SwiftUI中使用Combine的資料流

你好???? 我花了 10 多個小時來實作Combine框架，但不清楚如何鏈接Publisher和Subscriber. 在示例中，我只想setTheme從類中呼叫 funkTheme并自動更新類game中的變數Game。我知道如何實作它，didSet但主要目標是用Combine. 非常感謝您的幫助。

import SwiftUI
import Combine
import Foundation

class Theme: ObservableObject {
    
    @Published private(set) var choosenTheme: Color? // Publisher right?
    
    func setTheme(with color: Color?) {
        if let unwrappedColor = color {
            self.choosenTheme = unwrappedColor
        } else {
            self.choosenTheme = nil
        }
    }
}

class Game: ObservableObject {
    
    @Published var game: String? // Subscriber right?
    private let gameTheme = Theme()
    private var cancellables = Set<AnyCancellable>()
    
    init() {
        addSubscribers()
    }
    
    private func addSubscribers() { // I think something wrong here
        gameTheme.$choosenTheme
            .map(createGame)
            .sink { [weak self] (returnedString) in
                print("Value from sink \(String(describing: returnedString))")
                self?.game = returnedString
            }
            .store(in: &cancellables)
    }
    
    private func createGame(for theme: Color?) -> String? {
       if let unwrappedTheme = theme {
           print(unwrappedTheme)
           return String("\(unwrappedTheme)")
       } else {
           return nil
       }
   }
}

// Test:
var testTheme = Theme()
testTheme.setTheme(with: .orange)

var testGame = Game()
print(testGame.game) // Should be Orange

testTheme.setTheme(with: .blue)
print(testGame.game) // Should be Blue

testTheme.setTheme(with: nil)
print(testGame.game) // Should be nil

uj5u.com熱心網友回復：

您遇到的問題是有兩個實體Theme

您在此處創建的一個：

// Test:
var testTheme = Theme()

還有一個在里面Game：

private let gameTheme = Theme()

然后你正在改變第一個主題并期望第二個主題改變。要解決問題，您必須Theme將Game.

首先，您需要進行一些更改以Game允許Theme注入：

class Game: ObservableObject {
    
    @Published var game: String?
    private let gameTheme: Theme
    private var cancellables = Set<AnyCancellable>()
    
    init(gameTheme: Theme) {
        self.gameTheme = gameTheme
        addSubscribers()
    }

接下來，您必須在測驗時執行該注入：

var testTheme = Theme()
testTheme.setTheme(with: .orange)

var testGame = Game(gameTheme: testTheme)

如果您這樣做 - 您將看到更改正確反映在列印件中。

如果您愿意，可以顯著簡化您的兩個類：

class Theme: ObservableObject {
    
    @Published private(set) var chosenTheme: Color?
    
    func setTheme(with color: Color?) {
        chosenTheme = color
    }
}

class Game: ObservableObject {
    
    @Published var game: String?
    private let gameTheme: Theme
    
    init(gameTheme: Theme) {
        self.gameTheme = gameTheme
        addBindings()
    }
    
    private func addBindings() {
        gameTheme
            .$chosenTheme
            .map(createGame)
            .assign(to: &$game)
    }
    
    private func createGame(for theme: Color?) -> String? {
        theme.map { $0.description }
   }
}

uj5u.com熱心網友回復：

它根本不應該改變。你正在做的是設定一個實體的主題Theme。但是，在您的Game課堂上，您正在聽另一堂課。

你現在看到問題了嗎？Game要么用你正在更新的主題初始化你，要么制作Theme一個singleton.

嘗試這個：

import SwiftUI
import Combine
import Foundation

class Theme: ObservableObject {
    static var shared = Theme()
    @Published private(set) var choosenTheme: Color? // Publisher right?
    
    func setTheme(with color: Color?) {
        if let unwrappedColor = color {
            self.choosenTheme = unwrappedColor
        } else {
            self.choosenTheme = nil
        }
    }
}

class Game: ObservableObject {
    
    @Published var game: String? // Subscriber right?
    private let gameTheme = Theme.shared
    private var cancellables = Set<AnyCancellable>()
    
    init() {
        addSubscribers()
    }
    
    private func addSubscribers() { // I think something wrong here
        gameTheme.$choosenTheme
            .map(createGame)
            .sink { [weak self] (returnedString) in
                print("Value from sink \(String(describing: returnedString))")
                self?.game = returnedString
            }
            .store(in: &cancellables)
    }
    
    private func createGame(for theme: Color?) -> String? {
       if let unwrappedTheme = theme {
           print(unwrappedTheme)
           return String("\(unwrappedTheme)")
       } else {
           return nil
       }
   }
}

// Test:

var testGame = Game() //Game initialization should precede Theme because now the listener starts listening for the orange change 

var testTheme = Theme.shared
testTheme.setTheme(with: .orange)

print(testGame.game) // Should be Orange

testTheme.setTheme(with: .blue)
print(testGame.game) // Should be Blue

testTheme.setTheme(with: nil)
print(testGame.game) // Should be nil

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