Question

我正在使用SwiftUI和Combine开发一个应用程序。我遇到几次尝试打开/关闭黑暗模式时发生的崩溃。控制台中打印的日志显示：

precondition failure: attribute failed to set an initial value: 78

在堆栈跟踪中没有与崩溃起源有关的有价值的信息。

* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
    frame #0: 0x00000001ba5d9ec4 libsystem_kernel.dylib`__pthread_kill + 8
    frame #1: 0x00000001ba4f9c00 libsystem_pthread.dylib`pthread_kill$VARIANT$armv81 + 192
    frame #2: 0x00000001ba449844 libsystem_c.dylib`abort + 100
    frame #3: 0x00000001e4eae548 AttributeGraph`AG::precondition_failure(char const*, ...) + 188
    frame #4: 0x00000001e4e80194 AttributeGraph`AG::Graph::UpdateStack::update() + 1320
    frame #5: 0x00000001e4e80308 AttributeGraph`AG::Graph::update_attribute(unsigned int, bool) + 372
    frame #6: 0x00000001e4e83874 AttributeGraph`AG::Graph::input_value_ref_slow(unsigned int, unsigned int, AGTypeID, bool*) + 212
    frame #7: 0x00000001f0ca08d8 SwiftUI`generic specialization <SwiftUI.Color._Resolved> of SwiftUI.AnimatableAttribute.update(context: inout AttributeGraph.AttributeContext<SwiftUI.AnimatableAttribute<A>>) -> () + 492
    frame #8: 0x00000001f0bf7d80 SwiftUI`merged partial apply forwarder for generic specialization <SwiftUI.Color._Resolved> of  + 20
    frame #9: 0x00000001e4e80044 AttributeGraph`AG::Graph::UpdateStack::update() + 984
    frame #10: 0x00000001e4e80308 AttributeGraph`AG::Graph::update_attribute(unsigned int, bool) + 372
    frame #11: 0x00000001e4e84ff0 AttributeGraph`AG::Subgraph::update(unsigned int) + 548
    frame #12: 0x00000001f093cde8 SwiftUI`SwiftUI.ViewGraph.(runTransaction in _D63C4EB7F2B205694B6515509E76E98B)(in: __C.AGGraphRef) -> () + 220
    frame #13: 0x00000001f093d114 SwiftUI`closure #1 (__C.AGGraphRef) -> (prefs: Swift.Bool, idealSize: Swift.Bool, outputs: SwiftUI.ViewGraph.Outputs) in SwiftUI.ViewGraph.updateOutputs(at: SwiftUI.Time) -> () + 116
    frame #14: 0x00000001f093ce9c SwiftUI`SwiftUI.ViewGraph.updateOutputs(at: SwiftUI.Time) -> () + 116
    frame #15: 0x00000001f0c5a6b8 SwiftUI`closure #1 () -> () in closure #1 () -> () in (extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> () + 960
    frame #16: 0x00000001f0c5a120 SwiftUI`closure #1 () -> () in (extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> () + 576
    frame #17: 0x00000001f0c4f9a8 SwiftUI`(extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> () + 400
    frame #18: 0x00000001f0852c30 SwiftUI`closure #1 () -> () in SwiftUI._UIHostingView.requestImmediateUpdate() -> () + 68
    frame #19: 0x00000001f084ed10 SwiftUI`reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_unowned @convention(block) () -> () + 24
    frame #20: 0x0000000100eb97fc libdispatch.dylib`_dispatch_call_block_and_release + 24
    frame #21: 0x0000000100ebabd8 libdispatch.dylib`_dispatch_client_callout + 16
    frame #22: 0x0000000100ec8c34 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 1316
    frame #23: 0x00000001ba75f3a8 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
    frame #24: 0x00000001ba75a39c CoreFoundation`__CFRunLoopRun + 2004
    frame #25: 0x00000001ba7598a0 CoreFoundation`CFRunLoopRunSpecific + 464
    frame #26: 0x00000001c46b1328 GraphicsServices`GSEventRunModal + 104
    frame #27: 0x00000001be84a740 UIKitCore`UIApplicationMain + 1936
  * frame #28: 0x0000000100a1452c WForcast`main at AppDelegate.swift:12:7
    frame #29: 0x00000001ba5e4360 libdyld.dylib`start + 4

我已经浏览了很多在线讨论话题（Stackoverflow，Apple论坛等），但是我找不到足够的信息来了解崩溃的原因。

此错误开始出现时，大多数工作已在HomeView类中完成。我已经通过在上一次提交中测试代码来确认这一点。

以下是视图类。

struct HomeView: View {

    @ObservedObject private(set) var viewModel: HomeViewModel

    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Image(systemName: "location")
                    .resizable()
                    .frame(width: 12, height: 12, alignment: .trailing)
                    .padding(.leading)
                Text(viewModel.model.cityFullName)
                    .font(.headline)
                    .fontWeight(.light)
                Spacer()
                Circle()
                    .frame(width: 8, height: 8, alignment: .trailing)
                    .foregroundColor(viewModel.mode == .offline ? .red : .green)
                Text(viewModel.mode.rawValue)
                    .font(.headline)
                    .fontWeight(.light)
                    .padding(.trailing)
            }
            .padding(.vertical)
            List(viewModel.model.weatherDateMap) { item in
                DailyForcastView(viewModel: DailyForcastViewModel(model: item))
                Spacer()
            }
        }
    }
}

以下是我的视图模型：

class HomeViewModel: ObservableObject {

    @Published private(set) var model: CityWeatherModel
    @Published private(set) var mode: AppMode = .offline

    init(model: CityWeatherModel) {
        self.model = model
    }
}

以下是我的数据模型：

struct CityWeatherModel {
    var weatherDateMap: [WeatherDateMap]
    var city: City?

    var cityFullName: String {
        return city?.fullName ?? ""
    }
}

struct WeatherDateMap: Identifiable {
    let id: UUID = UUID()
    let date: Date
    let forcasts: [Forcast]
}

struct City: Decodable {
    let id: Int?
    let name: String?
    let country: String?

    var fullName: String {
        get {
            guard let name = self.name else { return "" }
            return name + ((country != nil) ? ", \(country ?? "")"  : "")
        }
    }
}

struct Forcast: Decodable, Identifiable {
    let id: UUID = UUID()
    let dateInterval: Int?
    let date: Date?
    var weatherParticular: WeatherParticular?
    let weather: [Weather?]?

    enum CodingKeys: String, CodingKey {
        case dateInterval = "dt"
        case date  = "dtTxt"
        case weatherParticular = "main"
        case weather
    }
}

struct WeatherParticular: Decodable {
    var temp: Double?
    let tempMin: Double?
    let tempMax: Double?
    let pressure: Double?
    let seaLevel: Double?
    let humidity: Double?

    mutating func updateTemp(_ temprature:  Double?) {
        temp = temprature
    }
}

struct Weather: Identifiable, Decodable {
    let id: Int?
    let main: String?
    let description: String?
    let icon: String?
}

以下是用户界面的屏幕截图：

有人遇到过这个吗？如果是，那是什么问题，您是如何解决的？

前提条件失败：属性无法设置初始值：78 | iOS 13.2.2 | XCode 11.2.1

0 个答案: