Swift 5：ObservedObject 未更新

Question

I've created an ObservableObject class called ActiveQuiz with info I want to share across multiple views:

import Foundation

class ActiveQuiz: ObservableObject{
    @Published var iterator = 0
    @Published var questions = createQuiz()
}

In one of the views I display text, that if tapped on will increase the iterator which in turn updates the text as it has moved on to the next entry in the questions array:

import SwiftUI

struct Question: View {
    @ObservedObject var activeQuiz = ActiveQuiz()

    var body: some View {
        Text(self.activeQuiz.questions[self.activeQuiz.iterator].countryInfo.capital)
            .font(.title)
            .onTapGesture(perform: {
                // increase iterator by 1 unless it's at the end, then put back to 0
                self.activeQuiz.iterator = self.activeQuiz.iterator + 1 == self.activeQuiz.questions.count ? 0 : self.activeQuiz.iterator + 1
            } )
    }
}

In the other view I have a count which displays where the iterator is:

import SwiftUI

struct QuestionCounter: View {
    @ObservedObject var activeQuiz = ActiveQuiz()

    var body: some View {
        Text(String(self.activeQuiz.iterator + 1) + "/" + String(self.activeQuiz.questions.count))
    }
}

The text from the first view is updating as expected but the iterator from the second view stays at the initial 1/x.

Question : Being new the Swift, I don't understand why the shared state of the ObservableObject ActiveQuiz isn't updating across all view that are "observing" it. Also in being new to swift, I apologize if I've not included any info needed to answer the question that I'm not aware of.

Answer 1

It's not clear, how you use these views together, maybe for others it will be helpful to add ContentView , for example. As I see, you use 2 different ActiveQuiz instances. So your Question struct have 1 instance and you update it's iterator and QuestionCounter has it's own instance, which is not updating from the first one. I think the solution should be to use @EnvironmentObject for both structs, like this (I simplified your example because of lack of code):

import SwiftUI
import Combine

class ActiveQuiz: ObservableObject {
    @Published var iterator = 0
}

struct UsingEnvironmentObject: View {

    @EnvironmentObject var activeQuiz: ActiveQuiz
    var body: some View {
        VStack {

            Question() // it will take EnvironmentObject from parent
            QuestionCounter() // this one will take the same EnvironmentObject from parent

        }
    }
}

// more representative solution
struct UsingEnvironmentObject: View {

    @ObservedObject var activeQuiz = ActiveQuiz()

    var body: some View {
        VStack {
            // here you see, that both structs use one instance
            Question()
                .environmentObject(activeQuiz)
            QuestionCounter()
                .environmentObject(activeQuiz)

        }
    }
}

struct Question: View {

    @EnvironmentObject var activeQuiz: ActiveQuiz

    var body: some View {
        Text("some text from question")
            .font(.title)
            .onTapGesture(perform: {
                // increase iterator by 1 unless it's at the end, then put back to 0
                self.activeQuiz.iterator = self.activeQuiz.iterator + 1 == 10 ? 0 : self.activeQuiz.iterator + 1
            } )
    }
}

struct QuestionCounter: View {
    @EnvironmentObject var activeQuiz: ActiveQuiz

    var body: some View {
        Text(String(self.activeQuiz.iterator + 1) + "/10")
    }
}



struct UsingEnvironmentObject_Previews: PreviewProvider {
    static var previews: some View {
        UsingEnvironmentObject()
        .environmentObject(ActiveQuiz())
    }
}

and you will achieve this: