Rx BehaviorRelay doesnt keep the data when return from a view

Question

I have an app that have 3 views and a service logic layer. The services is sending messagings all the time to all this views.What I do to control all this data was use RxBehaviorRelay.

To this point all works great, I match the variables with the services layer and I am receiving data in the ViewController 1, 2 and 3.

The problem comes when I am on the view2 and then go to view3 and return to view2. On this return I lost all the changes and the BehaviorRelay object is like the beginning.

My code in the view1 is like this one

class View1: UIViewController {
    var service: ServiceModel? = ServiceModel()
    
    var observableView1 = BehaviorRelay(value: [Object]())
    var observableView2 = BehaviorRelay(value: [Object]())
    
    override func viewDidLoad() {
        service!.observableView1 = self.observableView1
        service!.observableView2 = self.observableView2
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let destination = segue.destination as! View2
        destination.observableView2 = self.observableView2
    }
}

Code of view2

class View2: UIViewController {
    let disposeBag = DisposeBag()
    
    var observableView2 = BehaviorRelay(value: [Object]())
    
    override func viewDidLoad() {
        fillTable()
    }
    
    func fillTable() {
        observableView2.asObservable().bind(to: tvData.rx.items) { (tableview, row, data) in
            //code to fill the table
        }.disposed(by: disposeBag)
    }
}

On the service layer I only receive the changes and put in the BehaviorRelay object.

observableView2.accept(changes)
observableView1.accept(changes)

As I said I obtain all the changes in the view2 but when I move to view3 and return to view2, the changes gone.

Sorry for my english. Thanks

Daniel T. · Answer 1 · 2020-11-28T20:35:57.093

All relays, subjects and observables should always be declared using let, never with var. Once you make this fix, you will notice why you are loosing your changes.

Based on your description, I would expect something more like:

final class Service { 
    private let _observableView1 = BehaviorRelay(value: [Object]())
    private let _observableView2 = BehaviorRelay(value: [Object]())
    let observableView1: Observable<[Object]>
    let obserrvableView2: Observable<[Object]>
    init() { 
        observableView1 = _observableView1.asObservable()
        observableView2 = _observableView2.asObservable()
    }
}

Then pass the Service to View 2, or subscribe to the service inside the prepare method.

Rx BehaviorRelay doesnt keep the data when return from a view

1 Answers1