swiftui - 从 SwiftUI 环境中捕获 UndoManager

Question

我希望能够从我的文档模型中访问 UndoManager，这样我就可以在模型中注册撤消操作:

// Assume I've extended MyDocument to conform to ReferenceFileDocument elsewhere...
final class MyDocument {
    private var undoManager: UndoManager?

    @Published var aNumber = 5 {
        willSet {
            if let undoManager = undoManager {
                let currentValue = self.aNumber
                undoManager.registerUndo(withTarget: self) { target in
                    target.aNumber = currentValue
                }
            }
        }
    }

    func setUndoManager(undoManager: UndoManager?) {
        self.undoManager = undoManager
    }
}

要注册undoManager，我试过这个:

struct DocumentView: View {
    let document : MyDocument
    @Environment(\.undoManager) var undoManager
    
    var body: some View {
        MyDocumentEditor(document: document)
        .onAppear {
            document.setUndoManager(undoManager: undoManager)
        }
    }
}

当运行我的应用程序并加载保存的文档时，这有效。但是当从一个新文档开始时，UndoManager 为 nil。

我试过这样的事情:

@Environment(\.undoManager) var undoManager { 
    didSet { 
        self.document.setUndoManager(undoManager: undoManager)
    }
}

我的目标是尽量在模型和 View 中保留尽可能多的逻辑，并尽可能只关注 UI 内容。我希望 ReferenceFileDocument 提供一个属性来访问其关联的 UndoManager，就像 NSDocument 一样。

Answer 1

SwiftUI 使用下面的方法看起来更自然

var body: some View {
    TopLevelView(document: document, undoManager: undoManager)
}

和

struct TopLevelView: View {
    @ObservedObject var document : MyDocument
    var undoManager: UndoManager?

    init(document: MyDocument, undoManager: UndoManager?) {
       self.document = document
       self.undoManager = undoManager

       self.setUndoManager(undoManager: undoManager)
    }

    // ... other code
}