public class Customer
{
    public void CallSomeOne(){
        PhoneA p1 = new PhoneA();
        p1.Call();
    }
}
public class PhoneA
{
    public void Call(){}
}
public class PhoneB
{
    public void Call(){}
}

using System;
namespace Example1
{
    public interface IProduct { }
    public class PhoneA : IProduct { }
    public class PhoneB : IProduct { }
    public class Factory
    {
        public IProduct Create()
        {
            // 工廠決定到底實例化哪個子類。
            return new PhonetA ();
        }
    }
}
using System;
namespace Example1
{
    public enum Category
    {
        A,

    }
    public static class ProductFactory
    {
        public static IProduct Create(Category category)
        {
            switch (category)
            {
                case Category.A:
                    return new PhoneA();
                case Category.B:
                    return new PhoneB();
                default:
                    throw new NotSupportedException();
            }
        }
    }
}

[TestMethod]
        public void Test()
        {
            Factory factory = new Factory();
            IProduct phone = factory.Create();   
            Assert.AreEqual<Type>(phone.GetType(), typeof(PhoneA));
        }

namespace Example2
{
    /// <summary>
    /// 抽象的工廠類型特性描述
    /// </summary>
    public interface IFactory
    {
        IProduct Create();  //  每個工廠所需要具有的工廠方法――創建產品
    }
    /// <summary>
    /// 實體工廠類型
    /// </summary>
    public class FactoryA : IFactory
    {
        public IProduct Create()
        {
            return new PhoneA();
        }
    }
    /// <summary>
    /// 實體工廠類型
    /// </summary>
    public class FactoryB : IFactory
    {
        public IProduct Create()
        {
            return new PhoneB();
        }
    }
}
using System;
using System.Diagnostics;
namespace Example2
{
    class Client
    {
        public void SomeMethod()
        {
            IFactory factory = new FactoryA();   // 獲得了抽象Factory的同時，與FactoryA產生依賴；
            IProduct Phone = factory.Create(); // 后續操作僅以來抽象的IFactory和IProduct完成
            // ...
        }
        private IFactory factory;
        public Client(IFactory factory)     // 將IFactory通過Setter方式注入
        {
            if (factory == null) throw new ArgumentNullException("factory");
            this.factory = factory;
        }
        public void AnotherMethod()
        {
            IProduct Phone = factory.Create();
            // ... ...
        }
    }
}