如何使UILabel在图像未被跟踪时出现在屏幕上，并在图像被跟踪时消失

import ARKit

class ViewController: UIViewController, ARSCNViewDelegate {
    @IBOutlet weak var sceneView: ARSCNView!
    @IBOutlet weak var label: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        sceneView.delegate = self
        
        // 创建一个平面检测配置
        let configuration = ARWorldTrackingConfiguration()
        configuration.planeDetection = .horizontal
        
        // 运行AR会话
        sceneView.session.run(configuration)
        
        // 隐藏UILabel
        label.isHidden = true
    }
    
    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
        // 当检测到平面时，显示UILabel
        if anchor is ARPlaneAnchor {
            DispatchQueue.main.async {
                self.label.isHidden = false
            }
        }
    }
    
    func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {
        // 当平面更新时，保持UILabel的显示状态
        if anchor is ARPlaneAnchor && !label.isHidden {
            DispatchQueue.main.async {
                self.label.isHidden = false
            }
        }
    }
    
    func renderer(_ renderer: SCNSceneRenderer, didRemove node: SCNNode, for anchor: ARAnchor) {
        // 当平面移除时，隐藏UILabel
        if anchor is ARPlaneAnchor {
            DispatchQueue.main.async {
                self.label.isHidden = true
            }
        }
    }
}