How can I select all item at once using RxSwift operator? - swift

Question

Let's say I have a table view to present products.
Here is my viewModel:
ProductViewModel.swift
var selectedObserver: AnyObserver<Product>
var state: Driver<Set<Product>>
var selectedSubject = PublishSubject<Product>()
self.selectedObserver = selectedSubject.asObserver()
self.state =
selectedSubject.asObservable()
.scan(Set()) { (acc: Set<Product>, item: Product) in
var acc = acc
if acc.contains(item) {
acc.remove(item)
} else {
acc.insert(item)
}
return acc
}
.startWith(Set())
.asDriver(onErrorJustReturn: Set())
self.isSelectedAll = Driver
.combineLatest(
self.state.map { $0.count },
envelope.map { $0.products.count })
.debug()
.map { $0.0 == $0.1 }
As you see, every time I select an object, I will scan it into the state observable, so the cell can then observe the state change.
Here is the RxSwift binding between cell and viewModel:
ProductViewController.swift
self.viewModel.deliveries
.drive(self.tableView.rx.items(cellIdentifier: DeliveryTableViewCellReusableIdentifier, cellType: DeliveryTableViewCell.self)) { (_, item, cell) in
cell.bind(to: self.viewModel.state, as: item)
cell.configureWith(product: item)
}
.disposed(by: disposeBag)
self.tableView.rx.modelSelected(Product.self)
.asDriver()
.drive(self.viewModel.selectedObserver)
.disposed(by: disposeBag)
ProductCell.swift
func bind(to state: Driver<Set<Product>>, as item: Product) {
state.map { $0.contains(item) }
.drive(self.rx.isSelected)
.disposed(by: rx.reuseBag)
}
Well, so far so good.
Now my question is how can I make a select all action e.g. tapping a select all button, so that all product will be somehow scan into states?

Answer 1

There is, of course, more ways to do this. One that comes to my mind is having two different events for single selection vs. select all, unifying them in one enum, eg. SelectionEvent, merging them and passing that to the scan so that in the scan method you can differentiate between them.
Rough example, following your code:
var selectedObserver: AnyObserver<Product>
var state: Driver<Set<Product>>
var selectedSubject = PublishSubject<Product>()
var selectedAllSubject = PublishSubject<Product>() // Added
var selectedAllObserverObserver: AnyObserver<Void> // Added
self.selectedObserver = selectedSubject.asObserver()
self.selectedAllObserverObserver = selectedAllSubject.asObserver()
enum SelectionEvent {
case product(Product)
case all([Product])
}
self.state = Observable.of(
selectedSubject.map { SelectionEvent.product($0) },
// I figured envelope is observable containing all products.
selectedAllSubject.withLatestFrom(envelope.map { $0.products }).map { SelectionEvent.all($0) }
).merge()
.scan(Set()) { (acc: Set<Product>, event: SelectionEvent) in
var acc = acc
// now you can differentitate between events
switch event {
case .product:
if acc.contains(item) {
acc.remove(item)
} else {
acc.insert(item)
}
case .all(let all):
acc = all
}
return acc
}
.startWith(Set())
.asDriver(onErrorJustReturn: Set())
I hope this helps.