fileType:FileTypes {get set}
}
class FileManager:FileManagerHelper {
// Other property
//STORED PROPERY INIT WHEN OBJECT WILL CREATED WITH FileCategory OBJECT
var fileCategory:FileCategory {
didSet {
switch fileCategory {
case .XYZ:
print("Test")
... other cases
}
}
required init(fileCategory:FileCategory,fileType:FileTypes = .Image) {
self.fileCategory = fileCategory
self.path = self.folderPath + self.fileName
}
}
did set method is not calling of fileCategory
NOTE: I don't want to give default value , I want to pass it runtime from init method
Tries
1) defer
use of self in method called $defer before all stored property are initialised
2) Create custom method that will assign that value and call it from init
private func setCategory(with category:FileCategory) {
self.fileCategory = category
}
Use of method call setCategory before stored property ...
I know that all stored property should be initialised before instance created. Till that instance will not been created so i won't call methods (using self) may be that why above solution not working
Please help me if any one have idea
For me, using the defer is better readable.
import Foundation
class A {
var b: String {
didSet {
print("didSet called with value: \(b)")
}
}
init(x: String) {
self.b = x
defer { self.b = x }
}
}
let a = A(x: "It's Working!") // didSet called with value: It's Working!
print(a.b) // It's Working
One way to solve this is to extract the didSet logic into a separate method and call this method from both didSet and init:
class FileManager: FileManagerHelper {
var fileCategory:FileCategory {
didSet {
didSetFileCategory()
}
}
required init(fileCategory:FileCategory,fileType:FileTypes = .Image) {
self.fileCategory = fileCategory
self.path = self.folderPath + self.fileName
didSetFileCategory()
}
private func didSetFileCategory() {
switch fileCategory {
case .XYZ:
print("Test")
//... other cases
}
}
}
Related
I am trying to write a property wrapper to bind two variables together. The problem I am having is that when I call the projectedValue property my closure returns nil. I want to be able to assign a value to the closure once the value of the observed item is changed.
This is my property wrapper class.
#propertyWrapper
class State<Instance> {
typealias projectedClosure = (Instance) ->Void
init(wrappedValue: Instance) {
self.instance = wrappedValue
}
var projectedValue : Binding<Instance> {
Binding<Instance>(value: instance)
}
private var instance : Instance {
didSet{
projectedValue.value = instance
}
}
var wrappedValue: Instance {
get{
return instance
}
set{
instance = newValue
}
}
}
The propertyWrapper projects this class
class Binding<Element> {
var handler : ((Element)->Void)?
var value :Element {
didSet{
guard let handlerClosure = handler else {
print("Handler is null")
return
}
handlerClosure(value)
}
}
init(value:Element) {
self.value = value
}
}
Finally, I am implementing this in a playground before porting it over into my actual project. This is how I am executing the methods.
class TestPropertyWrapperObserver {
#State var name : String
init(name:String) {
self.name = name
}
}
var test = TestPropertyWrapperObserver(name: "Thomas")
var ryan = "ryan"
test.$name.handler = { item in
ryan = item
print(item)
}
test.name = "bradly"
test.name = "fake"
print(ryan)
My print log is:
Handler is null
Handler is null
ryan
Your mistake is that you made projectedValue a computed property, so every time you do this:
projectedValue.value = instance
a new Binding instance is created.
Instead, you should make projectedValue a stored property, and initialise it in init, once:
init(wrappedValue: Instance) {
self.instance = wrappedValue
projectedValue = Binding<Instance>(value: instance)
}
let projectedValue : Binding<Instance>
I was wondering if there is a way to do this in a better way with generics. I have this singleton which needs a setter and another getter for every object. Plus, I have to check that the property is not nil in every getter, which is a lot of repeated code. ex:
class DataManager : NSObject {
private override init(){}
private var postData : [PostModel]?
private var userData : [UserModel]?
private var commentsData : [CommentsModel]?
private var photosData : [PhotosModel]?
private var albumsData : [AlbumsModel]?
private var todosData : [TodosModel]?
static let shared = DataManager()
//MARK : Setters
func setUserData(data : [UserModel]) {
self.userData = data
}
func setPostData(data : [PostModel]) {
self.postData = data
}
func setCommentsData(data : [CommentsModel]) {
self.commentsData = data
}
func setAlbumsData(data : [AlbumsModel]) {
self.albumsData = data
}
func setPhotosData(data : [PhotosModel]) {
self.photosData = data
}
func setTodosData(data : [TodosModel]) {
self.todosData = data
}
//MARK : Getters
func getUserData() -> [UserModel]? {
if self.userData != nil {
return self.userData!
}
return nil
}
func getPostData() -> [PostModel]? {
if self.postData != nil {
return self.postData!
}
return nil
}
func getCommentsData() -> [CommentsModel]? {
if self.commentsData != nil {
return self.commentsData!
}
return nil
}
func getAlbumsData() -> [AlbumsModel]? {
if self.albumsData != nil {
return self.albumsData!
}
return nil
}
func getPhotosData() -> [PhotosModel]? {
if self.photosData != nil {
return self.photosData!
}
return nil
}
func getTodosData() -> [TodosModel]? {
if self.todosData != nil {
return self.todosData!
}
return nil
}
}
I was wondering if all this logic could be done in one single method, maybe using generics?
If you want to force all object to set as a none optional and also get as a none optional, you don't need to define them as optional at the first place:
So instead of:
private var postData : [PostModel]?
you should have:
private var postData = [PostModel]()
This will gives you an empty none optional array and it can not be set or get as an optional.
If you want them to be nil before someone get them (for memory management or etc.), You can make them lazy:
private lazy var postData = [PostModel]()
So now postData will be nil until someone tries to read the value of it.
If you need to do some extra job when someone tries to set one of these, you can observe for changes before set and after set of the value:
private var postData = [PostModel]() {
willSet { /* right before the value is going to set */ }
didSet { /* right after the value is set */ }
}
Note that lazy properties can not have observers
So seems like you don't have any of the functions at all. And you can refactor your code to something like this:
class DataManager : NSObject {
private override init(){}
lazy var postData = [PostModel]()
lazy var userData = [UserModel]()
lazy var commentsData = [CommentsModel]()
lazy var photosData = [PhotosModel]()
lazy var albumsData = [AlbumsModel]()
lazy var todosData = [TodosModel]()
}
I'm trying to pass data between viewControllers, but something seems wrong.
The first viewController I want to set the "Bool" to the protocol function to be able to recover in the other screen. What am I doing wrong, I always used protocols but at this time I got in trouble.
That's how I'm doing that:
//
// ComboBoxNode.swift
//
import Foundation
import SWXMLHash
protocol ComboBoxNodeDelegate {
func getCustomOption(data:Bool)
}
class ComboBoxNode: FormControlNode, IFormControlDataSource {
var listType: String?
var dataSource: String?
var dataSourceValue: String?
var dataSourceText: String?
var hasCustomOption:Bool?
var customOptionText: String?
var ctrlDataSourceType: String?
var parameters = [ParameterNode]()
var staticList: FormControlStaticListNode?
var delegate:ComboBoxNodeDelegate?
override init(indexer: XMLIndexer) {
super.init(indexer: indexer)
guard let element = indexer.element else {
preconditionFailure("Error")
}
let isCustomOption = element.bool(by: .hasCustomOption) ?? hasCustomOption
if isCustomOption == true {
self.delegate?.getCustomOption(data: hasCustomOption!)
}
self.readFormControlDataSource(indexer: indexer)
}
override func accept<T, E: IViewVisitor>(visitor: E) -> T where E.T == T {
return visitor.visit(node: self)
}
}
That's how I'm trying to recover on next screen:
// FormPickerViewDelegate.swift
import Foundation
import ViewLib
import RxSwift
class FormPickerViewDelegate: NSObject {
var items = Variable([(value: AnyHashable, text: String)]()) {
didSet {
PickerNodeDelegate = self
self.setDefaultValues()
}
}
private var controlViewModel: FormControlViewModel
private var customText:Bool?
private var PickerNodeDelegate:ComboBoxNodeDelegate?
init(controlViewModel: FormControlViewModel) {
self.controlViewModel = controlViewModel
}
func getItemByValue(_ value: Any) -> (AnyHashable, String)? {
if value is AnyHashable {
let found = items.value.filter {$0.value == value as! AnyHashable}
if found.count >= 1 {
return found[0]
}
}
return nil
}
}
extension FormPickerViewDelegate:ComboBoxNodeDelegate {
func getCustomOption(data: Bool) {
customText = data
}
}
Instead of setting PickerNodeDelegate = self in didSet {} closure
var items = Variable([(value: AnyHashable, text: String)]()) {
didSet {
PickerNodeDelegate = self
self.setDefaultValues()
}
}
Assign it in your init() function instead
init(controlViewModel: FormControlViewModel) {
self.controlViewModel = controlViewModel
PickerNodeDelegate = self
}
Note, your should declare your delegate to be weak also, since it's a delegate, your protocol should conform to be a class type in order to be weakified.
protocol ComboBoxNodeDelegate: class
...
weak var delegate: ComboBoxNodeDelegate?
Here is an example, hope it helps!
protocol ComboBoxNodeDelegate {
func getCustomOption(data:Bool) -> String
}
class ViewOne:ComboBoxNodeDelegate {
var foo:Bool = false
var bar:String = "it works!"
/** Return: String */
func getCustomOption(data:Bool) -> String { //conform here to protocol
// do whatever you wanna do here ...example
self.foo = data // you can set
return bar // even return what you want
}
//initialize
func initalizeViewTwo() {
let v2 = ViewTwo()
v2.delegate = self //since `self` conforms to the ComboBoxNodeDelegate protcol you are allowed to set
}
}
class ViewTwo {
var delegate:ComboBoxNodeDelegate?
func getCustomOption_forV1() {
let view2_foo = delegate.getCustomOption(data:true)
print(view2_foo) // should print "it works!"
}
}
All parameters passed around in Swift are constants -- so you cannot change them.
If you want to change them in a function, you must declare your protocol to pass by reference with inout:
protocol ComboBoxNodeDelegate {
func getCustomOption(data: inout Bool)
}
Note: you cannot pass a constant (let) to this function. It must be a variable -- which I see you are doing!
So, i am creating a Singleton class as below, and i need few instance variables in this class, such that any team member can access the instance variable and get the values. To do that, i will need to initialize these instance variables to a certain value at the beginning itself.
But i get a compilation error, saying "missing argument for parameter 'doesValueExists' in call".
What exactly i m doing wrong here ?
class ABC_Util {
private var doesValueExists: Bool
private var arrValues: NSMutableArray?
class var sharedInstance: ABC_Util {
struct ABC_UtilSingleton {
static let instance = ABC_Util()
}
return ABC_UtilSingleton.instance
}
init(doesValueExists: Bool, arrValues: NSMutableArray?) {
self.doesValueExists = self.checkValueExists()
self.arrValues = self.getArrayOfValues()
}
//method
internal func checkValueExists() -> Bool {
}
//method
internal func getArrayOfValues() -> NSMutableArray? {
}
}
Your initializer for ABC_Util is declared as:
init(doesValueExists:Bool, arrValues:NSMutableArray?) {
Therefore you cannot say
static let instance = ABC_Util()
The expression ABC_Util() would correspond to an initializer with no parameters, and you do not have such an initializer. You must say:
static let instance = ABC_Util(doesValueExists:someBool, arrValues:someArray)
(with appropriate values, of course).
You have to use your initializer in order to initialize your variables.
class ABC_Util {
private var doesValueExists:Bool
private var arrValues:NSMutableArray?
class var sharedInstance: ABC_Util
{
struct ABC_UtilSingleton
{
static let instance = ABC_Util(doesValueExists: true, arrValues: nil)
}
return ABC_UtilSingleton.instance
}
init(doesValueExists:Bool, arrValues:NSMutableArray?) {
self.doesValueExists = doesValueExists
self.arrValues = arrValues
}
//method
internal func checkValueExists()-> Bool
{
return true
}
//method
internal func getArrayOfValues()-> NSMutableArray?
{
return nil
}
}
And I recommend you to change your singleton declaration to the suggested syntax
static let sharedInstance: ABC_Util = ABC_Util(doesValueExists: true, arrValues: nil)
You could use as below.
class ABC_Util {
private var doesValueExists:Bool = false
private var arrValues:NSMutableArray?
class var sharedInstance: ABC_Util {
struct ABC_UtilSingleton {
static let instance = ABC_Util(doesValueExists: false, arrValues: ["a", "b", "c"])
}
return ABC_UtilSingleton.instance
}
init(doesValueExists:Bool, arrValues:NSMutableArray?) {
self.doesValueExists = self.checkValueExists()
self.arrValues = self.getArrayOfValues()
}
//method
internal func checkValueExists()-> Bool{
return self.doesValueExists
}
//method
internal func getArrayOfValues()-> NSMutableArray?{
return arrValues
}
}
i got the solution, when i tried this, worked fine!
class ABC_Util {
var doesValueExists:Bool = false
var arrValues:NSMutableArray? = nil
class var sharedInstance: ABC_Util
{
struct ABC_UtilSingleton
{
static let instance = ABC_Util()
}
return ABC_UtilSingleton.instance
}
init() {
self.doesValueExists = self.checkValueExists()
self.arrValues = self.getArrayOfValues()
}
//method
internal func checkValueExists()-> Bool
{
//return true/false
}
//method
internal func getArrayOfValues()-> NSMutableArray?
{
//return array/nil
}
}
Question
Apple's docs specify that:
willSet and didSet observers are not called when a property is first initialized. They are only called when the property’s value is set outside of an initialization context.
Is it possible to force these to be called during initialization?
Why?
Let's say I have this class
class SomeClass {
var someProperty: AnyObject {
didSet {
doStuff()
}
}
init(someProperty: AnyObject) {
self.someProperty = someProperty
doStuff()
}
func doStuff() {
// do stuff now that someProperty is set
}
}
I created the method doStuff, to make the processing calls more concise, but I'd rather just process the property within the didSet function. Is there a way to force this to call during initialization?
Update
I decided to just remove the convenience intializer for my class and force you to set the property after initialization. This allows me to know didSet will always be called. I haven't decided if this is better overall, but it suits my situation well.
If you use defer inside of an initializer, for updating any optional properties or further updating non-optional properties that you've already initialized and after you've called any super.init() methods, then your willSet, didSet, etc. will be called. I find this to be more convenient than implementing separate methods that you have to keep track of calling in the right places.
For example:
public class MyNewType: NSObject {
public var myRequiredField:Int
public var myOptionalField:Float? {
willSet {
if let newValue = newValue {
print("I'm going to change to \(newValue)")
}
}
didSet {
if let myOptionalField = self.myOptionalField {
print("Now I'm \(myOptionalField)")
}
}
}
override public init() {
self.myRequiredField = 1
super.init()
// Non-defered
self.myOptionalField = 6.28
// Defered
defer {
self.myOptionalField = 3.14
}
}
}
Will yield:
I'm going to change to 3.14
Now I'm 3.14
Create an own set-Method and use it within your init-Method:
class SomeClass {
var someProperty: AnyObject! {
didSet {
//do some Stuff
}
}
init(someProperty: AnyObject) {
setSomeProperty(someProperty)
}
func setSomeProperty(newValue:AnyObject) {
self.someProperty = newValue
}
}
By declaring someProperty as type: AnyObject! (an implicitly
unwrapped optional), you allow self to fully initialize without
someProperty being set. When you call
setSomeProperty(someProperty) you're calling an equivalent of
self.setSomeProperty(someProperty). Normally you wouldn't be able to
do this because self hasn't been fully initialized. Since
someProperty doesn't require initialization and you are calling a
method dependent on self, Swift leaves the initialization context and
didSet will run.
As a variation of Oliver's answer, you could wrap the lines in a closure. Eg:
class Classy {
var foo: Int! { didSet { doStuff() } }
init( foo: Int ) {
// closure invokes didSet
({ self.foo = foo })()
}
}
Edit: Brian Westphal's answer is nicer imho. The nice thing about his is that it hints at the intent.
I had the same problem and this works for me
class SomeClass {
var someProperty: AnyObject {
didSet {
doStuff()
}
}
init(someProperty: AnyObject) {
defer { self.someProperty = someProperty }
}
func doStuff() {
// do stuff now that someProperty is set
}
}
This works if you do this in a subclass
class Base {
var someProperty: AnyObject {
didSet {
doStuff()
}
}
required init() {
someProperty = "hello"
}
func doStuff() {
print(someProperty)
}
}
class SomeClass: Base {
required init() {
super.init()
someProperty = "hello"
}
}
let a = Base()
let b = SomeClass()
In a example, didSet is not triggered. But in b example, didSet is triggered, because it is in the subclass. It has to do something with what initialization context really means, in this case the superclass did care about that
While this isn't a solution, an alternative way of going about it would be using a class constructor:
class SomeClass {
var someProperty: AnyObject {
didSet {
// do stuff
}
}
class func createInstance(someProperty: AnyObject) -> SomeClass {
let instance = SomeClass()
instance.someProperty = someProperty
return instance
}
}
In the particular case where you want to invoke willSet or didSet inside init for a property available in your superclass, you can simply assign your super property directly:
override init(frame: CGRect) {
super.init(frame: frame)
// this will call `willSet` and `didSet`
someProperty = super.someProperty
}
Note that Charlesism solution with a closure would always work too in that case. So my solution is just an alternative.
unfortunately, didSet observers aren't called when a root class is initialized.
If your class isn't a subclass, you have to use getters and setters to achieve the functionality you want:
class SomeClass {
private var _test: Int = 0
var test: Int {
get { _test }
set { _test = newValue }
}
init(test: Int) { self.test = test }
}
alternatively, if your class is a subclass, you can use didSet and do:
override init(test: int) {
super.init()
self.test = test
}
The didSet SHOULD get called after super.init() is called.
One thing I have not tried but MIGHT also work:
init(test: int) {
defer { self.test = test }
}
NOTE: you will need to make your properties nullable, or set a default value for them, or unwrap the class properties.
You can solve it in obj-с way:
class SomeClass {
private var _someProperty: AnyObject!
var someProperty: AnyObject{
get{
return _someProperty
}
set{
_someProperty = newValue
doStuff()
}
}
init(someProperty: AnyObject) {
self.someProperty = someProperty
doStuff()
}
func doStuff() {
// do stuff now that someProperty is set
}
}