While data binding and two-way data binding are not required to use MVVM, you saw in the previous example that binding actions and values is tedious, a source of boilerplate, and prone to errors.
While data binding is usually found in Reactive programming frameworks, it revolves around a simple object: the Observable object. The responsibility of an observable is to call the observers whenever a change in the internal value occurs.
We'll implement Observable as a generic class, as it should be able to wrap any kind of object:
class Observable<Type> {
typealias Observer = (Type) -> ()
typealias Token = NSObjectProtocol
private var observers = [(Token, Observer)]()
var value: Type {
didSet {
notify()
}
}
init(_ value: Type) {
self.value = value
}
@discardableResult
func bind(_ observer: @escaping Observer) -> Token {
defer { observer(value) }
...