SwiftUI macOS 命令（菜单栏）和视图

Question

嗨，我开始学习 SwiftUI 和 macOS 开发。我正在使用 SwiftUI 生命周期。如何从菜单栏的焦点 window 中调用函数。

除了 Apple 文档，我发现 this reference 并且能够使用命令创建菜单项，但我不知道如何从我的视图中调用函数。

例如：

假设这是我的 App 结构：

import SwiftUI

@main
struct ExampleApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }.commands {
        CommandMenu("First menu") {
            Button("Action!") {
                // How do I call the views action function?
            }
        }
    }
}

这是我的观点：

struct ContentView: View {
    public func action() {
        print("It works")
    }
    var body: some View {
        Text("Example")
    }
}

我刚刚输入了示例代码，抱歉，如果有任何错别字，但我希望你能理解。

Answer 1

因为 SwiftUI 中的 Views 是瞬态的，你不能持有对 ContentView 的特定实例的引用来调用它的函数。但是，您可以做的是更改传递给内容视图的部分状态。

例如：

@main
struct ExampleApp: App {
    @StateObject var appState = AppState()
    
    var body: some Scene {
        WindowGroup {
            ContentView(appState: appState)
                .frame(maxWidth: .infinity, maxHeight: .infinity)
        }.commands {
            CommandMenu("First menu") {
                Button("Action!") {
                    appState.textToDisplay = "\(Date())"
                }
            }
        }
    }
}

class AppState : ObservableObject {
    @Published var textToDisplay = "(not clicked yet)"
}

struct ContentView: View {
    @ObservedObject var appState : AppState
    
    var body: some View {
        Text(appState.textToDisplay)
    }
}

注意.commands修饰符继续WindowGroup { }

在此示例中，AppState 是一个 ObservableObject，它保存应用程序的某些状态。它使用参数传递给 ContentView。您也可以通过环境对象 (https://www.hackingwithswift.com/quick-start/swiftui/how-to-use-environmentobject-to-share-data-between-views)

传递它

单击菜单项时，它会设置 textToDisplay，即 AppState 上的 @Published 属性。 ContentView 将在更新 AppState 的 @Published 属性时更新。

这是您要使用的模式的总体思路。如果您有此模式未涵盖的用例，请在评论中告诉我。

根据您的评论进行更新：

import SwiftUI
import Combine

@main
struct ExampleApp: App {
    @StateObject var appState = AppState()
    
    var body: some Scene {
        WindowGroup {
            ContentView(appState: appState)
                .frame(maxWidth: .infinity, maxHeight: .infinity)
        }.commands {
            CommandMenu("First menu") {
                Button("Action!") {
                    appState.textToDisplay = "\(Date())"
                }
                Button("Change background color") {
                    appState.contentBackgroundColor = Color.green
                }
                Button("Toggle view") {
                    appState.viewShown.toggle()
                }
                Button("CustomCopy") {
                    appState.customCopy.send()
                }
            }
        }
    }
}

class AppState : ObservableObject {
    @Published var textToDisplay = "(not clicked yet)"
    @Published var contentBackgroundColor = Color.clear
    @Published var viewShown = true
    
    var customCopy = PassthroughSubject<Void,Never>()
}

class ViewModel : ObservableObject {
    @Published var text = "The text I have here"
    var cancellable : AnyCancellable?

    func connect(withAppState appState: AppState) {
        cancellable = appState.customCopy.sink(receiveValue: { _ in
            print("Do custom copy based on my state: \(self.text) or call a function")
        })
    }
}

struct ContentView: View {
    @ObservedObject var appState : AppState
    @State var text = "The text I have here"
    @StateObject private var viewModel = ViewModel()
    
    var body: some View {
        VStack {
            Text(appState.textToDisplay)
                .background(appState.contentBackgroundColor)
            if appState.viewShown {
                Text("Shown?")
            }
        }
        .onReceive(appState.$textToDisplay) { (newText) in
            print("Got new text: \(newText)")
        }
        .onAppear {
            viewModel.connect(withAppState: appState)
        }
    }
}

在我的更新中，您可以看到我已经解决了背景颜色的问题，显示隐藏视图，甚至在其中一个 @Published 属性更改时收到通知（通过 onReceive） .

您还可以看到我如何使用自定义发布者 (customCopy) 将操作传递给 ContentView 的 ViewModel

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