SwiftUI中UITextViewRepresentable模拟器NaN警告问题求助

问题描述 #

在SwiftUI应用中使用UITextViewRepresentable时，鼠标悬停文本区域时模拟器会弹出以下警告：

Error: this application, or a library it uses, has passed an invalid numeric value (NaN, or not-a-number) to CoreGraphics API and this value is being ignored. Please fix this problem.

If you want to see the backtrace, please set CG_NUMERICS_SHOW_BACKTRACE

该问题仅在模拟器中出现，真机上无法复现。开启CG_NUMERICS_SHOW_BACKTRACE后得到调用栈：

2023-06-04 10:21:38.983039+0100 TextViewRepresentable[12699:10411840] [Unknown process name] Error: this application, or a library it uses, has passed an invalid numeric value (NaN, or not-a-number) to CoreGraphics API and this value is being ignored. Please fix this problem.
2023-06-04 10:21:38.992493+0100 TextViewRepresentable[12699:10411840] [Unknown process name] Backtrace:
  <CGPathMoveToPoint+71>
   <+[UIBezierPath _continuousRoundedRectBezierPath:withRoundedCorners:cornerRadii:segments:smoothPillShapes:]+1636>
    <+[UIBezierPath _continuousRoundedRectBezierPath:withRoundedCorners:cornerRadius:segments:]+170>
     <+[UIBezierPath _roundedRectBezierPath:withRoundedCorners:cornerRadius:segments:legacyCorners:]+337>
      <-[UIScrollViewAccessibility accessibilityPath]+1575>
       <-[NSObject(AXPrivCategory) _accessibilityBaseHitTest:withEvent:]+2879>
        <-[NSObject(AXPrivCategory) _accessibilityHitTest:withEvent:]+92>
         <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+154>
          <-[UIViewAccessibility __accessibilityHitTest:withEvent:]+1675>
           <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+101>
            <__64-[NSObject(AXPrivCategory) _accessibilityBaseHitTest:withEvent:]_block_invoke.243+180>
             <-[NSObject(AXPrivCategory) _accessibilityBaseHitTest:withEvent:]+4038>
              <-[NSObject(AXPrivCategory) _accessibilityHitTest:withEvent:]+92>
               <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+154>
                <-[UIViewAccessibility __accessibilityHitTest:withEvent:]+1675>
                 <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+101>
                  <-[UIViewAccessibility __accessibilityHitTest:withEvent:]+1675>
                   <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+101>
                    <-[UIViewAccessibility __accessibilityHitTest:withEvent:]+1675>
                     <-[UIViewAccessibility _accessibilityHitTest:withEvent:]+101>
                      <-[UIWindowAccessibility _accessibilityHitTest:withEvent:]+138>
                       <_copyElementAtPositionCallback+5184>
                        <___AXXMIGCopyElementAtPosition_block_invoke+79>
                         <_handleNonMainThreadCallback+424>
                          <_AXXMIGCopyElementAtPosition+670>
                           <_XCopyElementAtPosition+521>
                            <mshMIGPerform+1024>
                             <__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__+41>
                              <__CFRunLoopDoSource1+538>
                               <__CFRunLoopRun+2671>
                                <CFRunLoopRunSpecific+560>
                                 <GSEventRunModal+139>
                                  <-[UIApplication _run]+994>
                                   <UIApplicationMain+123>
                                    <__swift_memcpy93_8+12403>
                                     <__swift_memcpy93_8+12076>
                                      <__swift_memcpy195_8+14237>
                                       <$s21TextViewRepresentable0abC3AppV5$mainyyFZ+30>
                                        <main+9>
                                         107c8d384    

严重性分析 #

• 从调用栈看，问题出在辅助功能（Accessibility）相关的CoreGraphics路径绘制流程中，模拟器触发了NaN值传入，但CoreGraphics已主动忽略该无效值，不会导致应用崩溃。
• 仅在模拟器中出现、真机无复现，说明这大概率是模拟器的兼容性bug，不会影响线上用户的使用体验。
• 虽然当前不影响功能，但如果后续iOS版本更新或模拟器环境变化，不排除问题扩大的可能，建议尽量修复。

解决方法 #

1. 检查UITextViewRepresentable中的布局参数 #

确保配置UITextView时，所有和圆角、尺寸相关的参数没有计算出NaN值：

• 排查是否存在除以0的计算逻辑，比如动态计算圆角半径时的除数是否可能为0。
• 确保contentInset、cornerRadius等属性的赋值都是有效的非NaN数值。

示例代码（避免NaN）：

func makeUIView(context: Context) -> UITextView {
    let textView = UITextView()
    // 用max兜底避免动态值出现0或负数，确保圆角半径有效
    textView.layer.cornerRadius = max(8, dynamicCornerValue)
    textView.contentInset = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
    return textView
}

2. 重写UIScrollView的accessibilityPath #

调用栈指向UIScrollViewAccessibility的accessibilityPath方法，可自定义UITextView子类，重写该方法过滤NaN点：

class FixedAccessibilityTextView: UITextView {
    override var accessibilityPath: UIBezierPath? {
        guard let superPath = super.accessibilityPath else { return nil }
        let cleanedPath = UIBezierPath()
        
        superPath.forEach { element in
            switch element.type {
            case .moveToPoint:
                let point = element.points[0]
                if !point.x.isNaN && !point.y.isNaN {
                    cleanedPath.move(to: point)
                }
            case .addLineToPoint:
                let point = element.points[0]
                if !point.x.isNaN && !point.y.isNaN {
                    cleanedPath.addLine(to: point)
                }
            case .addCurveToPoint:
                let cp1 = element.points[0]
                let cp2 = element.points[1]
                let end = element.points[2]
                if !cp1.x.isNaN && !cp1.y.isNaN && !cp2.x.isNaN && !cp2.y.isNaN && !end.x.isNaN && !end.y.isNaN {
                    cleanedPath.addCurve(to: end, controlPoint1: cp1, controlPoint2: cp2)
                }
            default:
                cleanedPath.append(element)
            }
        }
        
        return cleanedPath.isEmpty ? superPath : cleanedPath
    }
}

之后在UITextViewRepresentable中使用该子类：

struct TextViewRepresentable: UIViewRepresentable {
    func makeUIView(context: Context) -> FixedAccessibilityTextView {
        FixedAccessibilityTextView()
    }
    
    func updateUIView(_ uiView: FixedAccessibilityTextView, context: Context) {
        // 你的更新逻辑
    }
}

3. 临时禁用模拟器辅助功能 #

如果暂时无法修复代码，可在模拟器中关闭辅助功能：

• 打开模拟器「设置」→「辅助功能」，关闭VoiceOver、Switch Control等选项，但这只是临时方案，无法从代码层面解决问题。

4. 更新Xcode和模拟器版本 #

该问题可能是旧版本模拟器的bug，尝试更新到最新的Xcode和iOS模拟器版本，看是否已被苹果修复。

内容的提问来源于stack exchange，提问作者reza23