When to use @objc attribute?

The @objc attribute in Swift is used to expose Swift code to the Objective-C runtime, making it accessible from Objective-C. This is particularly important for interoperability between Swift and Objective-C, which is common in iOS development due to the extensive use of Objective-C in many existing frameworks and libraries.

Here are the key scenarios when you should use the @objc attribute:

1. Interacting with Objective-C APIs: If you need to call Swift methods from Objective-C code, you must mark those methods with @objc. This is essential when working with APIs that are written in Objective-C, such as many parts of UIKit and other Apple frameworks[1][2][5].

   swift Copy

   @objc func greet() {
       print("Hello, world!")
   }

2. Using Objective-C Features: Some features, like selectors, Key-Value Observing (KVO), and Key-Value Coding (KVC), are specific to Objective-C. To use these features with Swift methods, you need to mark them with @objc[2][3].

   swift Copy

   @objc private func doubleTapGestureRecognized(recognizer: UITapGestureRecognizer) {
       // Handle double tap
   }

3. Dynamic Dispatch: If you need dynamic dispatch, which is a feature of the Objective-C runtime, you should use @objc dynamic. This is often used in conjunction with KVO or when you need to override methods dynamically at runtime[3].

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   @objc dynamic func performOperation() -> Int {
       return 42
   }

4. Customizing Objective-C Names: You can use @objc to provide custom names for Swift methods or properties when they are exposed to Objective-C. This can help maintain consistency with Objective-C naming conventions[4].

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   @objc(sharedManager)
   static let shared = MyManager()

5. Exposing Entire Classes: If you want to expose all members of a class to Objective-C, you can use the @objcMembers attribute on the class. This automatically applies @objc to all members of the class, its extensions, and its subclasses[1][6].

   swift Copy

   @objcMembers class Gr...