编辑:感谢一些反馈,我已经能够部分工作(更新代码以反射(reflect)当前更改)。
即使该应用程序似乎按预期运行,我仍然收到“正在修改状态...”警告。如何在 updateUIView
中更新 View 的绘图并使用 canvasViewDrawingDidChange
将新绘图推送到堆栈上而不导致此问题?我曾尝试将其包装在调度调用中,但这只会造成无限循环。
我正在尝试在 UIViewRepresentable
(PKCanvasView
) 中实现撤消功能。我有一个名为 WriterView
的父 SwiftUI View ,它包含两个按钮和 Canvas 。
这是父 View :
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)
}
}
}
我收到以下错误:
[SwiftUI] Modifying state during view update, this will cause undefined behavior.
大概是我的协调员的 did change 函数引起的,但我不确定如何解决这个问题。解决这个问题的最佳方法是什么?
谢谢!
最佳答案
我终于(无意中)弄清楚了如何使用 UndoManager 来做到这一点。我仍然不确定 为什么 这行得通,因为我从来不需要调用 self.undoManager?.registerUndo()
。如果您理解为什么我从来不需要注册事件,请发表评论。
这是我的工作父 View :
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)
}
}
}
这是我工作的 subview :
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) { }
}
这当然感觉更像是 SwiftUI 的预期方法,并且肯定比我之前所做的尝试更优雅。
https://stackoverflow.com/questions/60592875/