Flutter patterns

1.1. The object which is being watched is called the subject. The objects which are watching the state changes are called observers or listeners .

Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its depenedent objects are to be notified automatically . Observer pattern falls under behavioral pattern category.

The observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

If available, the observer function is called for every time step in the iteration. It can be used for calculations “on the fly” to reduce memory of saved data, for user-specified animation or for logging purposes . If the value returned by observer is a vector, than resulting out will be a data.