工厂模式主要是对对象的创建进行控制。
一、简单工厂模式：
根据条件取工厂类
二、工厂方法：定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法使一个类的实例化延迟到其子类。

public class test : MonoBehaviour
{

    // Use this for initialization
    void Awake()
    {
        IFactory operFactory = new AddFactory();
        Operation oper = operFactory.CreateOperation();
        oper.a = 5;
        oper.b = 2;
        var result = oper.GetResult();

        Debug.Log(result);
    }

}

abstract class Operation
{
    public double a;
    public double b;
    public abstract double GetResult();

}

class OperationAdd : Operation
{
    public override double GetResult()
    {
        return a + b;
    }
}

class OperationSub : Operation
{
    public override double GetResult()
    {
        return a - b;
    }
}

class OperationMul : Operation
{
    public override double GetResult()
    {
        return a * b;
    }
}

class OperationDiv : Operation
{
    public override double GetResult()
    {
        return a / b;
    }
}


interface IFactory
{
    Operation CreateOperation();
}

class AddFactory : IFactory
{
    public Operation CreateOperation()
    {
        return new OperationAdd();
    }
}

class SubFactory : IFactory
{
    public Operation CreateOperation()
    {
        return new OperationSub();
    }
}

class MulFactory : IFactory
{
    public Operation CreateOperation()
    {
        return new OperationMul();
    }
}

class DivFactory : IFactory
{
    public Operation CreateOperation()
    {
        return new OperationDiv();
    }
}

三、抽象工厂模式：类似抽象工厂方法，提供一个创建一系列相关或相互依赖对象的接口，无需指定具体的类。