Objective-C：何时知道你在滥用全局变量的SIngleton方法 [英] Objective-C: When to know that you are abusing the SIngleton method of Global Variables

问题描述

因此，我的客户iPhone应用程序在过去的几周里已经从5个左右的班级放到了25个以上。有了这么大的（对于iPhone来说）类结构，我一直在使用Singleton类来访问全局变量。问题是，无论何时我需要访问我正在处理的类之外的变量，我都可以选择修改代码以将引用传递给变量，或者将其引入单例中。当然，将它扔到单身人士中的代码和努力要少很多，但是现在单身人士似乎开始看起来像不相干的全局变量。

我的问题是，如何维护一个具有不相关全局变量的大型单例对象，以及通常是最佳实践非平凡的iphone应用程序？

非常感谢您的建议！

解决方案

在解耦设计的上下文中对此问题进行了详细分析 。我会尽量总结我的观点：

1. 如果您的Singleton具有显着的全局状态，请不要使用Singleton。这包括持久性存储，如数据库，文件等。


2. 在类名不依赖单例对象的情况下，应该注入依赖关系。将Singleton实例注入类的需求证明了该模式的错误用法（请参见第1点）。


3. 假设Singleton的生命周期与应用程序的生命周期相同。大多数Singleton实现都使用延迟加载机制来实例化自己。这是微不足道的，它们的生命周期不太可能改变，否则你不应该使用Singleton。

So my clients iphone app has balloned from 5 or so classes to over 25 in the last few weeks. With such a large (for the iphone anyway) class structure I've been utilizing the Singleton class for accessing global variables. The problem is that whenever I need to access a variable outside of the class I'm working on, I have a choice of either modifying the code to pass a reference to the variable or just throw it in the singleton. Of course throwing it in the singleton is a lot less code and effort, however, now the singleton is beginning to look like a mish-mosh of unrelated globals.

My question is how appropriate is it to maintain a large singleton object with unrelated global vars and what is generally the "best practice" way of sharing data across classes in a "non-trivial" iphone app?

Many thanks in advance for your advice!

解决方案

I have done a detailed analysis of this problem in the context of a decoupled design. I'll try to summarize my points:

1. If your Singleton carries a significant global state, don’t use Singleton. This includes persistent storage such as Databases, Files etc.
2. In cases, where dependency on a Singleton Object is not obvious by the classes name, the dependency should be injected. The need to inject Singleton Instances into classes proves a wrong usage of the pattern (see point 1).
3. A Singleton’s life-cycle is assumed to be the same as the application’s. Most Singleton implementations are using a lazy-load mechanism to instantiate themselves. This is trivial and their life-cycle is unlikely to change, or else you shouldn’t use Singleton.

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