使用PencilKit实现SwiftUI撤消功能

Question

编辑:感谢一些反馈，我已经能够让这个部分工作(更新的代码来反映当前的变化)。

尽管该应用程序看起来像预期的那样工作，但我仍然得到“修改状态.”。警告。如何更新视图在updateUIView中的绘图，并在不引起此问题的情况下使用canvasViewDrawingDidChange将新的绘图推送到堆栈中？我尝试过将其封装在调度调用中，但这只是创建了一个无限循环。

我试图在UIViewRepresentable (PKCanvasView)中实现撤销功能。我有一个名为SwiftUI的父视图WriterView，它包含两个按钮和画布。

，这是父视图：

struct WriterView: View {
    @State var drawings: [PKDrawing] = [PKDrawing()]

    var body: some View {
        VStack(spacing: 10) {
            Button("Clear") {
                self.drawings = []
            }
            Button("Undo") {
                if !self.drawings.isEmpty {
                    self.drawings.removeLast()
                }
            }
            MyCanvas(drawings: $drawings)
        }
    }
}

下面是我如何实现我的UIViewRepresentable**:**

struct MyCanvas: UIViewRepresentable {
    @Binding var drawings: [PKDrawing]

    func makeUIView(context: Context) -> PKCanvasView {
        let canvas = PKCanvasView()
        canvas.delegate = context.coordinator
        return canvas
    }

    func updateUIView(_ uiView: PKCanvasView, context: Context) {
        uiView.drawing = self.drawings.last ?? PKDrawing()
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(self._drawings)
    }

    class Coordinator: NSObject, PKCanvasViewDelegate {
        @Binding drawings: [PKDrawing]

        init(_ drawings: Binding<[PKDrawing]>) {
            self._drawings = drawings
        }

        func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
            drawings.append(canvasView.drawing)
        }
    }
}

我得到了以下错误：

在视图更新期间，

SwiftUI修改状态，这将导致未定义的行为。

据推测，这是由我的协调器的更改函数引起的，但我不知道如何解决这个问题。解决这个问题的最好方法是什么？

谢谢!

Answer 1

我终于(意外地)想出了如何使用UndoManager来完成这个任务。我仍然不清楚为什么会这样，因为我从来不需要打电话给self.undoManager?.registerUndo()。如果你明白我为什么不需要注册一个事件，请发表评论。

这里是我的工作父视图：

struct Writer: View {
    @Environment(\.undoManager) private var undoManager
    @State private var canvasView = PKCanvasView()
    
    var body: some View {
        VStack(spacing: 10) {
            Button("Clear") {
                canvasView.drawing = PKDrawing()
            }
            Button("Undo") {
                undoManager?.undo()
            }
            Button("Redo") {
                undoManager?.redo()
            }
            MyCanvas(canvasView: $canvasView)
        }
    }
}

，这是我的工作子视图：

struct MyCanvas: UIViewRepresentable {
    @Binding var canvasView: PKCanvasView
    
    func makeUIView(context: Context) -> PKCanvasView {
        canvasView.drawingPolicy = .anyInput
        canvasView.tool = PKInkingTool(.pen, color: .black, width: 15)
        return canvasView
    }

    func updateUIView(_ canvasView: PKCanvasView, context: Context) { }
}

这当然更像是SwiftUI的预期方法，而且肯定比我之前所做的尝试更优雅。

Answer 2

为了完整起见，如果您想显示PKToolPicker，这里是我的UIViewRepresentable。

import Foundation
import SwiftUI
import PencilKit

struct PKCanvasSwiftUIView : UIViewRepresentable {

let canvasView = PKCanvasView()

#if !targetEnvironment(macCatalyst)
let coordinator = Coordinator()

class Coordinator: NSObject, PKToolPickerObserver {
    // initial values 
    var color = UIColor.black
    var thickness = CGFloat(30)

    func toolPickerSelectedToolDidChange(_ toolPicker: PKToolPicker) {
        if toolPicker.selectedTool is PKInkingTool {
            let tool = toolPicker.selectedTool as! PKInkingTool
            self.color = tool.color
            self.thickness = tool.width
        }
    }
    func toolPickerVisibilityDidChange(_ toolPicker: PKToolPicker) {
        if toolPicker.selectedTool is PKInkingTool {
            let tool = toolPicker.selectedTool as! PKInkingTool
            self.color = tool.color
            self.thickness = tool.width
        }
    }
}
func makeCoordinator() -> PKCanvasSwiftUIView.Coordinator {
    return Coordinator()
}
#endif

func makeUIView(context: Context) -> PKCanvasView {
    canvasView.isOpaque = false
    canvasView.backgroundColor = UIColor.clear
    canvasView.becomeFirstResponder()
    #if !targetEnvironment(macCatalyst)
    if let window = UIApplication.shared.windows.filter({$0.isKeyWindow}).first,
        let toolPicker = PKToolPicker.shared(for: window) {
        toolPicker.addObserver(canvasView)
        toolPicker.addObserver(coordinator)
        toolPicker.setVisible(true, forFirstResponder: canvasView)
    }
    #endif
    return canvasView
}

func updateUIView(_ uiView: PKCanvasView, context: Context) {

}
} 

Answer 3

我认为错误可能来自私有func clearCanvas()和私有func undoDrawing()。试一试，看看它是否有效：

private func clearCanvas() {
 DispatchQueue.main.async {
    self.drawings = [PKDrawing()]
 }
}

undoDrawing()也是如此。

如果它来自canvasViewDrawingDidChange，那么做同样的技巧。