I have an async function that purchases a subscription. It then dismisses the view via the DismissAction that was passed to it, sets a #Published value to true, and then sets the alternate app icon.
The following code doesn't work properly due to UI updates being called from an async function:
func makePurchase(dismiss: DismissAction) async throws {
let (_, purchaserInfo, _) = try await Purchases.shared.purchasePackage(selectedPackage)
dismiss() // Doesn't like this
if purchaserInfo.hasPermissions {
upgradeToUltimate() // Or this
}
}
struct SubscriptionService {
function upgradeToUltimate() {
Auth.shared.user?.isUltimate = true // This is setting a #Published that updates UI elements
if UIApplication.shared.supportsAlternateIcons,
UIApplication.shared.alternateIconName == nil {
UIApplication.shared.setAlternateIconName(Constants.AppIconNames.ultimate) // This stops my dismiss() from happening
}
}
}
So to fix this I've done the following by adding #MainActor to the first function and wrapping the second one in a DispatchQueue call. It works, but I'm just wondering if there's a better way to do this:
#MainActor
func makePurchase(dismiss: DismissAction) async throws {
let (_, purchaserInfo, _) = try await Purchases.shared.purchasePackage(selectedPackage)
dismiss()
if purchaserInfo.hasPermissions {
SubscriptionService.upgradeToUltimate()
}
}
struct SubscriptionService {
static func upgradeToUltimate() {
DispatchQueue.main.async {
Auth.shared.user?.isUltimate = true
if UIApplication.shared.supportsAlternateIcons,
UIApplication.shared.alternateIconName == nil {
UIApplication.shared.setAlternateIconName(Constants.AppIconNames.ultimate)
}
}
}
}
Interacting with the UI must only be done on the main thread/queue/actor. You've done this correctly.
Related
Say I have this code:
class Presenter {
var viewToUpdate: UIView!
func updateUI() {
viewToUpdate.backgroundColor = .red
}
}
class ShinyNewAsyncAwaitClass {
func doAsyncAwaitThing() async {
// make network call or something
}
}
class OtherClassThatICantUpdateToAsyncAwaitYet {
func doOldClosureBasedThing(completion: #escaping () -> Void) {
// make network call or something
completion()
}
}
class TheClassThatUsesAllThisStuff {
var newClass: ShinyNewAsyncAwaitClass!
var oldClass: OtherClassThatICantUpdateToAsyncAwaitYet!
var presenter: Presenter!
func doSomethingWithNewClass() {
Task {
await self.newClass.doAsyncAwaitThing()
// ---->>> What do I do here? <<<<----
await self.presenter.updateUI()
}
}
func doSomethingWithOldClass() {
oldClass.doOldClosureBasedThing {
DispatchQueue.main.async {
self.presenter.updateUI()
}
}
}
func justUpdateTheView() {
self.presenter.updateUI()
}
}
In short, I have three classes. One I can update to async/await, the other I can't, and one that uses both. Both need access to a function that updates UI, both will need to access that function on the main thread.
I saw somewhere I can add #MainActor to the updateUI function, but in cases where I'm already on the main thread and I just want to call updateUI, like in justUpdateTheView I get this error:
Call to main actor-isolated instance method 'updateUI()' in a synchronous nonisolated context
Add '#MainActor' to make instance method 'justUpdateTheView()' part of global actor 'MainActor'
I can't define justUpdateTheView as #MainActor, because we're trying to update our project to the new concurrency stuff slowly and this would cause a chain reaction of changes that need to be made.
What to do for the best? Can I do something like this:
func doSomethingWithNewClass() {
Task {
await self.newClass.doAsyncAwaitThing()
DispatchQueue.main.async {
self.presenter.updateUI()
}
}
}
It compiles, but are there any gotchas to be aware of?
You can do something like this to run the UI code on the MainActor:
func doSomethingWithNewClass() {
Task {
await self.newClass.doAsyncAwaitThing()
await MainActor.run {
self.presenter.updateUI()
}
}
}
Where is the correct place I should put the code that would trigger a loading to display in my app.
It is correct to do is on view? since it is displaying something on screen, so it fits as a UI logic
class ViewController: UIViewController {
func fetchData() {
showLoading()
interactor?.fetchData()
}
}
or on interactor? since it's a business logic. something like, everytime a request is made, we should display a loading. View only knows how to construct a loading, not when to display it.
class Interactor {
func fetchData() {
presenter?.presentLoading(true)
worker?.fetchData() { (data) [weak self] in
presenter?.presentLoading(false)
self?.presenter?.presentData(data)
}
}
}
same question applies to MVVM and MVP.
it is totally up to you . i am showing loading using an Observable .
in my viewModel there is an enum called action :
enum action {
case success(count:Int)
case deleteSuccess
case loading
case error
}
and an Observable of action type :
var actionsObservable = PublishSubject<action>()
then , before fetching data i call onNext method of actionObservable(loading)
and subscribing to it in viewController :
vm.actionsObserver
.observeOn(MainScheduler.instance)
.subscribe(onNext: { (action) in
switch action {
case .success(let count):
if(count == 0){
self.noItemLabel.isHidden = false
}
else{
self.noItemLabel.isHidden = true
}
self.refreshControl.endRefreshing()
self.removeSpinner()
case .loading:
self.showSpinner(onView : self.view)
case .error:
self.removeSpinner()
}
}, onError: { (e) in
print(e)
}).disposed(by: disposeBag)
You can use the delegate or completion handler to the update the UI from view model.
class PaymentViewController: UIViewController {
// for UI update
func showLoading() {
self.showLoader()
}
func stopLoading() {
self.removeLoader()
}
}
protocol PaymentOptionsDelegate : AnyObject {
func showLoading()
func stopLoading()
}
class PaymentOptionsViewModel {
weak var delegate : PaymentOptionsDelegate?
func fetchData() {
delegate?.showLoading()
delegate?.stopLoading()
}
}
Caveat - I read the few questions about testing threads but may have missed the answer so if the answer is there and I missed it, please point me in the right direction.
I want to test that a tableView call to reloadData is executed on the main queue.
This should code should result in a passing test:
var cats = [Cat]() {
didSet {
DispatchQueue.main.async { [weak self] in
tableView.reloadData()
}
}
}
This code should result in a failing test:
var cats = [Cat]() {
didSet {
tableView.reloadData()
}
}
What should the test look like?
Note to the testing haters: I know this is an easy thing to catch when you run the app but it's also an easy thing to miss when you're refactoring and adding layers of abstraction and multiple network calls and want to update the UI with some data but not other data etc etc... so please don't just answer with "Updates to UI go on the main thread" I know that already. Thanks!
Use dispatch_queue_set_specific function in order to associate a key-value pair with the main queue
Then use dispatch_queue_get_specific to check for the presence of key & value:
fileprivate let mainQueueKey = UnsafeMutablePointer<Void>.alloc(1)
fileprivate let mainQueueValue = UnsafeMutablePointer<Void>.alloc(1)
/* Associate a key-value pair with the Main Queue */
dispatch_queue_set_specific(
dispatch_get_main_queue(),
mainQueueKey,
mainQueueValue,
nil
)
func isMainQueue() -> Bool {
/* Checking for presence of key-value on current queue */
return (dispatch_get_specific(mainQueueKey) == mainQueueValue)
}
I wound up taking the more convoluted approach of adding an associated Bool value to UITableView, then swizzling UITableView to redirect reloadData()
fileprivate let reloadDataCalledOnMainThreadString = NSUUID().uuidString.cString(using: .utf8)!
fileprivate let reloadDataCalledOnMainThreadKey = UnsafeRawPointer(reloadDataCalledOnMainThreadString)
extension UITableView {
var reloadDataCalledOnMainThread: Bool? {
get {
let storedValue = objc_getAssociatedObject(self, reloadDataCalledOnMainThreadKey)
return storedValue as? Bool
}
set {
objc_setAssociatedObject(self, reloadDataCalledOnMainThreadKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
dynamic func _spyReloadData() {
reloadDataCalledOnMainThread = Thread.isMainThread
_spyReloadData()
}
//Then swizzle that with reloadData()
}
Then in the test I updated the cats on the background thread so I could check if they were reloaded on the main thread.
func testReloadDataIsCalledWhenCatsAreUpdated() {
// Checks for presence of another associated property that's set in the swizzled reloadData method
let reloadedPredicate = NSPredicate { [controller] _,_ in
controller.tableView.reloadDataWasCalled
}
expectation(for: reloadedPredicate, evaluatedWith: [:], handler: nil)
// Appends on the background queue to simulate an asynchronous call
DispatchQueue.global(qos: .background).async { [weak controller] in
let cat = Cat(name: "Test", identifier: 1)
controller?.cats.append(cat)
}
// 2 seconds seems excessive but NSPredicates only evaluate once per second
waitForExpectations(timeout: 2, handler: nil)
XCTAssert(controller.tableView.reloadDataCalledOnMainThread!,
"Reload data should be called on the main thread when cats are updated on a background thread")
}
Here is an updated version of the answer provided by Oleh Zayats that I am using in some tests of Combine publishers.
extension DispatchQueue {
func setAsExpectedQueue(isExpected: Bool = true) {
guard isExpected else {
setSpecific(key: .isExpectedQueueKey, value: nil)
return
}
setSpecific(key: .isExpectedQueueKey, value: true)
}
static func isExpectedQueue() -> Bool {
guard let isExpectedQueue = DispatchQueue.getSpecific(key: .isExpectedQueueKey) else {
return false
}
return isExpectedQueue
}
}
extension DispatchSpecificKey where T == Bool {
static let isExpectedQueueKey = DispatchSpecificKey<Bool>()
}
This is an example test using Dispatch and Combine to verify it is working as expected (you can see it fail if you remove the receive(on:) operator).:
final class IsExpectedQueueTests: XCTestCase {
func testIsExpectedQueue() {
DispatchQueue.main.setAsExpectedQueue()
let valueExpectation = expectation(description: "The value was received on the expected queue")
let completionExpectation = expectation(description: "The publisher completed on the expected queue")
defer {
waitForExpectations(timeout: 1)
DispatchQueue.main.setAsExpectedQueue(isExpected: false)
}
DispatchQueue.global().sync {
Just(())
.receive(on: DispatchQueue.main)
.sink { _ in
guard DispatchQueue.isExpectedQueue() else {
return
}
completionExpectation.fulfill()
} receiveValue: { _ in
guard DispatchQueue.isExpectedQueue() else {
return
}
valueExpectation.fulfill()
}.store(in: &cancellables)
}
}
override func tearDown() {
cancellables.removeAll()
super.tearDown()
}
var cancellables = Set<AnyCancellable>()
}
I'm beginning with MVVM in order to well separate logic code from the view. But I have some concern about where to put the progressHUD related code when tapping a button that makes a request.
Before, I used to do that:
//Before
#IBAction func startRequestTapped() {
SVProgressHUD.show()
self.apiClient.requestObservable().subscribe(onError: { (error) in
SVProgressHUD.hide()
}, onCompleted: {
SVProgressHUD.hide()
})
}
But when I use mvvm, I do like that:
//In the viewModel
public var validateButtonDidTap = PublishSubject<Void>()
init() {
validateButtonDidTap.flatMap { (_)
return self.apiClient.requestObservable()
}
}
// In the viewController
viewDidLoad() {
let tap = self.validateButton.rx.tap
tap.bindTo(self.viewModel.validateButtonDidTap)
}
And amongst that, I don't know where to put the the ProgressHUD hide or show.
Mark answer is right, but I am going to guide you step by step.
Let's supose you're going to try signing in.
Copy ActivityIndicator.swift file in your project.
In the viewModel:
//MARK: - Properties
/// The http client
private let apiClient: YourApiClient
/// Clousure when button is tapped
var didTappedButton: () -> Void = {}
/// The user
var user: Observable<User>
/// Is signing process in progress
let signingIn: Observable<Bool> = ActivityIndicator().asObservable()
//MARK: - Initialization
init(client: YourApiClient) {
self.client = client
self.didTappedButton = { [weak self] in
self.user = self.apiClient
.yourSignInRequest()
.trackActivity(self.signingIn)
.observeOn(MainScheduler.instance)
}
}
Create an extension of SVProgressHUD: (I don't know SVProgressHUD library, but it would be something like this. Please fix it if needed)
extension Reactive where Base: SVProgressHUD {
/// Bindable sink for `show()`, `hide()` methods.
public static var isAnimating: UIBindingObserver<Base, Bool> {
return UIBindingObserver(UIElement: self.base) { progressHUD, isVisible in
if isVisible {
progressHUD.show() // or other show methods
} else {
progressHUD.dismiss() // or other hide methods
}
}
}
}
In your viewController:
#IBAction func startRequestTapped() {
viewModel.didTappedButton()
}
override func viewDidLoad() {
// ...
viewModel.signingIn
.bindTo(SVProgressHUD.rx.isAnimating)
.addDisposableTo(disposeBag)
}
Accepted answer updated to Swift 4, RxSwift 4.0.0 and SVProgressHUD 2.2.2:
3- Extension:
extension Reactive where Base: SVProgressHUD {
public static var isAnimating: Binder<Bool> {
return Binder(UIApplication.shared) {progressHUD, isVisible in
if isVisible {
SVProgressHUD.show()
} else {
SVProgressHUD.dismiss()
}
}
}
}
4- Controller:
viewModel.signingIn.asObservable().bind(to: SVProgressHUD.rx.isAnimating).disposed(by: disposeBag)
You could try using an ActivityIndicator.
See the example here:
https://github.com/RxSwiftCommunity/RxSwiftUtilities
I am currently having an issue with multiple network requests executing when using RxSwift Observables. I understand that if one creates a cold observable and it has multiple observers, the observable will execute its block each time it is subscribed to.
I have tried to create a shared subscription observable that executes the network request once, and multiple subscribers will be notified of the result. Below is the what I have tried.
Sequence of events
Create the view model with the tap event of a uibutton
Create the serviceStatus Observable as a public property on the view model. This Observable is mapped from the buttonTapped Observable. It then filters out the "Loading" status. The returned Observable has a shareReplay(1) executed on it to return a shared subscription.
Create the serviceExecuting Observable as a public property on the view model. This observable is mapped from the serviceStatus Observable. It will return true if the status is "Loading"
Bind the uilabel to the serviceStatus Observable
Bind the activity indicator to the serviceExecuting Observable.
When the button is tapped, the service request is executed three time where I would be expecting it to be executed only once. Does anything stand out as incorrect?
Code
class ViewController {
let disposeBag = DisposeBag()
var button: UIButton!
var resultLabel: UILabel!
var activityIndicator: UIActivityIndicator!
lazy var viewModel = { // 1
return ViewModel(buttonTapped: self.button.rx.tap.asObservable())
}
override func viewDidLoad() {
super.viewDidLoad()
self.viewModel.serviceStatus.bindTo(self.resultLabel.rx_text).addDispsoableTo(disposeBag) // 4
self.viewModel.serviceExecuting.bindTo(self.activityIndicator.rx_animating).addDispsoableTo(disposeBag) // 5
}
}
class ViewModel {
public var serviceStatus: Observable<String> { // 2
let serviceStatusObseravble = self.getServiceStatusObservable()
let filtered = serviceStatusObseravble.filter { status in
return status != "Loading"
}
return filtered
}
public var serviceExecuting: Observable<Bool> { // 3
return self.serviceStatus.map { status in
return status == "Loading"
}
.startWith(false)
}
private let buttonTapped: Observable<Void>
init(buttonTapped: Observable<Void>) {
self.buttonTapped = buttonTapped
}
private func getServiceStatusObservable() -> Observable<String> {
return self.buttonTapped.flatMap { _ -> Observable<String> in
return self.createServiceStatusObservable()
}
}
private func createServiceStatusObservable() -> Observable<String> {
return Observable.create({ (observer) -> Disposable in
someAsyncServiceRequest() { result }
observer.onNext(result)
})
return NopDisposable.instance
})
.startWith("Loading")
.shareReplay(1)
}
EDIT:
Based on the conversation below, the following is what I was looking for...
I needed to apply a share() function on the Observable returned from the getServiceStatusObservable() method and not the Observable returned from the createServiceStatusObservable() method. There were multiple observers being added to this observable to inspect the current state. This meant that the observable executing the network request was getting executed N times (N being the number of observers). Now every time the button is tapped, the network request is executed once which is what I needed.
private func getServiceStatusObservable() -> Observable<String> {
return self.buttonTapped.flatMap { _ -> Observable<String> in
return self.createServiceStatusObservable()
}.share()
}
.shareReplay(1) will apply to only one instance of the observable. When creating it in createServiceStatusObservable() the sharing behavior will only affect the one value returned by this function.
class ViewModel {
let serviceStatusObservable: Observable<String>
init(buttonTapped: Observable<Void>) {
self.buttonTapped = buttonTapped
self.serviceStatusObservable = Observable.create({ (observer) -> Disposable in
someAsyncServiceRequest() { result in
observer.onNext(result)
}
return NopDisposable.instance
})
.startWith("Loading")
.shareReplay(1)
}
private func getServiceStatusObservable() -> Observable<String> {
return self.buttonTapped.flatMap { [weak self] _ -> Observable<String> in
return self.serviceStatusObservable
}
}
}
With this version, serviceStatusObservable is only created once, hence it's side effect will be shared everytime it is used, as it is the same instance.