这是工厂方法创建模式吗？[英] Is this Factory Method creation pattern?

问题描述

I have been using factory method creation pattern for awhile now. I was just recently told that this:

public static class ScheduleTypeFactory
{
    public static IScheduleItem GetScheduleItem(ScheduleTypeEnum scheduleType)
    {
        IScheduleItem scheduleItem = null;

        switch (scheduleType)
        {
            case ScheduleTypeEnum.CableOnDemandScheduleTypeID:
                {
                    scheduleItem = new VODScheduleItem();
                    break;
                }
            case ScheduleTypeEnum.BroadbandScheduleTypeID:
                {
                    scheduleItem = new VODScheduleItem();
                    break;
                }
            case ScheduleTypeEnum.LinearCableScheduleTypeID:
                {
                    scheduleItem = new LinearScheduleItem();
                    break;
                }
            case ScheduleTypeEnum.MobileLinearScheduleTypeID:
                {
                    scheduleItem = new LinearScheduleItem();
                    break;
                }
        }

        return scheduleItem;
    }
}

is not a factory method creation pattern by my "Tech" lead without telling me why or giving me her interpretation. I kindly asked for an explanation and she told me she didn't have time. I was told to just rename it. If I am wrong, then I will no doubt accept that I have implemented this incorrectly for years. Is this how YOU would implement the factory method creation pattern? Thanks in advance.

推荐答案

I would agree to call the method a "Factory Method", though the design is not strictly a "Factory Method Pattern".
Here is a key point (from Wikipedia):

...The Factory method lets a class defer instantiation to subclasses."

Since your class is static and method static (hence non-virtual), there is no "deferring" possible.

Conceptually, notice also, that this implementation, though provides encapsulation, does not decouple/delay any decision.

Having said that, same Wikipedia article does present this schema as a variant of the "Factory Method Pattern".

Summary of the Summary: In my opinion this snippet is not a proper implementation of the "Factory Method OO Design Pattern", since it does not satisfy "a class defer instantiation to subclasses." Though, personally I would freely refer to this solution as "factory method".

To make it real factory method pattern, you need to allow the method to be overridden by subclasses. I.e. factory class (ScheduleTypeFactory) needs to be extensible (i.e. non-static), and GetScheduleItem needs to be virtual.