SwiftUI中Sheet内PKCanvasView触发关闭时工具消失的问题

场景代码 #

调用Sheet展示绘图视图的代码：

...
.sheet { DrawingView() }

承载PKCanvasView的DrawingView实现：

struct DrawingView: View {
    private var canvasView = PKCanvasView()
    @Environment(\.dismiss) var dismiss

    var body: some View {
        NavigationStack {
            GeometryReader { proxy in
                MyCanvas(canvasView: canvasView)
            }
...
}

PKCanvasView的UIViewRepresentable包装实现：

struct MyCanvas: UIViewRepresentable {
    var canvasView: PKCanvasView
    @Binding var oldImage: UIImage?
    let picker = PKToolPicker()

    func makeUIView(context: Context) -> PKCanvasView {
        self.canvasView.tool = PKInkingTool(.pen, color: .black, width: 15)
        self.canvasView.becomeFirstResponder()
        return canvasView
    }
    
    func updateUIView(_ uiView: PKCanvasView, context: Context) {
        print(#function, uiView.drawing.strokes.count)
        picker.addObserver(canvasView)
        picker.setVisible(true, forFirstResponder: uiView)
        DispatchQueue.main.async {
            uiView.becomeFirstResponder()
        }
    }
}

问题现象与推测 #

当前基础功能正常，但存在以下异常：

• 触发sheet滑动关闭操作时，PKCanvasView的工具条会自动消失
• 重新上滑打开sheet后，工具条依旧不可见，仅能使用最后一次选中的画笔进行绘画

推测核心原因是第一响应者丢失：SwiftUI在sheet滑动关闭过程中，会让PKCanvasView失去第一响应者身份，进而导致工具条被隐藏，逻辑类似sheet滑动关闭时键盘自动隐藏的行为。

内容的提问来源于stack exchange，提问作者thisIsTheFoxe