Strategy策略模式

一个类的行为或其算法可以在运行时更改

using UnityEngine;
using System.Collections;

namespace StrategyPatternExample2
{
    public class StrategyPatternExample2 : MonoBehaviour
    {
        Animal sparky = new Dog();
        Animal tweety = new Bird();
        void Start()
        {

            Debug.Log("Dog: " + sparky.TryToFly());
            Debug.Log("Bird: " + tweety.TryToFly());

            // change behaviour of dog
            

            
        }
        private void Update()
        {
            if (Input.GetKeyDown(KeyCode.A))
            {
                sparky.SetFlyingAbility(new ItFlys());
                Debug.Log("Dog: " + sparky.TryToFly());
                Debug.Log("Bird: " + tweety.TryToFly());
            }
        }
    }


    // Using Interfaces for decoupling
    // putting behaviour that varies in different classes
    public interface IFly
    {
        string Fly();
    }

    // Class that holds behaviour for objects that can fly
    class ItFlys : IFly
    {
        public string Fly()
        {
            return "Flying high";
        }
    }

    // Class that holds behaviour for objects that can not fly
    class CantFly : IFly
    {
        public string Fly()
        {
            return "I can't fly";
        }
    }

    class FlyingSuperFast : IFly
    {
        public string Fly()
        {
            return "Fly super fast";
        }
    }


    // Classes that hold an instance of the behaviours above:
    public class Animal
    {
        // hereby adding the behaviour
        // it also can change that way
        public IFly flyingType;

        public string TryToFly()
        {
            return flyingType.Fly();
        }

        public void SetFlyingAbility(IFly newFlyingType)
        {
            this.flyingType = newFlyingType;
        }
    }

    // derived objects that vary from the base Animal:
    public class Dog : Animal
    {
        public Dog()
        {
            flyingType = new CantFly();
        }
    }

    public class Bird : Animal
    {
        public Bird()
        {
            flyingType = new ItFlys();
        }
    }
}

策略模式确实和状态模式有相似之处，但又不太一样，状态模式旨在根据条件进行状态切换，策略模式则是直接替换行为或者方法