The observer pattern is a software design pattern that allows an object, usually called the subject, to maintain a list of dependents, called observers, and notify them automatically of any state-changes. Many languages have this pattern either built-in or in their standard libraries.
Examples:
C# has the concept of Observable in the standard .NET library. Also it has the concept of delegates.
Although Dart doesn’t have it, in Flutter we have the SetState method which automatically notifes any observer, and it is mainly used to refresh the UI.
It looks like this:
Press enter or click to view image in full size
A breakdown of this diagram:
First there is the Observable, this could be an interface, the object which is to be observed. The observable holds a list of observers.
The Observer, which sends out a message to the observers. This could also be an interface.
The ConcreteObservable, the concrete class which holds the state. If anything changes in the state, the setState method is called, which in turn…
