为什么我不能在这个应用程序中使用其他铅笔或颜色？它只能画黑色。这是我的代码：

import UIKit
import PencilKit
import PhotosUI
​
class ViewController: UIViewController, PKCanvasViewDelegate, PKToolPickerObserver {
​
    @IBOutlet weak var pencilButton: UIBarButtonItem!
    
    @IBOutlet weak var canvasView: PKCanvasView!
    
    let canvasWidth: CGFloat = 768
    let canvasOverScrollHeight: CGFloat = 500
    let drawing = PKDrawing()
​
    
    override func viewDidLoad() {
        super.viewDidLoad()
        canvasView.drawing = drawing
        canvasView.delegate = self
        canvasView.alwaysBounceVertical = true
        canvasView.drawingPolicy = .anyInput
        
        }
    
    
   override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
​
        let toolPicker = PKToolPicker()
        toolPicker.setVisible(true, forFirstResponder: canvasView)
        toolPicker.addObserver(canvasView)
        canvasView.becomeFirstResponder()
    }
   
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        
        let canvasScale = canvasView.bounds.width / canvasWidth
        canvasView.minimumZoomScale = canvasScale
        canvasView.maximumZoomScale = canvasScale
        canvasView.zoomScale = canvasScale
        
        updateContentSizeForDrawing()
        canvasView.contentOffset = CGPoint(x: 0, y: -canvasView.adjustedContentInset.top)
    }
    
    override var prefersHomeIndicatorAutoHidden: Bool{
        return true
    }
    
    @IBAction func fingerOrPencil (_ sender: Any) {
        canvasView.allowsFingerDrawing.toggle()
        pencilButton.title = canvasView.allowsFingerDrawing ? "Finger" : "Pencil"
    }
    
    
    @IBAction func saveToCameraRoll(_ sender: Any) {
        
        UIGraphicsBeginImageContextWithOptions(canvasView.bounds.size, false, UIScreen.main.scale)
        canvasView.drawHierarchy(in: canvasView.bounds, afterScreenUpdates: true)
        
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        if image != nil {
            PHPhotoLibrary.shared().performChanges({
                PHAssetChangeRequest.creationRequestForAsset(from: image!)
            }, completionHandler: {success, error in
            
            })
        }
    }
    
    
    
    func updateContentSizeForDrawing() {
        let drawing = canvasView.drawing
        let contentHeight: CGFloat
        
        if !drawing.bounds.isNull {
            contentHeight = max(canvasView.bounds.height, (drawing.bounds.maxY + self.canvasOverScrollHeight) * canvasView.zoomScale)
        } else {
            contentHeight = canvasView.bounds.height
        }
        canvasView.contentSize = CGSize(width: canvasWidth * canvasView.zoomScale, height: contentHeight)
    }
    
    // Delegate Methods
    
    func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
       updateContentSizeForDrawing()
      
    }
    func canvasViewDidEndUsingTool(_ canvasView: PKCanvasView) {
        
    }
    func canvasViewDidFinishRendering(_ canvasView: PKCanvasView) {
        
    }
    func canvasViewDidBeginUsingTool(_ canvasView: PKCanvasView) {
        
    }
}

以下是控制台中的输出：
2023 - 01 - 04 18：34：04.429420 + 0300绘图[45460：449613][Assert] UINavigationBar对于UINavigationController解码为解锁，或者navigationBar委托设置不正确。配置不一致可能会导致问题。navigationController =〈UINavigationController：0x123024000〉，导航栏=〈UI导航栏：0x12140a0a0;帧=（0 47; 0 50）;不透明=否;自动调整大小= W;图层=〈CALayer：0x6000030afae0〉〉委托= 0x123024000
2023 - 01 - 04 18：34：04.468831 + 0300图纸[45460：449613]金属API确认已启用
2023 - 01 - 04 18：34：04.705019 + 0300工程图[45460：449613][工具选择器]缺少默认字典，无法恢复以下项的状态：PK调色板命名默认值
2023 - 01 - 04 18：35：00.196200 + 0300图纸[45460：449613]键盘无法显示视图控制器（尝试显示〈UIColorPickerViewController：0x121846e00〉）