精通Objective-C的iPhone开发：深入Core Data与更多主题

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"More iPhone Development with Objective-C (Apress, 3rd ed, 2015)" 是一本面向已有iOS编程经验的开发者提升技能的书籍，是《Beginning iPhone Development with Objective-C》的理想后续读物。书中重点介绍了苹果持久化标准——Core Data，并详细讲解了每个Core Data概念，为编写大型应用提供了具体技巧和建议。此外，本书还涵盖了Multipeer Connectivity（蓝牙/WiFi的简单点对点模型）、MapKit、媒体库访问和播放、Interface Builder、Live Previews、自定义控件以及高级调试技术等内容，帮助开发者利用新功能更新应用程序。本书由David Mark、Jayant Varma、Jeff LaMarche、Alex Horovitz和Kevin Kim共同撰写，包含13个章节，深入探讨了以下知识点： 1. **Core Data**：解释了Core Data是什么、为什么使用以及如何使用，引导读者掌握数据管理的核心概念。 2. **添加、显示和删除数据**：在第三章中，讨论如何在应用中添加、展示和删除数据，这是构建任何数据驱动应用的基础。 3. **详细视图**：第四章探讨了如何在应用中创建详细的用户界面，以显示和编辑数据。 4. **数据迁移和版本管理**：第五章涉及数据模型的变化，包括如何处理数据迁移和版本控制，确保更新应用时数据的一致性。 5. **自定义管理对象**：第六章教授如何根据项目需求定制和扩展Core Data的管理对象。 6. **关系、属性和表达式**：第七章讲解了如何利用Core Data的实体间关系、计算属性和表达式来构建更复杂的数据模型。 7. **iCloud支持**：第八章讨论了将Core Data与iCloud集成，实现跨设备的数据同步。 8. **Multipeer Connectivity**：第九章介绍了使用蓝牙和Wi-Fi进行点对点通信的技术，让应用可以与其他设备交互。 9. **MapKit**：第十章涵盖了Apple的MapKit框架，使开发者能够集成地图和定位服务到自己的应用中。 10. **邮件、社交和iMessage**：第十一章讨论了如何实现邮件发送、社交媒体分享和iMessage集成。 11. **媒体库访问和播放**：第十二章涵盖了如何访问用户的媒体库并播放多媒体内容。 12. **自定义控件和界面设计**：通过Interface Builder和Live Previews，开发者可以创建更直观、更吸引人的用户界面。 13. **高级调试技术**：书中还包括了帮助开发者找出和修复代码问题的高级调试策略。这本书不仅适合已经有一定iOS开发基础的程序员，也适合想要深入学习Core Data和其他高级特性的开发者。通过这些详细讲解和实用示例，读者能够提升其iOS应用开发技能，充分利用Objective-C和最新iOS平台的功能。

12 CHAPTER 2: Core Data: What, Why, and How

Build and run the application. Either tap the Run button on the toolbar or select Product

➤ Run. The simulator should appear. Tap the Add (+) button in the upper right. A new row

will insert into the table that shows the exact date and time the Add button was tapped

(Figure 2-6). You can also use the Edit button to delete rows. Exciting, huh?

Figure 2-6. CoreDataApp in action

Under the hood of this simple application a lot is happening. Think about it: without adding

a single class or any code to persist data to a file or interact with a database, touching the

Add button created an object, populated it with data, and saved it to a SQLite database

created for you automatically. There’s plenty of free functionality here.

Now that you’ve seen an application in action, let’s take a look at what’s going on behind

the scenes.

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13CHAPTER 2: Core Data: What, Why, and How

Core Data Concepts and Terminology

Like most complex technologies, Core Data has its own terminology that can be a bit

confusing to newcomers. Let’s break down the mystery and get your arms around Core

Data’s nomenclature.

Figure 2-7 shows a simplified, high-level diagram of the Core Data architecture. Don’t expect

it all to make sense now, but as you look at different pieces, you might want to refer to this

diagram to cement your understanding of how they fit together.

There are five key concepts to focus on here. As you proceed through this chapter, make

sure you understand each of the following:

Data model

Persistent store

Persistent store coordinator

Managed object and managed object context

Fetch request

Once again, don’t let the names throw you. Follow along and you’ll see how all these pieces

fit together.

The Data Model

What is a data model? In an abstract sense, it’s an attempt to define the organization of data

and the relationship between the organized data components. In Core Data, the data model

defines the data structure of objects, the organization of those objects, the relationships

between those objects, and the behavior of those objects. Xcode allows you, via the model

editor and Inspector, to specify your data model for use in your application.

If you expand the CoreDataApp group in the Navigator content pane, you’ll see a file

called CoreDataApp.xcdatamodel. This file is the default data model for your project. Xcode

created this file for you because you selected the Use Core Data check box in the Project

Configuration sheet. Single-click CoreDataApp.xcdatamodel to bring up Xcode’s model editor.

Make sure the Utility pane is visible (it should be the third button on the View bar), and select

the Inspector. Your Xcode window should look like Figure 2-8.

Figure 2-7. The Core Data architecture

Data Model

Fetch Request

Persistent

Store

Persistent Store

Coordinator

Entity

Description

Managed

Objects

Managed Objects Context

based on Retrieves

Predicates

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16 CHAPTER 2: Core Data: What, Why, and How

When you select an entity in the Top-Level Components pane, the Detail editor will display,

in table style, three tables: Attributes, Relationships, and Fetched Properties. Again, we’ll

cover these in detail in a little bit. You can add a new attribute by using the Add Attribute

button below the Detail editor. Similar to the Add Entity button, clicking and holding will

reveal a pop-up menu of choices: Add Attribute, Add Relationship, and Add Fetched

Property. Again, the single-click behavior of this button will change depending on your

choice, with its label reflecting that behavior. Under the Editor menu there are three menu

items: Add Attribute, Add Relationship, and Add Fetched Property. These are active only

when an entity is selected in the Top-Level Components pane.

If you switch the Detail editor to graph style, you’ll see a large grid with a single rounded

rectangle in the center. This rounded rectangle represents the entity in the Top-Level

Components pane. The template you used for this project creates a single entity, Event.

Selecting Event in the Top Level Components pane is the same as selecting the rounded

rectangle in the graph view.

Try it. Click outside the entity in the Detail editor grid to deselect it and then click the Event

line in the Top-Level Components pane. The entity in the graph view will also be selected.

The Top Level Components pane and the graph view show two different views of the same

entity list.

When unselected, the title bar and lines of the Event entity square should be pink. If you

select the Event entity in the Top-Level Components pane, the Event entity in the Detail

editor should change color to blue, indicating it’s selected. Now click anywhere on the Detail

editor grid, outside the Event rounded square. The Event entity should be deselected in

the Top Level Components pane and should change color in the Detail editor. If you click

the Event entity in the Detail editor, it will be selected again. When selected, the Event entity

should have a resize handle (or dot) on the left and right sides, allowing you to resize its width.

You are currently given the Event entity. It has a single attribute, named timeStamp, and

no relationships. The Event entity was created as part of this template. As you design your

own data models, you’ll most likely delete the Event entity and create your own entities from

scratch. A moment ago, you ran your Core Data sample application in the simulator. When

you clicked the + icon, a new instance of Event was created. Entities, which we’ll look at

more closely in a few pages, replace the Objective-C data model class you would otherwise

use to hold your data. We’ll get back to the model editor in just a minute to see how it works.

For now, just remember that the persistent store is where Core Data stores its data, and the

data model defines the form of that data. Also remember that every persistent store has one,

and only one, data model.

The inspector provides greater detail for the items selected in the model editor. Since each

item could have a different view in the inspector, we’ll discuss the details as we discuss

the components and their properties. That being said, let’s discuss the three top-level

components: entities, fetch requests, and configurations.

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