SwiftUI: How to persist #Published variable using UserDefaults? - swiftui

Question

I want a #Published variable to be persisted, so that it's the same every time when I relaunch my app.
I want to use both the #UserDefault and #Published property wrappers on one variable. For example I need a '#PublishedUserDefault var isLogedIn'.
I have the following propertyWrapper
import Foundation
#propertyWrapper
struct UserDefault<T> {
let key: String
let defaultValue: T
init(_ key: String, defaultValue: T) {
self.key = key
self.defaultValue = defaultValue
}
var wrappedValue: T {
get {
return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
}
set {
UserDefaults.standard.set(newValue, forKey: key)
}
}
}
This is my Settings class
import SwiftUI
import Combine
class Settings: ObservableObject {
#Published var isLogedIn : Bool = false
func doLogin(params:[String:String]) {
Webservice().login(params: params) { response in
if let myresponse = response {
self.login = myresponse.login
}
}
}
}
My View class
struct HomeView : View {
#EnvironmentObject var settings: Settings
var body: some View {
VStack {
if settings.isLogedIn {
Text("Loged in")
} else{
Text("Not Loged in")
}
}
}
}
Is there a way to make a single property wrapper that covers both the persisting and the publishing?

Answer 1

import SwiftUI
import Combine
fileprivate var cancellables = [String : AnyCancellable] ()
public extension Published {
init(wrappedValue defaultValue: Value, key: String) {
let value = UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue
self.init(initialValue: value)
cancellables[key] = projectedValue.sink { val in
UserDefaults.standard.set(val, forKey: key)
}
}
}
class Settings: ObservableObject {
#Published(key: "isLogedIn") var isLogedIn = false
...
}
Sample: https://youtu.be/TXdAg_YvBNE
Version for all Codable types check out here

Answer 2

To persist your data you could use the #AppStorage property wrapper.
However, without using #Published your ObservableObject will no longer put out the news about the changed data. To fix this, simply call objectWillChange.send() from the property's willSet observer.
import SwiftUI
class Settings: ObservableObject {
#AppStorage("Example") var example: Bool = false {
willSet {
// Call objectWillChange manually since #AppStorage is not published
objectWillChange.send()
}
}
}

Answer 3

It should be possible to compose a new property wrapper:
Composition was left out of the first revision of this proposal,
because one can manually compose property wrapper types. For example,
the composition #A #B could be implemented as an AB wrapper:
#propertyWrapper
struct AB<Value> {
private var storage: A<B<Value>>
var wrappedValue: Value {
get { storage.wrappedValue.wrappedValue }
set { storage.wrappedValue.wrappedValue = newValue }
}
}
The main benefit of this approach is its predictability: the author of
AB decides how to best achieve the composition of A and B, names it
appropriately, and provides the right API and documentation of its
semantics. On the other hand, having to manually write out each of the
compositions is a lot of boilerplate, particularly for a feature whose
main selling point is the elimination of boilerplate. It is also
unfortunate to have to invent names for each composition---when I try
the compose A and B via #A #B, how do I know to go look for the
manually-composed property wrapper type AB? Or maybe that should be
BA?
Ref: Property WrappersProposal: SE-0258

Answer 4

You currently can't wrap #UserDefault around #Published since that is not currently allowed.
The way to implement #PublishedUserDefault is to pass an objectWillChange into the wrapper and call it before setting the variable.

Answer 5

struct HomeView : View {
#StateObject var auth = Auth()
#AppStorage("username") var username: String = "Anonymous"
var body: some View {
VStack {
if username != "Anonymous" {
Text("Logged in")
} else{
Text("Not Logged in")
}
}
.onAppear(){
auth.login()
}
}
}
import SwiftUI
import Combine
class Auth: ObservableObject {
func login(params:[String:String]) {
Webservice().login(params: params) { response in
if let myresponse = response {
UserDefaults.standard.set(myresponse.login, forKey: "username")`
}
}
}
}