Merge branch 'main' of https://github.com/janeshsutharios/iOS_Tutorials

Author: janeshsutharios

SwiftUIExamples/MigrationGuideSwift6.swift

@@ -0,0 +1,194 @@
+// Some tips before starts
+Prefer Value Types (Structs) When Possible
+Value types are copied when passed around, reducing the risk of shared mutable state.
+
+// MARK: Example 1 
+class HomeViewControllerLegacy {
+
+    private var loadingView = UIView() // Error here `Main actor-isolated default value in a nonisolated context`
+    var hasLaunched = false
+    
+    @MainActor
+     func home() {
+        self.hasLaunched = true
+    }
+}
+
+// To solve it - initializing the view at declaration time, so you can safely create it in viewDidLoad() which runs on the main thread.
+class HomeViewControllerNew: UIViewController {
+    private var loadingView: UIView!
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        loadingView = UIView()
+        loadingView.backgroundColor = .gray
+        view.addSubview(loadingView)
+    }
+}
+
+// MARK: Example 2 Passing closure as a 'sending' parameter risks causing data races 
+class LoggerLegacy {
+    var logs: [String] = []
+
+    func log(_ message: String) {
+        logs.append(message)
+    }
+}
+struct WorkerLegacy {
+    let logger: Logger
+
+    func doWork() {
+        Task {//<<-- Error Passing closure as a 'sending' parameter risks causing data races between code in the current task and concurrent execution of the closure
+            logger.log("Work started") 
+        }
+    }
+}
+
+//-> If you know there is no data race in your codebase & want to skip data race use @preconcurrency
+@preconcurrency
+class LoggerNew {
+    var logs: [String] = []
+
+    func log(_ message: String) {
+        logs.append(message)
+    }
+}
+
+extension LoggerNew: @unchecked Sendable {}
+
+struct WorkerNew {
+    let logger: LoggerNew
+
+    func doWork() {
+        Task {
+            logger.log("Work started") // ✅ No error now
+        }
+    }
+}
+
+// MARK: Example # Trying to access heightConstraint from background thread.
+
+class ProfileViewControllerLegacy: UIViewController {
+    var heightConstraint: NSLayoutConstraint!
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        DispatchQueue.global().async {
+            // ❌ This is a background thread!
+            // ❌ Call to main actor-isolated instance method 'constraint(equalToConstant:)' in a synchronous nonisolated context
+            self.heightConstraint = self.view.heightAnchor.constraint(equalToConstant: 0)
+            self.heightConstraint.isActive = true
+        }
+    }
+}
+
+// Solution ->
+class ProfileViewControllerNew: UIViewController {
+    var heightConstraint: NSLayoutConstraint!
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        // Simulate background work
+        DispatchQueue.global().async {
+            // ✅ Launch a Swift concurrency task from background by using MainActor
+            Task { @MainActor in
+                self.heightConstraint = self.view.heightAnchor.constraint(equalToConstant: 0)
+                self.heightConstraint.isActive = true
+            }
+        }
+    }
+}
+
+// MARK: Example #4 UI Updates from Background Threads
+class CartView {
+    
+    @IBOutlet var label: UILabel!
+
+     // Error version
+    func addItemLegacy() {
+        DispatchQueue.global().async {
+            // Error here # Main actor-isolated property 'text' can not be mutated from a Sendable closure
+            self.label.text = "Updated"
+        }
+    }
+
+     // Fix version
+    func addItemFixed() {
+        Task { @MainActor in
+            self.label.text = "Updated"
+        }
+    }
+
+}
+
+// MARK: Example #5 Accessing Non-Sendable Types Across Threads
+class SongClassLegacy {
+    var data: String = ""
+    
+    func update() {
+        DispatchQueue.global().async {
+            // Warning here Capture of 'self' with non-sendable type 'SongClass' in a '@Sendable' closure
+            // Warning Class 'SongClass' does not conform to the 'Sendable' protocol
+            self.data.append("New")
+        }
+    }
+}
+
+actor SongClassNew {
+    private var data = ""
+
+    func append(_ value: String) {
+        data.append(value)
+    }
+
+    func getData() -> String {
+        return data
+    }
+}
+
+// MARK: Example #6 sendable examples
+final class SteelFactoryLegacy {
+    // Closure to be called after background work
+    var onUpdate: (() -> Void)?
+    
+    func performWork() {
+        DispatchQueue.global().async { [weak self] in
+            // Simulate background work
+            sleep(1)
+            // Warning Capture of 'self' with non-sendable type 'SteelFactoryLegacy?' in a '@Sendable' closure
+            self?.onUpdate?()
+            
+        }
+    }
+}
+
+
+final class SteelFactoryNew {
+    // Closure that can be safely called from concurrent contexts
+    var onUpdate: (@Sendable () -> Void)?
+
+    func performWork() {
+        DispatchQueue.global().async { [onUpdate] in
+            // Simulate background work
+            sleep(1)
+
+            // Safely call the closure
+            onUpdate?()
+        }
+    }
+}
+// Usage -
+class CompanyOffice {
+    
+    func getInfo() {
+        let manager = SteelFactoryNew()
+        manager.onUpdate = { [message = "Update received!"] in
+            print(message)
+        }
+        manager.performWork()
+
+    }
+}
+