A little consideration of strategic mode

Speaking of strategic mode , When talking about my thinking about its use , First look at his existing axioms ：

Concept definition ： The strategy pattern defines a series of algorithms , And encapsulate each algorithm , And make them interchangeable , Let the algorithm be independent of the client using it

Application scenarios ： Multiple ways to deal with the same problem , The difference in behavior   

UML chart ：

There are three concepts involved here ： The policy abstract class itself , Holders of abstract classes , Specific strategies of abstract classes （ It can be understood as implementing subclasses ）

for instance ： stay iOS A news of app On the news list cell style , There may be three kinds ：a： Plain text display   b： Pure picture display     c： Video display     abc The specific implementation of the three styles is the specific strategy , Abstract style classes are policy abstract classes , Suppose that UITableViewCell To load these styles ,UITableViewCell It can be the holder of an abstract class . When using styles , By calling the load style method of the abstract class , And pass parameters to instantiate different styles .

reflection ：1. Using the policy pattern , You have to know all the policy classes , And decide which policy class to use ？

         2. Policy patterns can use inheritance as appropriate , Transfer the common part to the abstract class , But it will cause if you don't use abstract classes , It will lead to the incompleteness of the public part of the strategy method ？ So we should pay attention to the appropriate trade-offs ？

         3. Behavior classes that use policy methods （ Judge where to use ） It can be completely separated from specific strategies and methods . In this way, the strategy and method can evolve independently ？

         4. The policy pattern results in an independent policy class for each specific implementation , And in actual development , Several strategies and methods may be completed in a class in minutes , If you use the policy mode development, there will be many more files , Many kinds , Resulting in extended development time , How to choose ？