SwiftUI距离传感器报错：Found no UIEvent for backing event of type:14 求助

测试距离传感器（Proximity Sensor）时，每次触发传感器，错误日志都会反复出现以下信息：

2023-10-03 02:37:36.095925+0900 PushUp[40969:7329614] [EventDispatcher] Found no UIEvent for backing event of type: 14; contextId: 0x0

对应的SwiftUI实现代码如下：

import SwiftUI

struct ProximitySensor: View {
    @State private var theNumber = 30
    
    let TTS = TextToSpeech()
    let device = UIDevice.current
    
    init() {
        device.isProximityMonitoringEnabled = true
    }
    
    var body: some View {
        VStack {
            Text("\(theNumber)")
                .id("theNumber" + "\(theNumber)")
                .font(.system(size: 100))
                .fontWeight(.heavy)
                .italic()
        }.onReceive(NotificationCenter.default.publisher(
            for: UIDevice.proximityStateDidChangeNotification), perform: { _ in
                if UIDevice.current.proximityState {
                    theNumber += 1
                    let toHan = getOrdinaryNumber(theNumber)
                    TTS.speak(text: toHan)
                }
            }
        )
        
    }
}

错误修复 #

这条日志属于系统级警告，并非代码逻辑错误，但可通过调整操作时机消除：

• 问题本质：距离传感器状态变化通知触发时，SwiftUI视图更新与系统事件调度存在短暂时序差，导致系统找不到对应UIEvent。
• 修复代码：在处理通知时延迟执行业务逻辑，给系统留出事件调度时间：

.onReceive(NotificationCenter.default.publisher(for: UIDevice.proximityStateDidChangeNotification)) { _ in
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.05) {
        if UIDevice.current.proximityState {
            theNumber += 1
            let toHan = getOrdinaryNumber(theNumber)
            TTS.speak(text: toHan)
        }
    }
}

更优实现方式 #

1. 封装传感器管理逻辑 #

将传感器的启用、状态监听封装到独立的ObservableObject中，分离视图与业务逻辑：

class ProximityManager: ObservableObject {
    @Published var proximityState = false
    private let device = UIDevice.current
    
    init() {
        device.isProximityMonitoringEnabled = true
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(updateProximityState),
            name: UIDevice.proximityStateDidChangeNotification,
            object: nil
        )
    }
    
    @objc private func updateProximityState() {
        proximityState = device.proximityState
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

2. 简化视图层实现 #

使用@StateObject订阅传感器状态，代码更简洁易维护：

struct ProximitySensor: View {
    @State private var theNumber = 30
    @StateObject private var proximityManager = ProximityManager()
    let TTS = TextToSpeech()
    
    var body: some View {
        VStack {
            Text("\(theNumber)")
                .font(.system(size: 100, weight: .heavy))
                .italic()
        }
        .onChange(of: proximityManager.proximityState) { newState in
            if newState {
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.05) {
                    theNumber += 1
                    let toHan = getOrdinaryNumber(theNumber)
                    TTS.speak(text: toHan)
                }
            }
        }
    }
}

3. 其他细节优化 #

• 移除不必要的.id("theNumber" + "\(theNumber)")：SwiftUI会自动根据@State变量变化更新视图，手动设置id易引发不必要的视图重建。
• 合并字体设置：将.font(.system(size: 100))与.fontWeight(.heavy)合并为.font(.system(size: 100, weight: .heavy))，简化代码。

内容的提问来源于stack exchange，提问作者goodman