设计模式-策略模式

策略模式：定义一系列的算法，将每个算法分别封装起来，让它们可以互相替换。

策略模式用于算法的自由切换和扩展，它是使用较为广泛的设计模式之一。策略模式对应于解决某一问题的一个算法族，允许用户从该算法中任选一个算法解决某一问题，同时可以方便地更换算法或者增加新算法。

策略模式实现了算法定义和算法使用分离，它通过继承和多态的机制实现对算法族的使用和管理，是一个简单实用的设计模式。

//以下使用的是顶级语句
//未使用依赖注入的调用
//var ef = new EFCoreRepository();
//var redis = new RedisRepostitory();
//var appService = new AppService(redis);
//appService.Create(null);


//使用依赖注入的调用 
using Microsoft.Extensions.DependencyInjection;

var services=new ServiceCollection(); //服务容器,依赖注入容器,IoC控制反转
services.AddScoped<IRepository,EFCoreRepository>();//添加作用域
//services.AddScoped<IRepository, RedisRepostitory>();//添加作用域
services.AddScoped<AppService>();

var builder=services.BuildServiceProvider();//生成服务提供程序

var  appService=builder.GetRequiredService<AppService>();//获取所需服务
appService.Create(null);
public class EFCoreRepository : IRepository //EF仓储
{
    public void Add(object entity)
    {
        Console.WriteLine("EF Core的仓储");
    }
}

public class RedisRepostitory : IRepository
{
    public void Add(object entity)
    {
        Console.WriteLine("Redis的仓储");

    }
}
public interface IRepository  //仓储
{
    void Add(object entity);
    
}


class AppService
{
    private readonly IRepository _repository;
    public AppService(IRepository repository)
    { 
        this._repository = repository;
    }
    public void Create(object entity)
    {
        _repository.Add(entity);
    }
}

下面是一个电影票根据不同用户类型打折的实例

using Microsoft.Extensions.DependencyInjection;
using System.Globalization;
using System.Reflection;
using System.Runtime.CompilerServices;

var service = new ServiceCollection();
service.AddScoped<IStrategy, StudentStrategy>()
       .AddScoped<AppService>();
var builder = service.BuildServiceProvider();
var appSerivce=builder.GetRequiredService<AppService>();
appSerivce.Price = 50;
Console.WriteLine("电影票原价50元");
Console.WriteLine(appSerivce.Price);




class StudentStrategy : IStrategy
{
    readonly string _name = "学生";
    readonly Double _discount = 0.8;

    public decimal Calculate(decimal price)
    {

        Console.WriteLine(_name + "票:");
        return price * (decimal)_discount;
    }

}
class ChildrenStrategy : IStrategy
{
    readonly string _name = "儿童";
    readonly Double _discount = 10;

    public decimal Calculate(decimal price)
    {
        Console.WriteLine(_name + "票:");
        return price * (decimal)_discount;
    }
}
class VIPStrategy : IStrategy
{
    readonly string _name = "VIP";
    readonly Double _discount = 0.5;
    public decimal Calculate(decimal price)
    {
        Console.WriteLine(_name + "票:");
        return price * (decimal)_discount;
    }
}

/// <summary>
/// 算法策略接口
/// </summary>
public interface IStrategy
{

    decimal Calculate(decimal price);
}

public class AppService
{
    private decimal _price;
    private readonly IStrategy _strategy;
    public AppService(IStrategy strategy)
    {
        _strategy = strategy;
    }

    public decimal Price
    {
        get => _strategy.Calculate(_price);
        set => _price = value;
    }

}