@Published属性与绑定

注意：Combine可以在SwiftUI和UIKit下工作，本例中在Playground中使用的是UIKit

示例一：将演示在ViewModel使用@Published属性并将它绑定到视图控件

import Foundation
import UIKit
import Combine

final class FormViewModel {
    @Published var isSubmitAllowed: Bool = true
}

final class FormViewController: UIViewController {

    var viewModel = FormViewModel()
    let submitButton = UIButton()

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // subscribe to a @Published property using the $ wrapped accessor
        viewModel.$isSubmitAllowed
            .receive(on: DispatchQueue.main)
            .print()
            .assign(to: \.isEnabled, on: submitButton)
    }
}

print("Demonstrating @Published")

let formViewController = FormViewController(nibName: nil, bundle: nil)
print("Button enabled is \(formViewController.submitButton.isEnabled)")
formViewController.viewModel.isSubmitAllowed = false
print("Button enabled is \(formViewController.submitButton.isEnabled)")

输出：

Demonstrating @Published
Button enabled is true
Button enabled is true

示例二：将演示使用ObservableObject，生成多个@Published并订阅其值的变化

print("Demonstrating ObservableObject")

class ObservableFormViewModel: ObservableObject {
    @Published var isSubmitAllowed: Bool = true
    @Published var username: String = ""
    @Published var password: String = ""
    var somethingElse: Int = 10
}

var form = ObservableFormViewModel()

let formSubscription = form.objectWillChange.sink { _ in
    print("Form changed: \(form.isSubmitAllowed) \"\(form.username)\" \"\(form.password)\"")
}

form.isSubmitAllowed = false
form.username = "Florent"
form.password = "12345"
form.somethingElse = 0

注意：objectWillChange是值即将改变的消息，somethingElse属性没有设置@Published其不会有输出

输出:

Demonstrating ObservableObject
Form changed: true "" ""
Form changed: false "" ""
Form changed: false "Florent" ""

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