I have a problem from Protocol oriented ViewModels.
I have two very similar pages,so i made a baseController and baseViewModel to put shared properties and methods. And made two other controllers and viewModels for two pages.
And I made a protocol to define the properties and methods.
My baseController has var viewModel: BaseViewModelProtocol .
But my other two controller cannot use the properties and methods from their viewModel, it's says
Value of type 'BaseViewModelProtocol?' has no member ''
ViewModel1 is for Controller1, ViewModel2 is for Controller2, here is my example
protocol BaseViewModelProtocol {
var name: String { get }
func reset()
}
class BaseViewModel: BaseViewModelProtocol {
func reset() { }
}
class ViewModel1: BaseViewModel {
var score: Int = 0
func someMethods() {}
}
class ViewModel2: BaseViewModel {
var money: Int = 1000
func something() {
print("something")
}
}
class BaseViewController: UIViewController {
var viewModel: BaseViewModelProtocol?
init(viewModel: BaseViewModelProtocol) {
self.viewModel = viewModel
super.init(nibName: nil, bundle: nil)
}
}
class ViewController1: BaseViewController {
override func viewDidLoad() {
super.viewDidLoad()
print(viewModel?.score) //it is error!!!!
}
}
When i init the Controller, i Cannot use any properties and methods from ViewModel2, and the same like controller1.
class ViewController2: BaseOrderViewController {
override func viewDidLoad() {
super.viewDidLoad()
viewModel?.something(). //it is error!!!!
}
}
how to my protocol oriented viewModel?
After reading your post I feel like there is too many things that should be addressed here.
You are trying to ask something before understanding important characteristics of the Object Oriented Programmation paradigm. I recommend you to try and search information about class abstraction, composition vs inheritance and specificaly how to use the protocols in Swift.
Maybe you could start with https://cocoacasts.com/how-to-create-an-abstract-class-in-swift.
Even so, i am going to try to point out some issues in your code.
Seems like you tried to "hide" your source code by changing your classes and properties' names. The way it's done makes it harder to read, understand and introduces mistakes.
Inheriting from another class:
class ViewModel1: BaseViewModel
it's not the same as inheriting from a protocol:
class BaseViewModel: BaseViewModelProtocol
while the first one provides you a default implementation of a method that can be overrided, the second, doesn't. So it is mandatory to provide the implementation of the method in every class that inherits the protocol.
Note that the BaseViewController has a property with type BaseViewModelProtocol. That protocol doesn't have a method called "something" neither can inherit that function from another. It's within reason that the compiler shows the error.
If you want to use "something" from a Class that inherits BaseViewController, you have many ways. You could change the type of the viewModel in the BaseViewController to BaseViewModel after adding there an implementation of "something". You could also add the function to the protocol and make sure that it's implemented in all of the classes which inherit the protocol...
I hope I have helped you.
I'm trying to work out an appropriate singleton model for usage in Swift. So far, I've been able to get a non-thread safe model working as:
class var sharedInstance: TPScopeManager {
get {
struct Static {
static var instance: TPScopeManager? = nil
}
if !Static.instance {
Static.instance = TPScopeManager()
}
return Static.instance!
}
}
Wrapping the singleton instance in the Static struct should allow a single instance that doesn't collide with singleton instances without complex naming schemings, and it should make things fairly private. Obviously though, this model isn't thread-safe. So I tried to add dispatch_once to the whole thing:
class var sharedInstance: TPScopeManager {
get {
struct Static {
static var instance: TPScopeManager? = nil
static var token: dispatch_once_t = 0
}
dispatch_once(Static.token) { Static.instance = TPScopeManager() }
return Static.instance!
}
}
But I get a compiler error on the dispatch_once line:
Cannot convert the expression's type 'Void' to type '()'
I've tried several different variants of the syntax, but they all seem to have the same results:
dispatch_once(Static.token, { Static.instance = TPScopeManager() })
What is the proper usage of dispatch_once using Swift? I initially thought the problem was with the block due to the () in the error message, but the more I look at it, the more I think it may be a matter of getting the dispatch_once_t correctly defined.
tl;dr: Use the class constant approach if you are using Swift 1.2 or above and the nested struct approach if you need to support earlier versions.
From my experience with Swift there are three approaches to implement the Singleton pattern that support lazy initialization and thread safety.
Class constant
class Singleton {
static let sharedInstance = Singleton()
}
This approach supports lazy initialization because Swift lazily initializes class constants (and variables), and is thread safe by the definition of let. This is now officially recommended way to instantiate a singleton.
Class constants were introduced in Swift 1.2. If you need to support an earlier version of Swift, use the nested struct approach below or a global constant.
Nested struct
class Singleton {
class var sharedInstance: Singleton {
struct Static {
static let instance: Singleton = Singleton()
}
return Static.instance
}
}
Here we are using the static constant of a nested struct as a class constant. This is a workaround for the lack of static class constants in Swift 1.1 and earlier, and still works as a workaround for the lack of static constants and variables in functions.
dispatch_once
The traditional Objective-C approach ported to Swift. I'm fairly certain there's no advantage over the nested struct approach but I'm putting it here anyway as I find the differences in syntax interesting.
class Singleton {
class var sharedInstance: Singleton {
struct Static {
static var onceToken: dispatch_once_t = 0
static var instance: Singleton? = nil
}
dispatch_once(&Static.onceToken) {
Static.instance = Singleton()
}
return Static.instance!
}
}
See this GitHub project for unit tests.
Since Apple has now clarified that static struct variables are initialized both lazy and wrapped in dispatch_once (see the note at the end of the post), I think my final solution is going to be:
class WithSingleton {
class var sharedInstance: WithSingleton {
struct Singleton {
static let instance = WithSingleton()
}
return Singleton.instance
}
}
This takes advantage of the automatic lazy, thread-safe initialization of static struct elements, safely hides the actual implementation from the consumer, keeps everything compactly compartmentalized for legibility, and eliminates a visible global variable.
Apple has clarified that lazy initializer are thread-safe, so there's no need for dispatch_once or similar protections
The lazy initializer for a global variable (also for static members of structs and enums) is run the first time that global is accessed, and is launched as dispatch_once to make sure that the initialization is atomic. This enables a cool way to use dispatch_once in your code: just declare a global variable with an initializer and mark it private.
From here
For Swift 1.2 and beyond:
class Singleton {
static let sharedInstance = Singleton()
}
With a proof of correctness (all credit goes here), there is little to no reason now to use any of the previous methods for singletons.
Update: This is now the official way to define singletons as described in the official docs!
As for concerns on using static vs class. static should be the one to use even when class variables become available. Singletons are not meant to be subclassed since that would result in multiple instances of the base singleton. Using static enforces this in a beautiful, Swifty way.
For Swift 1.0 and 1.1:
With the recent changes in Swift, mostly new access control methods, I am now leaning towards the cleaner way of using a global variable for singletons.
private let _singletonInstance = SingletonClass()
class SingletonClass {
class var sharedInstance: SingletonClass {
return _singletonInstance
}
}
As mentioned in the Swift blog article here:
The lazy initializer for a global variable (also for static members of
structs and enums) is run the first time that global is accessed, and
is launched as dispatch_once to make sure that the initialization is
atomic. This enables a cool way to use dispatch_once in your code:
just declare a global variable with an initializer and mark it
private.
This way of creating a singleton is thread safe, fast, lazy, and also bridged to ObjC for free.
Swift 1.2 or later now supports static variables/constants in classes. So you can just use a static constant:
class MySingleton {
static let sharedMySingleton = MySingleton()
private init() {
// ...
}
}
There is a better way to do it. You can declare a global variable in your class above the class declaration like this:
var tpScopeManagerSharedInstance = TPScopeManager()
This just calls your default init or whichever init and global variables are dispatch_once by default in Swift. Then in whichever class you want to get a reference, you just do this:
var refrence = tpScopeManagerSharedInstance
// or you can just access properties and call methods directly
tpScopeManagerSharedInstance.someMethod()
So basically you can get rid of the entire block of shared instance code.
Swift singletons are exposed in the Cocoa frameworks as class functions, e.g. NSFileManager.defaultManager(), NSNotificationCenter.defaultCenter(). So it makes more sense as a class function to mirror this behavior, rather than a class variable as some other solutions. e.g:
class MyClass {
private static let _sharedInstance = MyClass()
class func sharedInstance() -> MyClass {
return _sharedInstance
}
}
Retrieve the singleton via MyClass.sharedInstance().
Per the Apple documentation, it has been repeated many times that the easiest way to do this in Swift is with a static type property:
class Singleton {
static let sharedInstance = Singleton()
}
However, if you're looking for a way to perform additional setup beyond a simple constructor call, the secret is to use an immediately invoked closure:
class Singleton {
static let sharedInstance: Singleton = {
let instance = Singleton()
// setup code
return instance
}()
}
This is guaranteed to be thread-safe and lazily initialized only once.
Swift 4+
protocol Singleton: class {
static var sharedInstance: Self { get }
}
final class Kraken: Singleton {
static let sharedInstance = Kraken()
private init() {}
}
Looking at Apple's sample code I came across this pattern. I'm not sure how Swift deals with statics, but this would be thread safe in C#. I include both the property and method for Objective-C interop.
struct StaticRank {
static let shared = RankMapping()
}
class func sharedInstance() -> RankMapping {
return StaticRank.shared
}
class var shared:RankMapping {
return StaticRank.shared
}
In brief,
class Manager {
static let sharedInstance = Manager()
private init() {}
}
You may want to read Files and Initialization
The lazy initializer for a global variable (also for static members of
structs and enums) is run the first time that global is accessed, and
is launched as dispatch_once to make sure that the initialization is
atomic.
If you are planning on using your Swift singleton class in Objective-C, this setup will have the compiler generate appropriate Objective-C-like header(s):
class func sharedStore() -> ImageStore {
struct Static {
static let instance : ImageStore = ImageStore()
}
return Static.instance
}
Then in Objective-C class you can call your singleton the way you did it in pre-Swift days:
[ImageStore sharedStore];
This is just my simple implementation.
First solution
let SocketManager = SocketManagerSingleton();
class SocketManagerSingleton {
}
Later in your code:
func someFunction() {
var socketManager = SocketManager
}
Second solution
func SocketManager() -> SocketManagerSingleton {
return _SocketManager
}
let _SocketManager = SocketManagerSingleton();
class SocketManagerSingleton {
}
And later in your code you will be able to keep braces for less confusion:
func someFunction() {
var socketManager = SocketManager()
}
final class MySingleton {
private init() {}
static let shared = MySingleton()
}
Then call it;
let shared = MySingleton.shared
Use:
class UtilSingleton: NSObject {
var iVal: Int = 0
class var shareInstance: UtilSingleton {
get {
struct Static {
static var instance: UtilSingleton? = nil
static var token: dispatch_once_t = 0
}
dispatch_once(&Static.token, {
Static.instance = UtilSingleton()
})
return Static.instance!
}
}
}
How to use:
UtilSingleton.shareInstance.iVal++
println("singleton new iVal = \(UtilSingleton.shareInstance.iVal)")
The best approach in Swift above 1.2 is a one-line singleton, as -
class Shared: NSObject {
static let sharedInstance = Shared()
private override init() { }
}
To know more detail about this approach you can visit this link.
From Apple Docs (Swift 3.0.1),
You can simply use a static type property, which is guaranteed to be
lazily initialized only once, even when accessed across multiple
threads simultaneously:
class Singleton {
static let sharedInstance = Singleton()
}
If you need to perform additional setup beyond initialization, you can
assign the result of the invocation of a closure to the global
constant:
class Singleton {
static let sharedInstance: Singleton = {
let instance = Singleton()
// setup code
return instance
}()
}
I would suggest an enum, as you would use in Java, e.g.
enum SharedTPScopeManager: TPScopeManager {
case Singleton
}
Just for reference, here is an example Singleton implementation of Jack Wu/hpique's Nested Struct implementation. The implementation also shows how archiving could work, as well as some accompanying functions. I couldn't find this complete of an example, so hopefully this helps somebody!
import Foundation
class ItemStore: NSObject {
class var sharedStore : ItemStore {
struct Singleton {
// lazily initiated, thread-safe from "let"
static let instance = ItemStore()
}
return Singleton.instance
}
var _privateItems = Item[]()
// The allItems property can't be changed by other objects
var allItems: Item[] {
return _privateItems
}
init() {
super.init()
let path = itemArchivePath
// Returns "nil" if there is no file at the path
let unarchivedItems : AnyObject! = NSKeyedUnarchiver.unarchiveObjectWithFile(path)
// If there were archived items saved, set _privateItems for the shared store equal to that
if unarchivedItems {
_privateItems = unarchivedItems as Array<Item>
}
delayOnMainQueueFor(numberOfSeconds: 0.1, action: {
assert(self === ItemStore.sharedStore, "Only one instance of ItemStore allowed!")
})
}
func createItem() -> Item {
let item = Item.randomItem()
_privateItems.append(item)
return item
}
func removeItem(item: Item) {
for (index, element) in enumerate(_privateItems) {
if element === item {
_privateItems.removeAtIndex(index)
// Delete an items image from the image store when the item is
// getting deleted
ImageStore.sharedStore.deleteImageForKey(item.itemKey)
}
}
}
func moveItemAtIndex(fromIndex: Int, toIndex: Int) {
_privateItems.moveObjectAtIndex(fromIndex, toIndex: toIndex)
}
var itemArchivePath: String {
// Create a filepath for archiving
let documentDirectories = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)
// Get the one document directory from that list
let documentDirectory = documentDirectories[0] as String
// append with the items.archive file name, then return
return documentDirectory.stringByAppendingPathComponent("items.archive")
}
func saveChanges() -> Bool {
let path = itemArchivePath
// Return "true" on success
return NSKeyedArchiver.archiveRootObject(_privateItems, toFile: path)
}
}
And if you didn't recognize some of those functions, here is a little living Swift utility file I've been using:
import Foundation
import UIKit
typealias completionBlock = () -> ()
extension Array {
func contains(#object:AnyObject) -> Bool {
return self.bridgeToObjectiveC().containsObject(object)
}
func indexOf(#object:AnyObject) -> Int {
return self.bridgeToObjectiveC().indexOfObject(object)
}
mutating func moveObjectAtIndex(fromIndex: Int, toIndex: Int) {
if ((fromIndex == toIndex) || (fromIndex > self.count) ||
(toIndex > self.count)) {
return
}
// Get object being moved so it can be re-inserted
let object = self[fromIndex]
// Remove object from array
self.removeAtIndex(fromIndex)
// Insert object in array at new location
self.insert(object, atIndex: toIndex)
}
}
func delayOnMainQueueFor(numberOfSeconds delay:Double, action closure:()->()) {
dispatch_after(
dispatch_time(
DISPATCH_TIME_NOW,
Int64(delay * Double(NSEC_PER_SEC))
),
dispatch_get_main_queue()) {
closure()
}
}
In swift, you can create a singleton class following way:
class AppSingleton: NSObject {
//Shared instance of class
static let sharedInstance = AppSingleton()
override init() {
super.init()
}
}
I prefer this implementation:
class APIClient {
}
var sharedAPIClient: APIClient = {
return APIClient()
}()
extension APIClient {
class func sharedClient() -> APIClient {
return sharedAPIClient
}
}
My way of implementation in Swift...
ConfigurationManager.swift
import Foundation
let ConfigurationManagerSharedInstance = ConfigurationManager()
class ConfigurationManager : NSObject {
var globalDic: NSMutableDictionary = NSMutableDictionary()
class var sharedInstance:ConfigurationManager {
return ConfigurationManagerSharedInstance
}
init() {
super.init()
println ("Config Init been Initiated, this will be called only onece irrespective of many calls")
}
Access the globalDic from any screen of the application by the below.
Read:
println(ConfigurationManager.sharedInstance.globalDic)
Write:
ConfigurationManager.sharedInstance.globalDic = tmpDic // tmpDict is any value that to be shared among the application
The only right approach is below.
final class Singleton {
static let sharedInstance: Singleton = {
let instance = Singleton()
// setup code if anything
return instance
}()
private init() {}
}
To Access
let signleton = Singleton.sharedInstance
Reasons:
static type property is guaranteed to be lazily initialized only once, even when accessed across multiple threads simultaneously, so no need of using dispatch_once
Privatising the init method so instance can't be created by other classes.
final class as you do not want other classes to inherit Singleton class.
After seeing David's implementation, it seems like there is no need to have a singleton class function instanceMethod since let is doing pretty much the same thing as a sharedInstance class method. All you need to do is declare it as a global constant and that would be it.
let gScopeManagerSharedInstance = ScopeManager()
class ScopeManager {
// No need for a class method to return the shared instance. Use the gScopeManagerSharedInstance directly.
}
func init() -> ClassA {
struct Static {
static var onceToken : dispatch_once_t = 0
static var instance : ClassA? = nil
}
dispatch_once(&Static.onceToken) {
Static.instance = ClassA()
}
return Static.instance!
}
Swift to realize singleton in the past, is nothing more than the three ways: global variables, internal variables and dispatch_once ways.
Here are two good singleton.(note: no matter what kind of writing will must pay attention to the init () method of privatisation.Because in Swift, all the object's constructor default is public, needs to be rewritten init can be turned into private, prevent other objects of this class '()' by default initialization method to create the object.)
Method 1:
class AppManager {
private static let _sharedInstance = AppManager()
class func getSharedInstance() -> AppManager {
return _sharedInstance
}
private init() {} // Privatizing the init method
}
// How to use?
AppManager.getSharedInstance()
Method 2:
class AppManager {
static let sharedInstance = AppManager()
private init() {} // Privatizing the init method
}
// How to use?
AppManager.sharedInstance
Swift 5.2
You can point to the type with Self. So:
static let shared = Self()
And should be inside a type, like:
class SomeTypeWithASingletonInstance {
static let shared = Self()
}
This is the simplest one with thread safe capabilities. No other thread can access the same singleton object even if they want. Swift 3/4
struct DataService {
private static var _instance : DataService?
private init() {} //cannot initialise from outer class
public static var instance : DataService {
get {
if _instance == nil {
DispatchQueue.global().sync(flags: .barrier) {
if _instance == nil {
_instance = DataService()
}
}
}
return _instance!
}
}
}
I required my singleton to allow inheritance, and none of these solutions actually allowed it. So I came up with this:
public class Singleton {
private static var sharedInstanceVar = Singleton()
public class func sharedInstance() -> Singleton {
return sharedInstanceVar
}
}
public class SubSingleton: Singleton {
private static var sharedInstanceToken: dispatch_once_t = 0
public class override func sharedInstance() -> SubSingleton {
dispatch_once(&sharedInstanceToken) {
sharedInstanceVar = SubSingleton()
}
return sharedInstanceVar as! SubSingleton
}
}
This way when doing Singleton.sharedInstance() first it will return the instance of Singleton
When doing SubSingleton.sharedInstance() first it will return the instance of SubSingleton created.
If the above is done, then SubSingleton.sharedInstance() is Singleton is true and the same instance is used.
The issue with this first dirty approach is that I cannot guarantee that subclasses would implement the dispatch_once_t and make sure that sharedInstanceVar is only modified once per class.
I will try to refine this further, but it would be interesting to see if anyone has strong feelings against this (besides the fact that it is verbose and requires to manually update it).
This is my implementation. It also prevents the programmer from creating a new instance:
let TEST = Test()
class Test {
private init() {
// This is a private (!) constructor
}
}
I use the following syntax:
public final class Singleton {
private class func sharedInstance() -> Singleton {
struct Static {
//Singleton instance.
static let sharedInstance = Singleton()
}
return Static.sharedInstance
}
private init() { }
class var instance: Singleton {
return sharedInstance()
}
}
This works from Swift 1.2 up to 4, and has several advantages:
Reminds the user not to subclass implementation
Prevents creation of additional instances
Ensures lazy creation and unique instantiation
Shortens syntax (avoids ()) by allowing to access instance as Singleton.instance
I need to implement a WatchKit force-touch MenuItem to call a saveWorkout() method that is located in a separate class that does not subclass WKInterfaceController.
I realize that every class needs at least one designated initializer. I am guessing this is the key?
Btw, my "saveSession() reached" print statement logs to the console when using the sim but not when I use a device. All other print statements log to the console even when using the device. A bit odd.
My attempts at initialization throw various errors such as:
1.fatal error: use of unimplemented initializer 'init()' for class 'DashboardController'
2.Missing argument for parameter 'context' in call
Dashboard.swift
class DashboardController: WKInterfaceController {
#IBOutlet var timerLabel: WKInterfaceTimer!
#IBOutlet weak var milesLabel: WKInterfaceLabel!
// var wSM: WorkoutSessionManager
//init(wSM: WorkoutSessionManager) {
// self.wSM = wSM
// super.init()
// }
override func awakeWithContext(context: AnyObject?) {
super.awakeWithContext(context)
addMenuItemWithItemIcon(.Accept, title: "Save", action: #selector(DashboardController.saveSession))
}
override func willActivate() {
super.willActivate()
print("Dashboard controller reached")
}
func saveSession() {
//wSM.saveWorkout()
print("saveSession() reached")
}
WorkoutSessionManager.swift
class WorkoutSessionContext {
let healthStore: HKHealthStore
let activityType: HKWorkoutActivityType
let locationType: HKWorkoutSessionLocationType
init(healthStore: HKHealthStore, activityType: HKWorkoutActivityType = .Other, locationType: HKWorkoutSessionLocationType = .Unknown) {
self.healthStore = healthStore
self.activityType = activityType
self.locationType = locationType
}
}
protocol WorkoutSessionManagerDelegate: class {
// ... protocol methods
}
class WorkoutSessionManager: NSObject, HKWorkoutSessionDelegate {
let healthStore: HKHealthStore
let workoutSession: HKWorkoutSession
init(context: WorkoutSessionContext) {
self.healthStore = context.healthStore
self.workoutSession = HKWorkoutSession(activityType: context.activityType, locationType: context.locationType)
self.currentActiveEnergyQuantity = HKQuantity(unit: self.energyUnit, doubleValue: 0.0)
self.currentDistanceQuantity = HKQuantity(unit: self.distanceUnit, doubleValue: 0.0)
super.init()
self.workoutSession.delegate = self
}
func saveWorkout() {
guard let startDate = self.workoutStartDate, endDate = self.workoutEndDate else {return}
// ...code...
The fatal error is (or was) caused by this line:
let wSM = WorkoutSessionManager()
That line creates a new instance of WorkoutSessionManager and calls init() on it.
Swift provides a default initializer called init() for any structure or class that provides default values for all of its properties and does not provide at least one initializer itself. But WorkoutSessionManager does not provide default values for the healthStore and workoutSession properties (and those properties are not optionals), and it provides its own initializer named init(context:), so it has no default initializer.
You need to either create your instance of WorkoutSessionManager using the designated initializer init(context:) (passing an appropriate instance of WorkoutSessionContext) or provide a default initializer for WorkoutSessionManager named init().
The precise manner in which you should do the former depends on the implementation of the rest of your app and the presentation of your DashboardController. I assume you are trying to recreate the "Fit" app shown in WWDC 2015 Session 203.
In that demonstration, the initial controller is an instance of ActivityInterfaceController, and that controller is responsible for presenting the next interface (via segues created in the storyboard). You can see the following code in the ActivityInterfaceController class:
override func contextForSegueWithIdentifier(segueIdentifier: String) -> AnyObject? {
let activityType: HKWorkoutActivityType
switch segueIdentifier {
case "Running":
activityType = .Running
case "Walking":
activityType = .Walking
case "Cycling":
activityType = .Cycling
default:
activityType = .Other
}
return WorkoutSessionContext(healthStore: self.healthStore, activityType: activityType)
}
The function above creates and returns a new instance of WorkoutSessionContext using an instance of HKHealthStore held by the initial controller. The context returned by that function is passed to the destination interface controller for the relevant segue through awakeWithContext.
For transitions in code, you can pass a context instance using equivalent functions such as pushControllerWithName(context:) which also lead to awakeWithContext.
If your initial controller is similar to the above, you can access the passed context in awakeWithContext in your DashboardController class and use it to configure a new instance of WorkoutSessionManager:
class DashboardController: WKInterfaceController
{
// ...
var wSM: WorkoutSessionManager?
override func awakeWithContext(context: AnyObject?) {
super.awakeWithContext(context)
if context is WorkoutSessionContext {
wSM = WorkoutSessionManager(context: context as! WorkoutSessionContext)
}
addMenuItemWithItemIcon(.Accept, title: "Save", action: #selector(DashboardController.saveSession))
}
// ...
}
Creating an instance of WorkoutSessionManager in that way avoids calling the (non-existent) init() initializer and permits reuse of the HKHealthStore instance. Whether that approach is open to you depends on the rest of your code and the way you are presenting your DashboardController.
Note that you should avoid creating multiple instances of WorkoutSessionManager. Use a singleton to provide a single instance of WorkoutSessionManager that is shared across your extension.