Effective Objective-C 2.0：移动应用开发指南

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"Effective Objective-C 2.0 PDF" 是一本由 Matt Galloway 编写的专注于提升Objective-C编程技能的书籍，属于"Effective Software Development"丛书中的一本。本书由Addison Wesley Educational Publishers Inc在2013年5月16日出版，全书共320页，以英语撰写。作者Matt Galloway是一位专注于移动应用开发的软件工程师，他在英国剑桥大学学习工程，并于2007年毕业，专攻电气和信息科学。他还拥有自己的咨询公司Swipe Stack Ltd，并在Stack Overflow上解答关于Objective-C、iOS和Mac编程的问题。本书内容涵盖了Objective-C 2.0的关键概念和最佳实践，旨在帮助开发者编写更高效、更可靠的代码。虽然提供的内容没有直接列出，但根据书名可以推测，书中可能包括了如下的知识点： 1. **Objective-C基础**：包括对象模型、消息传递机制、类别（Category）、协议（Protocol）以及动态性等。 2. **内存管理**：讲解ARC（Automatic Reference Counting）的工作原理，以及如何避免内存泄漏和意外的引用计数问题。 3. **Blocks和GCD**：介绍Objective-C中的Block语法，以及如何利用Grand Central Dispatch进行并行处理。 4. **设计模式**：探讨面向对象设计模式在Objective-C中的应用，如单例（Singleton）、工厂方法（Factory Method）和代理模式（Delegate）。 5. **KVC与KVO**：深入理解Key-Value Coding和Key-Value Observing，用于动态属性访问和监听。 6. **Objective-C与Cocoa Touch框架**：讲解如何有效地使用UIKit和Cocoa Touch框架来构建iOS应用。 7. **性能优化**：提供关于提高代码性能的技巧，包括减少计算量、优化循环和使用惰性加载等。 8. **错误处理**：讨论如何正确地处理异常和错误，以及使用NSException的最佳实践。 9. **测试与调试**：介绍单元测试、集成测试以及Xcode调试工具的使用。 10. **代码组织与重构**：强调良好的代码结构和重构策略，以保持代码的可读性和可维护性。由于书籍是ePub格式，读者可以根据个人设备和应用程序的特性调整显示设置，如字体、字号、单双列布局、横竖屏模式，甚至可以点击或触摸缩放图片。对于包含编程代码或配置示例的部分，建议在单列、横屏模式下查看，并调整字体至最小，以优化代码的展示。某些情况下，代码可能以可流动文本格式显示，但也可以通过点击特定链接查看与印刷版一致的代码图像。 "Effective Objective-C 2.0"是一本针对Objective-C开发者深入学习和提升编程能力的重要资源，它涵盖了语言的核心特性、最佳实践以及如何在实际项目中应用这些知识。

1. Accustoming Yourself to Objective-C

Objective-C brings object-oriented features to C through an entirely new syntax.

Often described as verbose, Objective-C syntax makes use of a lot of square brackets

and isn’t shy about using extremely long method names. The resulting source code is

very readable but is often difficult for C++ or Java developers to master.

Writing Objective-C can be learned quickly but has many intricacies to be aware of

and features that are often overlooked. Similarly, some features are abused or not fully

understood, yielding code that is difficult to maintain or to debug. This chapter covers

fundamental topics; subsequent chapters cover specific areas of the language and

associated frameworks.

Item 1: Familiarize Yourself with Objective-C’s Roots

Objective-C is similar to other object-oriented languages, such as C++ and Java, but

also differs in many ways. If you have experience in another object-oriented language,

you’ll understand many of the paradigms and patterns used. However, the syntax may

appear alien because it uses a messaging structure rather than function calling.

Objective-C evolved from Smalltalk, the origin of messaging. The difference between

messaging and function calling looks like this:

// Messaging (Objective-C)

Object *obj = [Object new];

[obj performWith:parameter1 and:parameter2];

// Function calling (C++)

Object *obj = new Object;

obj->perform(parameter1, parameter2);

The key difference is that in the messaging structure, the runtime decides which

code gets executed. With function calling, the compiler decides which code will be

executed. When polymorphism is introduced to the function-calling example, a form of

runtime lookup is involved through what is known as a virtual table. But with messaging,

the lookup is always at runtime. In fact, the compiler doesn’t even care about the type of

the object being messaged. That is looked up at runtime as well, through a process

known as dynamic binding, covered in more detail in Item 11.

The Objective-C runtime component, rather than the compiler, does most of the

heavy lifting. The runtime contains all the data structures and functions that are

required for the object-oriented features of Objective-C to work. For example, the

runtime includes all the memory-management methods. Essentially, the runtime is the

set of code that glues together all your code and comes in the form of a dynamic library

to which your code is linked. Thus, whenever the runtime is updated, your application

benefits from the performance improvements. A language that does more work at

compile time needs to be recompiled to benefit from such performance improvements.

Objective-C is a superset of C, so all the features in the C language are available

when writing Objective-C. Therefore, to write effective Objective-C, you need to

understand the core concepts of both C and Objective-C. In particular, understanding

the memory model of C will help you to understand the memory model of Objective-C

and why reference counting works the way it does. This involves understanding that a

pointer is used to denote an object in Objective-C. When you declare a variable that is

to hold a reference to an object, the syntax looks like this:

NSString *someString = @"The string";

This syntax, mostly lifted straight from C, declares a variable called someString whose

type is NSString*. This means that it is a pointer to an NSString. All Objective-C objects

must be declared in this way because the memory for objects is always allocated in

heap space and never on the stack. It is illegal to declare a stack-allocated Objective-C

object:

NSString stackString;

// error: interface type cannot be statically allocated

The someString variable points to some memory, allocated in the heap, containing an

NSString object. This means that creating another variable pointing to the same location

does not create a copy but rather yields two variables pointing to the same object:

NSString *someString = @"The string";

NSString *anotherString = someString;

There is only one NSString instance here, but two variables are pointing to the same

instance. These two variables are of type NSString*, meaning that the current stack

frame has allocated 2 bits of memory the size of a pointer (4 bytes for a 32-bit

architecture, 8 bytes for a 64-bit architecture). These bits of memory will contain the

same value: the memory address of the NSString instance.

Figure 1.1 illustrates this layout. The data stored for the NSString instance includes

the bytes needed to represent the actual string.

heap memory. When nonobject types (int, float, double, char, etc.) are the only data to

be held, a structure, such as CGRect, is usually used.

Before embarking on writing anything in Objective-C, I encourage you to read texts

about the C language and become familiar with the syntax. If you dive straight into

Objective-C, you may find certain parts of the syntax confusing.

Things to Remember

Objective-C is a superset of C, adding object-oriented features. Objective-C uses a

messaging structure with dynamic binding, meaning that the type of an object is

discovered at runtime. The runtime, rather than the compiler, works out what code to

run for a given message.

Understanding the core concepts of C will help you write effective Objective-C. In

particular, you need to understand the memory model and pointers.

Item 2: Minimize Importing Headers in Headers

Objective-C, just like C and C++, makes use of header files and implementation files.

When a class is written in Objective-C, the standard approach is to create one of each

of these files named after the class, suffixed with .h for the header file and .m for the

implementation file. When you create a class, it might end up looking like this:

// EOCPerson.h

#import <Foundation/Foundation.h>

@interface EOCPerson : NSObject

@property (nonatomic, copy) NSString *firstName;

@property (nonatomic, copy) NSString *lastName;

@end

// EOCPerson.m

#import "EOCPerson.h"

@implementation EOCPerson

// Implementation of methods

@end

The importing of Foundation.h is required pretty much for all classes you will ever

make in Objective-C. Either that, or you will import the base header file for the

framework in which the class’s superclass lives. For example, if you were creating an

iOS application, you would subclass UIViewController often. These classes’ header

files will import UIKit.h.

As it stands, this class is fine. It imports the entirety of Foundation, but that doesn’t

matter. Given that this class inherits from a class that’s part of Foundation, it’s likely that

a large proportion of it will be used by consumers of EOCPerson. The same goes for a

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