Question

场景： 我希望能够通过@Published值（networkMessage和hasAlert）从Observable对象显示Alert（）。

缺少网络连接时应触发此警报。
通过 here

主机视图，其中显示Alert（）：

import SwiftUI

struct EndPointView: View {
    @EnvironmentObject var settings: Settings
    @ObservedObject var standardWeatherReport = StandardWeatherReport()
    @ObservedObject var publishedWeatherReport = PublishedWeatherReport()
    @ObservedObject var pepBoy = PepBoy()
    @ObservedObject var postMan = PostMan()

    var body: some View {
        Form {
            Text("Chosen One: \(settings.endpointSection)")
            Text("Row Two")
            Text("Row Three")
            Text("Row Four")

        }.onAppear {
            self.acquireData()
        }
        .alert(isPresented: $standardWeatherReport.hasAlert, content: { () -> Alert in
            Alert(title: Text(verbatim: standardWeatherReport.networkMessage!))
        })
    }

    func acquireData() {
        let chosenEndPoint = EndPoints(rawValue: settings.endpointSection)
        switch chosenEndPoint {
            case .standardWeather:
                standardWeatherReport.doStandard()
            case .publishedWeather:
                publishedWeatherReport.doPublish()
            case .postman:
                postMan.doPublishPostMan()
            case .publishpepboy:
                pepBoy.doPublishPep()
            case .none:
                print("none")
        }
    }
}

可观察对象最初通过case .failure（让anError）触发了Alert（）：

import Foundation

class PublishedWeatherReport: ObservableObject {
    @Published var networkMessage: String?
    @Published var hasAlert = false
    @Published var weatherReport: String?

    func doPublish() {
        let url = EndPoint.weather.path()
        var request = URLRequest(url: EndPoint.weather.path()!)
        request.httpMethod = "GET"
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")

        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase

        // Publisher:
        let remoteDataPublisher = URLSession.shared.dataTaskPublisher(for: url!)
            // the dataTaskPublisher output combination is (data: Data, response: URLResponse)
            .map { $0.data }
            .decode(type: Sample.self, decoder: decoder)
            .receive(on: DispatchQueue.main)
            .eraseToAnyPublisher()

        // Subscriber:
        sub = remoteDataPublisher // ...must assign to an iVar to keep alive.
            .sink(receiveCompletion: { completion in
                switch completion {
                case .finished:
                    break
                case .failure(let anError):
                    self.networkMessage = anError.localizedDescription
                    self.hasAlert = true.  // ... unable to host Alert().
                }
            }, receiveValue: { someValue in
                print(".sink() received \(someValue)")
            })
    }
}

问题：为什么我没有通过

收到此alert（）

(isPresented: $standardWeatherReport.hasAlert)?

Answer 1

standardWeatherReport.hasAlert并非来自PublishedWeatherReport类。 StandardWeatherReport类在哪里

Answer 2

我混合了两个出版商。
因此，相关警报无法正常运行。

另外，我还有多个警报运算符，每个发布者一个。
这是一个错误的设计：每个主机只允许一（1）个警报操作员；否则，第二个.alert运算符将覆盖前一个运算符。

因此，如果一个警报处于活动状态，那么随后一个非活动警报操作员将立即取消该警报。

无法显示来自可观察对象的警报

2 个答案: