如何在 SwiftUI 中视图消失时关闭 PKToolPicker？

Question

我正在尝试将 PKCanvasView 包装为名为 CanvasView 的 SwiftUI 视图。我希望能够在另一个视图之上切换整个 canvas。当 CanvasView 出现时，我希望 PKToolPicker 出现。当它消失时，我希望 PKToolPicker 消失。

我在这里找到了一些类似的方法，但它们只涉及显示选择器或使用按钮切换选择器；我希望选择器可见性与视图可见性相关联。

在下面的示例中，您可以看到可以切换 canvas，但是一旦工具选择器可见，它就会保持可见。

这是我的 CanvasView:

import SwiftUI
import PencilKit

struct CanvasView: UIViewRepresentable {

    class Coordinator: NSObject, PKCanvasViewDelegate {
        var canvasView: Binding<PKCanvasView>
        let onChange: () -> Void

        init(canvasView: Binding<PKCanvasView>, onChange: @escaping () -> Void) {
            self.canvasView = canvasView
            self.onChange = onChange
        }

        func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
            if canvasView.drawing.bounds.isEmpty == false {
                onChange()
            }
        }
    }

    @Binding var canvasView: PKCanvasView
    @Binding var toolPickerIsActive: Bool
    private let toolPicker = PKToolPicker()

    let onChange: () -> Void

    func makeUIView(context: Context) -> PKCanvasView {
        canvasView.backgroundColor = .clear
        canvasView.isOpaque = true
        canvasView.delegate = context.coordinator
        showToolPicker()

        return canvasView
    }

    func updateUIView(_ uiView: PKCanvasView, context: Context) {
        toolPicker.setVisible(toolPickerIsActive, forFirstResponder: uiView)
    }

    func showToolPicker() {
      toolPicker.setVisible(true, forFirstResponder: canvasView)
      toolPicker.addObserver(canvasView)
      canvasView.becomeFirstResponder()
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(canvasView: $canvasView, onChange: onChange)
    }
}

还有一个例子ContentView:

struct ContentView: View {
    @State private var canvasView = PKCanvasView()
    @State private var toolPickerIsActive = false
    @State private var canvasIsVisible = false

    var body: some View {
        ZStack {
            if canvasIsVisible {
                CanvasView(canvasView: $canvasView,
                           toolPickerIsActive: $toolPickerIsActive,
                           onChange: canvasDidChange)
                    .onAppear { toolPickerIsActive = true }
                    .onDisappear { toolPickerIsActive = false }
            }

            Button(action: {
                canvasIsVisible.toggle()
            }, label: {
                Text("Toggle canvas view")
            })
        }
    }

    private func canvasDidChange() {
        // Do something with updated canvas.
    }
}

任何指导将不胜感激！

Answer 1

在您的场景中，CanvasView 在消失时被销毁，因此 SwiftUI 渲染引擎不会在任何状态更改时更新它（因为它认为没有必要这样做）。

此用例的可能解决方案是在协调器上隐藏选择器deinit（因为它已被所有者视图销毁）。

这是一个演示。使用 Xcode 12.4 / iOS 14.4

测试

struct CanvasView: UIViewRepresentable {

    class Coordinator: NSObject, PKCanvasViewDelegate {
        var canvasView: Binding<PKCanvasView>
        let onChange: () -> Void
        private let toolPicker: PKToolPicker

        deinit {       // << here !!
            toolPicker.setVisible(false, forFirstResponder: canvasView.wrappedValue)
            toolPicker.removeObserver(canvasView.wrappedValue)
        }

        init(canvasView: Binding<PKCanvasView>, toolPicker: PKToolPicker, onChange: @escaping () -> Void) {
            self.canvasView = canvasView
            self.onChange = onChange
            self.toolPicker = toolPicker
        }

        func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
            if canvasView.drawing.bounds.isEmpty == false {
                onChange()
            }
        }
    }

    @Binding var canvasView: PKCanvasView
    @Binding var toolPickerIsActive: Bool
    private let toolPicker = PKToolPicker()

    let onChange: () -> Void

    func makeUIView(context: Context) -> PKCanvasView {
        canvasView.backgroundColor = .clear
        canvasView.isOpaque = true
        canvasView.delegate = context.coordinator
        showToolPicker()

        return canvasView
    }

    func updateUIView(_ uiView: PKCanvasView, context: Context) {
        toolPicker.setVisible(toolPickerIsActive, forFirstResponder: uiView)
    }

    func showToolPicker() {
        toolPicker.setVisible(true, forFirstResponder: canvasView)
        toolPicker.addObserver(canvasView)
        canvasView.becomeFirstResponder()
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(canvasView: $canvasView, toolPicker: toolPicker, onChange: onChange)
    }
}

struct ContentView: View {
    @State private var canvasView = PKCanvasView()
    @State private var toolPickerIsActive = false
    @State private var canvasIsVisible = false

    var body: some View {
        ZStack {
            if canvasIsVisible {
                CanvasView(canvasView: $canvasView,
                              toolPickerIsActive: $toolPickerIsActive,
                              onChange: canvasDidChange)
                    .onAppear { toolPickerIsActive = true }
//                    .onDisappear { toolPickerIsActive = false }
            }

            Button(action: {
                canvasIsVisible.toggle()
            }, label: {
                Text("Toggle canvas view")
            })
        }
    }

    private func canvasDidChange() {
        // Do something with updated canvas.
    }
}

注意：可能会重新设计所有权，因此 toolPicker 将仅存在于协调器中，但它不会改变想法，由您决定。

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