如何在SwiftUI中不使用按钮更新@EnvironmentObject？

Question

What I am trying to accomplish here is when filterListGraph is updating data, iconArray will add the amount and then update data too. I was trying to use .onAppear(), but it does not work properly as I expected since it adds amount only once when GraphView appears (I need to exit from GraphView and go back in order to update data). Is that possible to add amount into iconArray in GraphView and then update it?

struct IconStruct: Identifiable {
let id = UUID()
var icon: String
var amount: Double
var color: Color
var index: Int
}

class UserSettings: ObservableObject {
@Published var iconArray: [IconStruct] = [IconStruct(icon: "FoodIcon", amount: 0, color: Color(.red), index: 0),
                                          IconStruct(icon: "ClothesIcon", amount: 0, color: Color(.blue), index: 1),
                                          IconStruct(icon: "SportIcon", amount: 0, color: Color(.yellow), index: 2)]

}

struct GraphView: View {

var dateFormatter: DateFormatter {
    let formatter = DateFormatter()
    formatter.dateStyle = .long
    return formatter
}

@EnvironmentObject var settings: UserSettings

@State private var fromDate = Calendar.current.date(byAdding: .month, value: -1, to: Date())!
@State private var toDate = Date()
@State private var selectedType = "type != %@"
@State private var selectedDate = true
@State private var searchText = ""
@State private var isNavigationBarHidden: Bool = true

var body: some View {
    ScrollView {
        VStack {

            ForEach(settings.iconArray) { row in
                Text(row.amount.description)
            }

            HStack {
                Picker("", selection: $selectedType) {
                    Text("Expense").tag("type != %@")
                    Text("Income").tag("type == %@")
                }
                .pickerStyle(SegmentedPickerStyle())

            }

            HStack {
                Picker("", selection: $selectedDate) {
                    Text("From: \(dateFormatter.string(from: fromDate))").tag(true)
                    Text("To: \(dateFormatter.string(from: toDate))").tag(false)
                }
                .pickerStyle(SegmentedPickerStyle())
            }

            DatePicker("", selection: selectedDate ? $fromDate : $toDate, displayedComponents: .date)
                .labelsHidden()
        }

        PieChartRow(data: settings.iconArray, backgroundColor: .white)
            .frame(width: 300, height: 300)

        ForEach(settings.iconArray.sorted { $0.amount > $1.amount }) { icon in
            filterListGraph(type: self.selectedType, icon: icon.icon, from: self.fromDate, to: self.toDate, iconIndex: icon.index)
        }
    }
}
}


struct filterListGraph: View {
@Environment(\.managedObjectContext) var context
var financeArray: FetchRequest<Finance>
var type: Bool
var icon: String
var iconIndex: Int

@EnvironmentObject var settings: UserSettings

var amount: Double {
    return financeArray.wrappedValue.map { $0.wrappedAmount }.reduce(0,+)
}

// var amount: Double {
// self.settings.iconArray[self.iconIndex].amount = self.financeArray.wrappedValue.map { $0.wrappedAmount }.reduce(0,+)
//    return self.settings.iconArray[self.iconIndex].amount
// }

var body: some View {
    VStack {
        if amount != 0 {
            CellContainer(image: icon, label: nil, amount: amount.description, type: type)
        }
//        .onAppear() {
//           self.settings.iconArray[self.iconIndex].amount = self.financeArray.wrappedValue.map { $0.wrappedAmount }.reduce(0,+)
//        }
    }
}

init(type: String, icon: String, from: Date, to: Date, iconIndex: Int) {
    self.iconIndex = iconIndex
    self.icon = icon
    if type == "type == %@" {
        self.type = true
    } else {
        self.type = false
    }
    financeArray = FetchRequest<Finance>(
        entity: Finance.entity(),
        sortDescriptors: [
            NSSortDescriptor(keyPath: \Finance.date, ascending: true)
        ], predicate:
        NSCompoundPredicate(notPredicateWithSubpredicate: NSCompoundPredicate.init(type: .or, subpredicates: [
            NSPredicate(format: type, "false"),
            NSPredicate(format: "icon != %@", icon),
            NSPredicate(format: "date < %@ OR date >= %@", (Calendar.current.startOfDay(for: from) as NSDate), Calendar.current.date(byAdding: .day, value: 1, to: to)! as NSDate )
        ]))
    )
}
}

Answer 1

If I understood correctly, you need to track variable amount of array in UserSettings . I can't run your code, because there are some whitespaces, so there are few tips, hope they may help you. For both you need use Combine framework (you may read about it here )

1. create variable amount strictly in UserSettings and change it while your array cnahges:

import Combine

class UserSettings: ObservableObject {

    @Published var amount: Double = 0.0
    @Published var iconArray: [IconStruct] {
        didSet {
            self.amount = Double(iconArray.count)
        }

    }

    init() {
        self.iconArray = [IconStruct(icon: "FoodIcon", amount: 0, color: Color(.red), index: 0),
        IconStruct(icon: "ClothesIcon", amount: 0, color: Color(.blue), index: 1),
        IconStruct(icon: "SportIcon", amount: 0, color: Color(.yellow), index: 2)]
    }

}

2. But because I'm not sure that code in first tip is enough, you may add AnyPublisher to settings and after that subscribe for it:

class UserSettings: ObservableObject {

    @Published var amount: Double = 0.0
    @Published var iconArray: [IconStruct] {
        didSet {
            self.amount = Double(iconArray.count)
        }

    }

    var trackingAmount: AnyPublisher<Double, Never> {
        return $amount
            .eraseToAnyPublisher()
            // or something else you need, read about Combine
    }


    init() {
        self.iconArray = [IconStruct(icon: "FoodIcon", amount: 0, color: Color(.red), index: 0),
        IconStruct(icon: "ClothesIcon", amount: 0, color: Color(.blue), index: 1),
        IconStruct(icon: "SportIcon", amount: 0, color: Color(.yellow), index: 2)]
    }

}

// here the key idea is .onReceive(settings.trackingAmount)
struct filterListGraph: View {

    @EnvironmentObject var settings: UserSettings

    var body: some View {
        Text("some another view").onReceive(settings.trackingAmount) { _ in
            // change what you need
        }
    }

}