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ios - SwiftUI 中的 PencilKit

问题描述

我正在尝试PencilKit在 SwiftUI 中使用。

  1. 如何在updateUIView-function 中检测到哪个Binding-variable 已更新？例如，我不想在更改颜色时清除画布。
  2. 还有比切换布尔值更好的方法来清除画布吗？切换布尔值会强制updateUIView执行 -function。
import SwiftUI
import UIKit
import PencilKit

struct ContentView: View {
    @State var color = UIColor.black
    @State var clear = false

    var body: some View {
        VStack{
            PKCanvas(color: $color, clear:$clear)
            VStack(){
                Button("Change to BLUE"){ self.color = UIColor.blue }
                Button("Change to GREEN"){ self.color = UIColor.green }
                Button("Clear Canvas"){ self.clear.toggle() }
            }
        }
    }
}

struct PKCanvas: UIViewRepresentable {
    class Coordinator: NSObject, PKCanvasViewDelegate {
        var pkCanvas: PKCanvas

        init(_ pkCanvas: PKCanvas) {
            self.pkCanvas = pkCanvas
        }
    }

    @Binding var color:UIColor
    @Binding var clear:Bool

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

    func makeUIView(context: Context) -> PKCanvasView {
        let canvas = PKCanvasView()
        canvas.tool = PKInkingTool(.pen, color: color, width: 10)

        canvas.delegate = context.coordinator
        return canvas
    }

    func updateUIView(_ canvasView: PKCanvasView, context: Context) {
        // clears the canvas
        canvasView.drawing = PKDrawing()

        // sets a new color
        canvasView.tool = PKInkingTool(.pen, color: color, width: 10)
    }
}

标签： iosswiftswiftuiuiviewrepresentablepencilkit

解决方案

这可以解决问题：

    func updateUIView(_ canvasView: PKCanvasView, context: Context) {
        if clear != context.coordinator.pkCanvas.clear{
            canvasView.drawing = PKDrawing()
        }
        canvasView.tool = PKInkingTool(.pen, color: color, width: 10)
    }

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