onReceive callback not executing-CodePudding

So I am working on a view in SwiftUI which will update its state when an event is published.

The view looks like this:

struct MyView: View {
    
    @EnvironmentObject var dataSource: DataSource
    @State var data: [Model] = []
    

    func refreshData() {
        self.data = dataSource.getData()
    }
    
    var body: some View {
        VStack {
            List(self.data) { model in
                Row(model: model)
            }
        }
        .onAppear {
            self.refreshData()
        }
        .onReceive(self.dataSource.didUpdate) { _ in
            print("on receive")
            self.refreshData()
        }
    }
}

class DataSource: ObservableObject {
    var didUpdate: PassthroughSubject<Model,Never> ...
}

So with this setup, the onAppear block is called and works as expected. But the onReceive callback is never called. I have been able to verify that .send is being called correctly on the DataSource.didUpdate subject, but it appears the subscriber is not being notified.

Is there something I am missing to make this work?

CodePudding user response：

For the subscriber to be notified, it needs to listen to the "binding" rather than the variable itself. Changing it to

.onReceive(self.dataSource.$didUpdate)

should fix the issue. You can read up more here.

CodePudding user response：

As you are correctly declaring your DataSource as an observable object class, what you need now is to use the @Published property wrapper on you didUpdate variable. Then, with SwiftUI you can listen to it using .onChange(of:) { }. Just note that it does not work with computed vars: in such case, use the computed var to update the published var. Also, I assume you are correctly injecting your model instance in the environment (otherwise it will never work).

Like this:

struct MyView: View {
    
    @EnvironmentObject var dataSource: DataSource   // Remember to inject the specific instance in the environment
    @State var data: [Model] = []
    

    func refreshData() {
        self.data = dataSource.getData()
    }
    
    var body: some View {
        VStack {
            List(self.data) { model in
                Row(model: model)
            }
        }
        .onAppear {
            self.refreshData()
        }
//        .onReceive(self.dataSource.didUpdate) { _ in
//           print("on receive")
          .onChange(of: dataSource.didUpdate) { _ in     // Listen to changes in ObservableObject property that publishes
              print("on change")
              self.refreshData()
        }
    }
}

class DataSource: ObservableObject {

    // Note the property wrapper, but it does not work with computed vars:
    // in such case, use the computed var to update the published var.
    // Also: update it only in the main thread!
    @Published var didUpdate: PassthroughSubject<Model,Never> ...
}