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>
Related
I want access to SampleMoel's 'head' at ViewModel
How to fix this error?
this is MVVM(not Use combine, RxSwift ... only use Uikit)
SampleViewModel.swift
class SampleViewModel {
var model: SampleModel?
let changeData = Observer(model?.head) //Line error
init() {
self.model = SampleModel()
}
func changeLabel(_ tf: String) {
self.changeData.value = tf
}
}
SampleModel.swift
struct SampleModel {
var head = "initValue"
}
Modify your implementation as follows:
class SampleViewModel {
private let model: SampleModel
let changeData: Observer<String>
init(model: SampleModel) {
self.model = model
changeData = Observer(model.head)
}
func changeLabel(_ tf: String) {
self.changeData.value = tf
}
}
I have a phone number model which looks like this:
import UIKit
import Foundation
struct PhoneValidation : OptionSet {
let rawValue: Int
static let phoneInValid = PhoneValidation(rawValue: 1 << 0)
static let phoneValid = PhoneValidation(rawValue: 1 << 1)
static let smsValidationAttempted = PhoneValidation(rawValue: 1 << 2)
static let smsValidationFailed = PhoneValidation(rawValue: 1 << 3)
static let smsValidationSuccessful = PhoneValidation(rawValue: 1 << 4) // OTP is successfully validated in backend. The field should be non-editable in this duration
static let smsValidationOTPTriggered = PhoneValidation(rawValue: 1 << 5) // OTP validation triggered. The field should be non-editable in this duration
}
class PhonesViewModel: NSCopying {
public var phoneType: PhoneNumberType = PhoneNumberType.mobile
public var phone: String?
public var code: String?
public var countryCode: String?
public var isValid : PhoneValidation?
func copy(with zone: NSZone? = nil) -> Any {
let copy = PhonesViewModel()
copy.phoneType = phoneType
copy.phone = phone
copy.code = code
copy.countryCode = countryCode
copy.isValid = isValid
return copy
}
}
As you can see above the phone model can transition between different states. The SMS validation is available for few countries and for few it is not applicable. So, I plan on setting smsValidationOTPTriggered state when SMS validation is applicable for a country and while the validation is in progress.
What I need here is, while the states smsValidationOTPTriggered or smsValidationSuccessful are set I would not want any module of the application to modify the values(phoneType, phone, code, countryCode) of the model. In other words, I would like the model to switch to a read-only mode while these 2 states are set in model and would like the module to be informed with an error or exception when a modification is attempted.
Is there a best practice already available for what I am trying to achieve here? I have searched before raising this question but did not find any. How can I achieve this?
Thanks,
Raj Pawan Gumdal
How about something like this, I think its better to use property wrappers for your case! The below is not an exact solution but can modify/change to accommodate your need
import UIKit
enum PhoneNumberType {
case mobile
}
enum PhoneValidation {
case phoneInValid
case phoneValid
case smsValidationAttempted
case smsValidationFailed
case smsValidationSuccessful
case smsValidationOTPTriggered
}
struct PhonesViewModel {
public var phoneType: PhoneNumberType = PhoneNumberType.mobile
public var phone: String?
public var code: String?
public var countryCode: String?
public var phoneValidation : PhoneValidation?
func validate(value: [PhoneValidation]) -> Bool {
//add proper check here
return false
}
}
#propertyWrapper
struct Wrapper {
private(set) var value: PhonesViewModel? = nil
var validators: [PhoneValidation] = []
var wrappedValue: PhonesViewModel? {
get { value }
set {
if let model = newValue, model.validate(value: validators) {
value = newValue
print("Value assigned")
} else {
print("Value not assigned")
}
}
}
}
struct SomeOtherClass {
#Wrapper(validators: [PhoneValidation.phoneInValid])
var model: PhonesViewModel?
}
var a = SomeOtherClass()
a.model = PhonesViewModel()
a.model = PhonesViewModel()
You can use a technique with the name "popsicle immutability". An object is initially mutable, but can be "frozen". Modifications for frozen objects are forbidden. In your case PhonesViewModel become frozen when isValid property have value smsValidationOTPTriggered or smsValidationSuccessful.
Let's add Freezable protocol for requirements to objects that can become immutable and conforming for PhonesViewModel:
protocol Freezable: class {
var isFrozen: Bool { get }
}
extension PhonesViewModel: Freezable {
var isFrozen: Bool {
isValid == .smsValidationOTPTriggered || isValid == .smsValidationSuccessful
}
}
Now we must add validation for isFrozen value when a property is assigned. It can be added in property observers like:
...
public var phone: String? {
didSet {
validate()
}
}
...
private func validate() {
assert(!isFrozen)
}
Or using property wrapper:
#propertyWrapper
struct Guarded<Value> {
private var value: Value
init(wrappedValue: Value) {
value = wrappedValue
}
#available(*, unavailable)
var wrappedValue: Value {
get { fatalError("only works on instance properties of classes that conforms to Freezable protocol") }
set { fatalError("only works on instance properties of classes that conforms to Freezable protocol") }
}
static subscript<EnclosingSelf: Freezable>(
_enclosingInstance object: EnclosingSelf,
wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Value>,
storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
) -> Value {
get {
object[keyPath: storageKeyPath].value
}
set {
precondition(!object.isFrozen, "Object \(object) is frozen! Modifications are forbidden")
object[keyPath: storageKeyPath].value = newValue
}
}
}
So your class will look like:
class PhonesViewModel: NSCopying {
#Guarded
public var phoneType: PhoneNumberType = PhoneNumberType.mobile
#Guarded
public var phone: String?
#Guarded
public var code: String?
#Guarded
public var countryCode: String?
#Guarded
public var isValid : PhoneValidation?
func copy(with zone: NSZone? = nil) -> Any {
let copy = PhonesViewModel()
copy.phoneType = phoneType
copy.phone = phone
copy.code = code
copy.countryCode = countryCode
copy.isValid = isValid
return copy
}
}
I have a couple of private properties defined like so..
private var tableConfig : TableViewConfig<Company, CompanyCell>?
private var tabledata = [Company]() {
didSet {
tableConfig?.items = tabledata
}
}
Now there are 2 other properties defined like so...
var model: Model?
var companyCell: TableviewCell?
Now, if get the value in model as Industry and the value in companyCell as IndustryCell, how can I update these values to private var tableConfig : TableViewConfig.... and private var tabledata = [Company]().... so that they will ultimately have the values like so..
private var tableConfig : TableViewConfig<Industry, IndustryCell>?
private var tabledata = [Industry]() {
didSet {
tableConfig?.items = tabledata
}
}
you can use a get set variabile to achieve this result
var _tabledata: [Industry] {
get {
return tabledata
}
set {
tabledata = newValue
}
}
As the attribute private implies properties and functions declared as private can only be accessed within the scope they are declared.
You have two options:
Change the access control to fileprivate (if the caller is in the same file) or internal or lower restriction.
Add an internal or lower restriction computed property or method in the scope of the private property to set it.
You can expose an init() or a method to set the value of private properties, i.e.
class SampleClass {
private var tableConfig : TableViewConfig<Company, CompanyCell>?
private var tabledata = [Company]() {
didSet {
tableConfig?.items = tabledata
}
}
init(tableData: [Company]) {
self.tabledata = tabledata
}
func add(item: Company) {
self.tabledata.append(item)
}
}
You can create an init in case you want to initialise your private variable and use a method in case you want to update the private variables.
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
}
}
}
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
}
}