joi, 20 mai 2010

[DesignPattern] State Pattern

State Pattern

  • When the state inside an object changes, it can change its behavior by switching to a set of different operations
  • The Context represents information that is mostly fixed, whereas the State can change between the available options as the program progresses
  • The State pattern relies on simple mechanisms: interfaces and aggregation.
  • The States can be classes, or if they are quite simple—without much data— they can be implemented as delegates.

  • Context: A class that maintains an instance of a State that defines the current context and the interface of interest to clients
  • IState: Defines an interface for a particular state of the Context
    - The State has full access to the data in the Context.
    - At any point, either the Context or the active State can decide that it is time to switch states.
  • StateA and StateB: Classes that implement behavior associated with a state of the Context

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