深入解析iOS应用架构

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"Advanced_iOS_App_Architec.pdf 是一本深入探讨iOS应用程序架构的书籍，由René Cacheaux和Josh Berlin合著。该书旨在详细介绍并演示如何逐一应用流行的iOS应用架构。" 本书主要围绕Swift编程语言和Apple的iOS平台，深入讲解了多种iOS应用架构，对于想要提升iOS开发技能的开发者来说是一份宝贵的资源。标签中的"Swift"、"ios"、"Apple"和"Programming"框架，表明内容将涵盖与这些主题紧密相关的技术知识。虽然部分内容没有提供具体的架构细节，但我们可以推测书中可能涉及以下常见的iOS应用架构模式： 1. **Model-View-Controller (MVC)**：这是iOS开发中最基础的架构模式，将应用程序分为模型、视图和控制器三个部分，每个部分都有明确的责任划分。 2. **Model-View-ViewModel (MVVM)**：在MVVM架构中，视图模型作为视图和模型之间的桥梁，负责数据转换和业务逻辑，使视图层更专注于显示。 3. **VIPER (View-Interactor-Presenter-Entity-Router)**：这是一种模块化的架构，将应用程序拆分为多个小的、可测试的部分，提高了代码的可维护性。 4. **Clean Architecture**：这种架构强调解耦，通过定义清晰的边界，将业务逻辑、数据访问和用户界面分离。 5. **Unidirectional Data Flow (如Redux or Flux)**：这些架构模式促进了数据在一个单一方向上的流动，通常用于状态管理，使得状态变更更为可控。 6. **Functional Reactive Programming (FRP)**：FRP是一种编程范式，利用函数式编程和反应式编程的特性，处理异步事件流和数据流。 7. **Protocol-Oriented Programming (POP)**：Swift的一个重要特性，POP强调使用协议来组合和扩展功能，而不是继承，使得代码更加灵活和可扩展。 8. **SOLID原则**：这是一组设计原则，包括单一职责、开放封闭、里氏替换、接口隔离和依赖倒置，指导开发者编写可维护和可扩展的代码。在阅读这本书的过程中，读者不仅会了解到各种架构的优缺点，还会学习到如何根据项目需求选择合适的架构，以及如何有效地组织和测试代码。此外，书中可能还涵盖了如何逐步迁移现有的代码库至新架构，以及如何解决架构升级过程中可能出现的问题。最后，书中的"Notice of Rights"和"Notice of Liability"章节提醒读者尊重版权，并指出内容的使用应遵循一定的法律条款，同时明确了作者和版权所有者不对软件使用中可能产生的任何损害负责。 "Advanced iOS App Architecture"是一本面向中级到高级iOS开发者的专业书籍，它将帮助开发者深入了解和掌握构建高质量iOS应用的各种架构策略。

Chapter 2: Which

Architecture Is Right for Me?

By René Cacheaux

You might be wondering: Which architecture pattern is right for me? Honestly, there's

no perfect universal app architecture. An architecture that works best for one project

might not work best for your project. There are many different aspects to consider

when establishing an architecture for you and your team to follow. This chapter guides

you through the process of finding the best architecture for your project.

There's a lot that goes into shaping your app's codebase into a cohesive and effective

architecture. Knowing where to start can especially be overwhelming. Every single file

in your app's codebase plays a part in your app's architecture. There's no shortage of

architecture patterns. Unfortunately, most patterns only scratch the surface and leave

you to figure out the fine details. In addition, many patterns are similar to one another

and have only minor differences here and there.

All of this makes architecture hard to put into practice. Fortunately, there are pragmatic

steps you can take to ensure your architecture is effective:

1. Understand the current state of your codebase.

2. Identify problems you'd like to solve or code you'd like to improve.

3. Evaluate different architecture patterns.

4. Try a couple patterns on for size before committing to one.

5. Draw a line in the sand and define your app's baseline architecture.

6. Look back and determine if your architecture is effectively addressing the problems

you want to solve.

7. Iterate and evolve your app’s architecture over time.

raywenderlich.com

Notice how selecting an architecture pattern isn't the first item on the list. The reality

is that selecting an architecture pattern is less important than understanding the the

problems you're trying to solve using architectural patterns. Taking the time to

understand the problems you want to solve allows you to focus on the few aspects of

architecture that really make a difference. While many problems will be specific to your

project, there are several general problems you can solve through good architecture.

The next several sections cover these general problems in detail.

Identifying problems to solve

Before embarking on any architecture project, you should first identify and understand

the problems you'd like to solve. This will allow you to evaluate whether you're getting

the most out of your app's architecture. A good architecture enables you and your team

to easily and safely change code without a ton of risk. Making changes to code in a

codebase that is not architected well is expensive and risky. The two primary problems

that good architecture practices solve are slow team velocity and fragile code

quality. Additionally, good architecture practices can help you prevent rigid software.

The next sections cover these two primary problems followed by a section that covers

rigid software.

Boosting team velocity and

strengthening code quality

A good app architecture enables you to deliver features and bug fixes faster without

compromising on quality. On the other hand, a less-than-ideal architecture slows your

team down and makes your codebase very difficult to change without breaking existing

functionality. Knowing this, what problems should you be looking for? Which problems

can architecture solve? Here are several problems that, when present, lead to slow

velocity and fragile code quality:

• My app's codebase is hard to understand.

• Changing my app's codebase sometimes causes regressions.

• My app exhibits fragile behavior when running.

• My code is hard to re-use.

• Changes require large code refactors.

Advanced iOS App Architecture Chapter 2: Which Architecture Is Right for Me?

raywenderlich.com

Adding code to an existing type is much easier than coming up with a new type. When

creating a new type, you have to think about so many things: What should the type be

responsible for? How long should instances of this type live for? Should any existing

code be moved to this type? What if this new type needs access to state held by another

type?

Designing object-oriented systems takes time. When you're under pressure to deliver a

feature making this tradeoff can be difficult. The opportunity cost is hard to see. The

thing is, many problems are caused by large types – problems that will slow you down

and problems that will affect your code's quality. You'll read about examples of these

consequences in the following sections. For now, just know that breaking large types

into smaller types is a great way to improve your codebase's architecture.

Now that you're familiar with the root causes, you're ready to dig into the problems that

can cause slow team velocity and fragile code quality.

Examining the problems

If you're looking to boost your team's velocity and to strengthen your code's quality,

addressing the root causes is a good start. But you might be wondering how the root

causes affect team velocity and code quality.

Note: As you read the upcoming sections, keep in mind that highly

interdependent code and large types are just the common root causes. You'll see

these common root causes in almost all the problem sections below. However,

you'll also read about other, problem-specific, root causes.

With that in mind, it's time to examine the problems associated with team velocity and

code quality.

My app's codebase is hard to understand

Have you ever spent hours trying to figure out how a view controller works? Code is

inherently difficult to understand because code is textual. The connections between

files and types are hard to see. Having a solid understanding of how parts in your

codebase are connected really helps you reason about how your code works. Therefore,

the way an app is architected plays a huge role in the ease of code readability.

Advanced iOS App Architecture Chapter 2: Which Architecture Is Right for Me?

raywenderlich.com

There are several ways in which architecture can impact readability:

How long are your class implementations?

600 line view controllers are very difficult to understand. If all you need to know is how

a button functions, fishing through 600 lines of view controller code will take a lot of

valuable time. A good architecture breaks large chunks of code into small, modular

pieces that are easy to read and understand. The more an architecture encourages

locally encapsulated behavior and state, the easier the code will be to read. Think about

the current app you're working on. If a new team member joins your team tomorrow

and needs to understand a single view controller, what percentage of the app's overall

codebase will that developer need to understand? This is a good gauge to use when

evaluating how much your architecture is helping improve your code's readability.

Unfortunately, most architecture patterns don't emphasize this point enough. The good

news is that this practice can be applied to pretty much any architecture pattern. So

this is more of a universal aspect of architecture.

How many global variables does your codebase have, and how many objects are

instantiated directly in another object?

The more your objects directly depend on each other and the more your objects depend

on global state, the less information a developer will have when reading a single file.

This makes it incredibly difficult to know how a change in a file might affect code living

in another file. This forces developers to Command-click into tons of files in order to

piece together the control flow. This takes a lot of time. Similar to class size, carefully

managing dependencies is unfortunately not emphasized enough by popular

architecture patterns. Carefully managing dependencies is a universal aspect that can

be applied to any architecture pattern. In fact, we apply this aspect to every

architecture code example that ships with this book. We also dedicated a whole chapter

to this. You can read more about managing dependencies in Chapter 4.

How differently are your view controllers implemented across your app's

codebase?

Developers, including your future self, will spend a lot of time figuring things out if

different features are implemented using different architecture patterns. Human brains

are amazing at identifying patterns. You can take advantage of this ability by ensuring

your codebase follows similar architecture patterns throughout. Having a consistent

structure drastically reduces the cognitive overhead required to understand code. In

turn, developers will feel more comfortable changing and improving older parts of an

app's codebase because they'll understand the common patterns.

Advanced iOS App Architecture Chapter 2: Which Architecture Is Right for Me?

raywenderlich.com

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