How to have a subject in RxSwift push values to itself without creating an infinite loop - swift

Question

I have a UITableView, which I want to put into an editing state if certain conditions are met. The primary way to toggling edit is through an edit button.
So the view elements I have are
let tableView = UITableView()
let editButton = UIButton()
And whether the tableView should be in editing mode is fed from:
let editing = BehaviorSubject(value: false)
Which will be hooked up to the tableView using something like:
editing.subscribeNext { isEditing in
tableView.setEditing(isEditing, animated: true)
}
When the edit button is tapped, I want that to push a new value to editing, that is the negation of the most recent value sent to editing. The most recently value may have been set by a tap on editButton, or it may have come from somewhere else.
I don't understand how to combine the stream for the button press with the stream for editing in such a way that allows this without an infinite loop e.g.
Obervable.combineLatest(editButton.rx_tap.asObservable(), editing) { _, isEditing in
editing.onNext(!isEditing)
}
I'm aware that the tableView has an editing property, but I don't want to rely on that as I am looking for a more general solution that I can re-use elsewhere. I'm also not looking to track the value of isEditing in an instance var, or even as a Variable(), as I am looking for a stateless, stream based solution (if this is at all possible).
Thank you!

Answer 1

With some help from the RxSwift GitHub issues forum I've now worked it out :). The key was withLatestFrom. I've included an example of this below in case it will help anyone else. editButton is the primary way to trigger editing mode on or off, and I've included an event sent via tableView.rx_itemSelected as an additional input example (in this case, I want editing to end any time an item is selected).
let isEditing = BehaviorSubject(value: false)
let tableView = UITableView()
let editButton = UIButton()
tableView.rx_itemSelected
.map { _ in false }
.bindTo(isEditing)
editButton.rx_tap.withLatestFrom(isEditing)
.map { !$0 }
.bindTo(isEditing)
isEditing.subscribeNext { editing in
tableView.setEditing(editing, animated: true)
}
Note: This solution sends .Next(false) to isEditing every time an item is selected, even if the table isn't currently in editing mode. If you feel this is a bad thing, and want to filter rx_itemSelected to only send .Next(false) if the table is actually in editing mode, you could probably do this using a combination of withLatestFrom and filter.

Answer 2

What if you define editing as a Variable instead of a BehaviourSubject. A Variable cannot error out which makes sense in this case. The declaration would look like this:
let editing = Variable(value: false)
You could subscribe to a button tap and change the value of editing to the negated current one:
editButton.rx_tap.asObservable().subscribeNext { editing.value = !editing.value }
With changing the value property of editing this method is called
editing.subscribeNext { isEditing in
tableView.setEditing(isEditing, animated: true)
}
All of this is not tested, but might lead you in the right direction for the right solution.