• @objc vs @objc dynamic官方解释


    Some Objective-C APIs—like target-action—accept method or property names as parameters, then use those names to dynamically call or access the methods or properties. In Swift, you use the #selector and #keyPath expressions to represent those method or property names as selectors or key paths, respectively.

    https://developer.apple.com/documentation/swift/using_objective-c_runtime_features_in_swift

    一、@objc应用于函数是为了能够让函数表达为 #selector;

    In Objective-C, a selector is a type that refers to the name of an Objective-C method. In Swift, Objective-C selectors are represented by the Selector structure, and you create them using the #selector expression.

    import UIKit

    class MyViewController: UIViewController {

        let myButton = UIButton(frame: CGRect(x: 0, y: 0, 100, height: 50))

        

        override init(nibName nibNameOrNil: NSNib.Name?, bundle nibBundleOrNil: Bundle?) {

            super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)

            let action = #selector(MyViewController.tappedButton)

            myButton.addTarget(self, action: action, forControlEvents: .touchUpInside)

        }

        

        @objc func tappedButton(_ sender: UIButton?) {

            print("tapped button")

        }

        

        required init?(coder: NSCoder) {

            super.init(coder: coder)

        }

    二、@objc应用于变量是为了能够让变量表达为keypath字符串,进而使用kvc功能。

    class Person: NSObject {

        @objc var name: String

        @objc var friends: [Person] = []

        @objc var bestFriend: Person? = nil

        

        init(name: String) {

            self.name = name

        }

    }

    let gabrielle = Person(name: "Gabrielle")

    let jim = Person(name: "Jim")

    let yuanyuan = Person(name: "Yuanyuan")

    gabrielle.friends = [jim, yuanyuan]

    gabrielle.bestFriend = yuanyuan

    #keyPath(Person.name)

    // "name"

    gabrielle.value(forKey: #keyPath(Person.name))

    // "Gabrielle"

    #keyPath(Person.bestFriend.name)

    // "bestFriend.name"

    gabrielle.value(forKeyPath: #keyPath(Person.bestFriend.name))

    // "Yuanyuan"

    #keyPath(Person.friends.name)

    // "friends.name"

    gabrielle.value(forKeyPath: #keyPath(Person.friends.name))

    三、@objc dynamic应用于变量是为了让变量能够使用kvo机制。

    class MyObjectToObserve: NSObject {

        @objc dynamic var myDate = NSDate(timeIntervalSince1970: 0) // 1970

        func updateDate() {

            myDate = myDate.addingTimeInterval(Double(2 << 30)) // Adds about 68 years.

        }

    }

    class MyObserver: NSObject {

        @objc var objectToObserve: MyObjectToObserve

        var observation: NSKeyValueObservation?

        

        init(object: MyObjectToObserve) {

            objectToObserve = object

            super.init()

            

            observation = observe(

                .objectToObserve.myDate,

                options: [.old, .new]

            ) { object, change in

                print("myDate changed from: (change.oldValue!), updated to: (change.newValue!)")

            }

        }

    }

    let observed = MyObjectToObserve()

    let observer = MyObserver(object: observed)

    observed.updateDate() // Triggers the observer's change handler.

    // Prints "myDate changed from: 1970-01-01 00:00:00 +0000, updated to: 2038-01-19

    Here’s the least you need to remember:

    • @objc makes things visible to Objective-C code. You might need this for setting up target/action on buttons and gesture recognizers.
    • dynamic opts into dynamic dispatch. You might need this for KVO support or if you‘re doing method swizzling.
    • The only way to do dynamic dispatch currently is through the Objective-C runtime, so you must add @objc if you use dynamic.

    native-objc-dynamic.png

    https://www.cnblogs.com/feng9exe/p/9460336.html

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  • 原文地址:https://www.cnblogs.com/feng9exe/p/10472366.html
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