工厂模式 Factory Pattern

简述：由工厂类决定实例化哪种实例，延迟创建过程，主要解决接口选择的问题。

Step1: 实现一个interface ICar

using System.Xml.Serialization;

namespace LearnDesignPatterns.Patterns.FactoryPattern
{
    public interface ICar
    {
        public string GetName();
    }
}

Step2: 实现ICar接口的实体类

namespace LearnDesignPatterns.Patterns.FactoryPattern
{
    public class BMW420i : ICar
    {
        public string Name
        {
            get => "BMW 420i";
        }
        public string GetName()
        {
            return Name;
        }
    }
    
    public class TeslaModel3 : ICar
    {
        public string Name
        {
            get => "Tesla Model III";
        }
        public string GetName()
        {
            return Name;
        }
    }
}

Step3: 创建工厂

namespace LearnDesignPatterns.Patterns.FactoryPattern
{
    public class CarFactory
    {
        public ICar GetCar(string carType)
        {
            return carType switch
            {
                "BMW" => (ICar) new BMW420i(),
                "TESLA" => new TeslaModel3(),
                _ => null
            };
        }
    }
}

Step4: 执行&Log

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection.Metadata.Ecma335;

namespace LearnDesignPatterns.Patterns.FactoryPattern
{
    public class FactoryPatternExecutor : IExecutor
    {
        public void Execute()
        {
            var carFactory = new CarFactory();
            var cars = new List<ICar>()
            {
                carFactory.GetCar("BMW"),
                carFactory.GetCar("TESLA"),
                carFactory.GetCar("TOYOTA")
            };
            foreach (var s in cars) Log(s);
        }
        private static void Log(ICar car)
        {
            Console.WriteLine(car == null
                ? $"[Car Factory Info] This car product failed"
                : $"[Car Factory Info] This car is {car.GetName()}");
        }
    }
}

Output:

/usr/local/share/dotnet/dotnet /Users/garry/RiderProjects/LearnDesignPatterns/LearnDesignPatterns/bin/Debug/netcoreapp3.1/LearnDesignPatterns.dll
[Car Factory Info] This car is BMW 420i
[Car Factory Info] This car is Tesla Model III
[Car Factory Info] This car product failed

Process finished with exit code 0.

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