精通Android数据库编程

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"Android.Database.Programming" 本书《Android Database Programming》由Jason Wei撰写，旨在帮助读者掌握数据驱动的Android应用开发技术。通过实践教程的方式，读者将深入理解如何在Android平台上利用数据库来创建功能丰富的应用程序。 Android数据库编程的核心是SQLite，它是Android系统内置的关系型数据库管理系统。SQLite支持SQL语法，使得开发者可以进行数据存储、查询和管理。在Android应用中，通常使用SQLiteOpenHelper这个辅助类来创建、升级和打开数据库。这个类提供了版本管理和数据库操作的基本框架。在Android中，数据存储有多种方式，包括SQLite数据库、Shared Preferences（用于存储轻量级偏好设置）、内部存储（私有的文件系统存储）和外部存储（公共文件系统存储）。然而，对于需要复杂查询和结构化数据管理的应用，SQLite通常是首选。 Android的ContentProvider组件是数据共享的关键，它允许不同应用之间访问和操作同一数据源。开发者可以通过实现ContentProvider来暴露数据库中的数据，其他应用则可以通过ContentResolver进行查询、插入、更新或删除操作。本书可能涵盖了以下关键知识点： 1. 数据库设计：介绍如何创建数据库模式，包括表的定义、字段类型选择以及主键和外键的使用。 2. CRUD操作：详细讲解如何执行创建（Create）、读取（Read）、更新（Update）和删除（Delete）数据的基本操作。 3. SQL查询：学习如何编写SQL语句，包括SELECT、INSERT、UPDATE和DELETE，以及更复杂的JOIN和子查询。 4. Cursor对象：理解如何使用Cursor遍历查询结果，并将其转化为Java对象。 5. Asynchronous查询：讨论如何在Android应用中安全地进行异步数据库操作，避免UI线程阻塞。 6. 数据库事务：介绍如何使用SQLite的事务机制确保数据的一致性和完整性。 7. 数据备份与恢复：学习如何在Android应用中实现数据库的备份和恢复功能。 8. Room Persistence Library：这是Google提供的一个高级抽象层，简化了SQLite的使用，提供了类型安全的API和编译时验证。 9. LiveData和ViewModel：这两个是Android Jetpack组件，可以帮助开发者更好地处理数据在Activity或Fragment之间的生命周期问题。 10. 性能优化：讨论如何优化数据库查询性能，如创建索引、批量操作等。通过学习这些内容，读者将能够构建出高效、稳定且数据驱动的Android应用。书中可能还包含了一些实际项目案例，以便读者将所学知识付诸实践。

Preface

[ 5 ]

Errata

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Chapter 1

[ 9 ]

Here the rst argument simply species which shared preference mapping you

want (each application can own several separate shared preference mappings, and

so, just like you would specify the table name in a database, you must specify which

mapping you want to retrieve). The second argument is a little more complex — in

the example above, we pass in MODE_PRIVATE as the argument and this argument

simply species the visibility of the shared preference instance you are retrieving

(in this case the visibility is set to private, so that only your application can access

the mappings contents). Other modes include:

•

MODE_WORLD_READABLE: Makes the visibility of your map accessible by other

applications, though contents can only be read

•

MODE_WORD_WRITEABLE: Makes the visibility of your map accessible by other

applications for both reading and writing

•

MODE_MULTI_PROCESS: This mode, available since API Level 11, allows you

to modify your map by multiple processes which may be writing to the same

shared preference instance

Now, once we have our shared preference object, we can immediately start

retrieving contents by its various

get() methods — for instance, the getString()

and getBoolean() methods we saw earlier. These get() methods will typically take

two parameters: the rst being the key, and the second being the default value if the

given key is not found. Taking the previous example, we have:

String stringValue = sp.getString("strKey", "error");

boolean booleanValue = sp.getBoolean("boolKey", false);

And so, in the rst case, we're trying to retrieve the string value associated with the

key strKey, and defaulting to the string error if no such key is found. Likewise,

in the second case, we're trying to retrieve a boolean value associated with the key

boolKey, and defaulting to the boolean false if no such key is found.

However, if you want to edit contents or add new content, then you'll have to retrieve

the

Editor object that each shared preference instance contains. This Editor object

contains all of the put() methods which allow you to pass a key along with its

associated value (just like you would for a standard Map object) — the only caveat is

that after you add or update the content of your shared preference, you need to call

the Editor object's commit() method to save down those changes. Furthermore, again,

just like a standard Map object, the Editor class also contains remove() and clear()

methods for you to freely manipulate the contents of your shared preference.

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