@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, width: 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.

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