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总计105课&/b&&/h2&&p&课时1：面向对象简介 13:22&/p&&p&课时2：类与对象（类与对象基本定义） 09:38&/p&&p&课时3：类与对象（类与对象定义） 09:36&/p&&p&课时4：类与对象（对象内存分析） 20:13&/p&&p&课时5：类与对象（引用传递初次分析） 15:00&/p&&p&课时6：private实现封装处理 16:29&/p&&p&课时7：构造方法与匿名对象 23:55&/p&&p&课时8：【第01个代码模型】综合案例：简单Java类 12:53&/p&&p&课时9：数组的定义与使用（数组基本概念） 14:32&/p&&p&课时10：数组的定义与使用（数组引用传递） 10:40&/p&&p&课时11：数组的定义与使用（数组静态初始化） 06:46&/p&&p&课时12：数组的定义与使用（二维数组） 11:20&/p&&p&课时13：数组的定义与使用（数组与方法互操作） 12:42&/p&&p&课时14：数组的定义与使用（Java对数组的支持） 08:57&/p&&p&课时15：数组的定义与使用（数组案例：数组数据统计） 16:51&/p&&p&课时16：数组的定义与使用（数组案例：数组排序） 13:28&/p&&p&课时17：数组的定义与使用（数组案例：数组转置） 20:16&/p&&p&课时18：数组的定义与使用（数组案例：二分查找法） 13:14&/p&&p&课时19：数组的定义与使用（对象数组） 09:05&/p&&p&课时20：String类的基本特点（String类两种实例化方式） 04:48&/p&&p&课时21：String类的基本特点（字符串比较） 08:09&/p&&p&课时22：String类的基本特点（字符串为匿名对象） 06:33&/p&&p&课时23：String类的基本特点（String两种实例化区别） 20:37&/p&&p&课时24：String类的基本特点（字符串常量不可变更） 10:05&/p&&p&课时25：String类的常用方法（DOC文档组成） 07:18&/p&&p&课时26：String类的常用方法（字符串与字符数组） 11:41&/p&&p&课时27：String类的常用方法（字节与字符串） 05:38&/p&&p&课时28：String类的常用方法（字符串比较） 06:13&/p&&p&课时29：String类的常用方法（字符串查找） 10:57&/p&&p&课时30：String类的常用方法（字符串替换） 02:49&/p&&p&课时31：String类的常用方法（字符串拆分） 07:33&/p&&p&课时32：String类的常用方法（字符串截取） 03:07&/p&&p&课时33：String类的常用方法（字符串其它操作方法） 12:31&/p&&p&课时34：this关键字（this调用属性） 07:15&/p&&p&课时35：this关键字（this调用方法） 09:58&/p&&p&课时36：this关键字（表示当前对象） 06:02&/p&&p&课时37：引用传递进阶分析 20:54&/p&&p&课时38：【第02个代码模型】综合案例：对象比较 11:22&/p&&p&课时39：引用传递实际应用 19:12&/p&&p&课时40：【第03个代码模型】综合案例：数据表与简单Java类（一对多） 17:07&/p&&p&课时41：【第03个代码模型】综合案例：数据表与简单Java类（多对多） 20:40&/p&&p&课时42：【第03个代码模型】综合案例：数据表与简单Java类（角色与权限） 26:58&/p&&p&课时43：static关键字（static属性） 17:08&/p&&p&课时44：static关键字（static方法） 06:25&/p&&p&课时45：static关键字（分析主方法） 08:41&/p&&p&课时46：static关键字（static应用） 06:24&/p&&p&课时47：代码块（普通代码块） 04:24&/p&&p&课时48：代码块（构造块） 04:09&/p&&p&课时49：代码块（静态代码块） 05:11&/p&&p&课时50：内部类的定义及使用（内部类基本概念） 20:56&/p&&p&课时51：内部类的定义及使用（static定义内部类） 04:58&/p&&p&课时52：内部类的定义及使用（在方法中定义内部类） 07:01&/p&&p&课时53：继承的定义与使用（继承问题的引出） 06:02&/p&&p&课时54：继承的定义与使用（继承的实现） 06:25&/p&&p&课时55：继承的定义与使用（继承使用限制） 21:13&/p&&p&课时56：覆写（方法覆写） 19:36&/p&&p&课时57：覆写（属性覆盖） 03:23&/p&&p&课时58：覆写（super关键字） 09:35&/p&&p&课时59：综合案例：数组操作（定义Array父类） 18:17&/p&&p&课时60：综合案例：数组操作（SortArray排序子类） 05:15&/p&&p&课时61：综合案例：数组操作（ReverseArray反转子类） 03:48&/p&&p&课时62：final关键字 06:05&/p&&p&课时63：多态性 28:26&/p&&p&课时64：抽象类的定义与使用（抽象类基本概念） 16:39&/p&&p&课时65：抽象类的定义与使用（抽象类使用限制） 18:06&/p&&p&课时66：抽象类的定义与使用（模版设计模式） 18:58&/p&&p&课时67：接口的定义与使用（接口基本概念） 17:34&/p&&p&课时68：接口的定义与使用（接口使用限制） 22:56&/p&&p&课时69：接口的定义与使用（使用接口定义标准） 14:34&/p&&p&课时70：接口的定义与使用（工厂设计模式） 13:23&/p&&p&课时71：接口的定义与使用（代理设计模式） 14:41&/p&&p&课时72：接口的定义与使用（抽象类与接口的区别） 12:51&/p&&p&课时73：匿名内部类 09:25&/p&&p&课时74：Object类（Object类简介） 06:01&/p&&p&课时75：Object类（取得对象信息） 07:45&/p&&p&课时76：Object类（对象比较） 08:50&/p&&p&课时77：Object类（接收引用数据类型） 05:46&/p&&p&课时78：包装类（包装类简介） 09:08&/p&&p&课时79：包装类（装箱与拆箱） 09:46&/p&&p&课时80：包装类（字符串与基本数据类型转换） 10:21&/p&&p&课时81：包的定义及使用（包的定义） 10:19&/p&&p&课时82：包的定义及使用（包的导入） 13:34&/p&&p&课时83：包的定义及使用（系统常用包） 08:36&/p&&p&课时84：访问控制权限 10:45&/p&&p&课时85：jar命令 09:38&/p&&p&课时86：单例设计模式（单例设计模式） 18:04&/p&&p&课时87：单例设计模式（多例设计模式） 05:43&/p&&p&课时88：【第04个代码模型】异常的捕获与处理（观察异常带来的问题） 05:35&/p&&p&课时89：【第04个代码模型】异常的捕获与处理（异常处理格式） 15:16&/p&&p&课时90：【第04个代码模型】异常的捕获与处理（throws关键字） 08:09&/p&&p&课时91：【第04个代码模型】异常的捕获与处理（throw关键字） 06:17&/p&&p&课时92：【第04个代码模型】异常的捕获与处理（异常处理模型） 09:03&/p&&p&课时93：【第04个代码模型】异常的捕获与处理（RuntimeException） 06:43&/p&&p&课时94：【第04个代码模型】异常的捕获与处理（断言） 04:20&/p&&p&课时95：【第04个代码模型】异常的捕获与处理（自定义异常类） 05:35&/p&&p&课时96：链表（链表基本概念） 17:03&/p&&p&课时97：链表（链表实现结构说明） 11:17&/p&&p&课时98：链表（增加链表数据） 16:14&/p&&p&课时99：链表（取得链表数据个数） 04:26&/p&&p&课时100：链表（链表数据转换为对象数组） 14:08&/p&&p&课时101：链表（查询数据） 06:01&/p&&p&课时102：链表（根据索引取得数据） 05:24&/p&&p&课时103：链表（修改指定索引数据） 04:07&/p&&p&课时104：链表（删除数据） 12:18&/p&&p&课时105：【第05个代码模型】综合案例：宠物商店 19:48&/p&&h2&&a href=&//link.zhihu.com/?target=http%3A//click.aliyun.com/m/25785/& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&Java高级开发&/a&&b&（点击标题学习视频课程）
总计155课&/b&&/h2&&p&课时1：Eclipse开发工具（Eclipse简介） 18:13&/p&&p&课时2：Eclipse开发工具（使用JDT开发程序） 33:05&/p&&p&课时3：Eclipse开发工具（debug调试） 09:08&/p&&p&课时4：Eclipse开发工具（junit测试工具） 06:07&/p&&p&课时5：Java基础新特性（可变参数） 11:02&/p&&p&课时6：Java基础新特性（foreach输出） 04:43&/p&&p&课时7：Java基础新特性（静态导入） 05:38&/p&&p&课时8：泛型（泛型问题引出） 10:03&/p&&p&课时9：泛型（泛型实现） 06:55&/p&&p&课时10：泛型（通配符） 17:37&/p&&p&课时11：泛型（泛型接口） 04:48&/p&&p&课时12：泛型（泛型方法） 03:14&/p&&p&课时13：枚举（多例与枚举） 06:15&/p&&p&课时14：枚举（Enum类） 05:30&/p&&p&课时15：枚举（枚举中定义其它结构） 05:48&/p&&p&课时16：枚举（枚举应用） 05:24&/p&&p&课时17：Annotation（代码开发逻辑） 12:10&/p&&p&课时18：Annotation（准确覆写） 05:44&/p&&p&课时19：Annotation（过期声明） 04:46&/p&&p&课时20：Annotation（压制警告） 04:12&/p&&p&课时21：接口定义加强 12:14&/p&&p&课时22：Lambda表达式 15:33&/p&&p&课时23：方法引用 12:15&/p&&p&课时24：内建函数式接口 12:30&/p&&p&课时25：进程与线程 13:20&/p&&p&课时26：Java多线程实现（Thread类实现多线程） 21:34&/p&&p&课时27：Java多线程实现（Runnable接口实现多线程） 07:44&/p&&p&课时28：Java多线程实现（Thread与Runnable区别） 16:39&/p&&p&课时29：Java多线程实现（线程状态） 02:50&/p&&p&课时30：Java多线程实现（Callable实现多线程） 14:36&/p&&p&课时31：多线程常用操作方法（线程命名和取得） 13:37&/p&&p&课时32：多线程常用操作方法（线程休眠） 08:00&/p&&p&课时33：多线程常用操作方法（线程优先级） 07:25&/p&&p&课时34：线程的同步与死锁（同步问题引出） 11:09&/p&&p&课时35：线程的同步与死锁（同步处理） 11:20&/p&&p&课时36：线程的同步与死锁（死锁） 07:54&/p&&p&课时37：【第06个代码模型】综合案例：生产者与消费者（基础模型） 10:48&/p&&p&课时38：【第06个代码模型】综合案例：生产者与消费者（解决同步问题） 04:24&/p&&p&课时39：【第06个代码模型】综合案例：生产者与消费者（解决重复操作问题） 09:44&/p&&p&课时40：线程池（线程池概念） 08:30&/p&&p&课时41：线程池（线程池实现） 10:49&/p&&p&课时42：StringBuffer类 18:34&/p&&p&课时43：Runtime类 10:39&/p&&p&课时44：System类 12:04&/p&&p&课时45：对象克隆 05:48&/p&&p&课时46：【第07个代码模型】日期处理类（Date类） 06:07&/p&&p&课时47：【第07个代码模型】日期处理类（SimpleDateFormat类） 11:20&/p&&p&课时48：数字操作类（Math类） 08:48&/p&&p&课时49：数字操作类（随机数） 03:23&/p&&p&课时50：数字操作类（大数字操作类） 12:54&/p&&p&课时51：Arrays类 04:14&/p&&p&课时52：比较器（Comparable） 11:35&/p&&p&课时53：比较器（二叉树） 15:04&/p&&p&课时54：比较器（Comparator） 08:35&/p&&p&课时55：国际化程序（国际化实现原理） 09:30&/p&&p&课时56：国际化程序（Locale类） 06:58&/p&&p&课时57：国际化程序（ResourceBundle） 10:28&/p&&p&课时58：国际化程序（国际化程序实现） 07:45&/p&&p&课时59：观察者设计模式 09:21&/p&&p&课时60：定时器 07:15&/p&&p&课时61：UUID类 02:16&/p&&p&课时62：Base64加密处理 09:07&/p&&p&课时63：【第08个代码模型】ThreadLocal类 15:09&/p&&p&课时64：【第09个代码模型】正则表达式（正则问题引出） 08:59&/p&&p&课时65：【第09个代码模型】正则表达式（正则符号） 17:52&/p&&p&课时66：【第09个代码模型】正则表达式（String类对正则的支持） 27:53&/p&&p&课时67：【第09个代码模型】正则表达式（java.util.regex开发包） 10:20&/p&&p&课时68：File文件操作类（File类基本操作） 19:01&/p&&p&课时69：File文件操作类（创建目录） 06:44&/p&&p&课时70：File文件操作类（取得文件信息） 09:45&/p&&p&课时71：File文件操作类（综合案例：目录列表） 11:15&/p&&p&课时72：字节流与字符流（流操作简介） 07:07&/p&&p&课时73：字节流与字符流（字节输出流：OutputStream） 23:21&/p&&p&课时74：字节流与字符流（AutoCloseable自动关闭支持） 06:44&/p&&p&课时75：字节流与字符流（字节输入流：InputStream） 15:31&/p&&p&课时76：字节流与字符流（字符输出流：OutputStream） 04:48&/p&&p&课时77：字节流与字符流（字符输入流：Reader） 05:24&/p&&p&课时78：字节流与字符流（字节流与字符流区别） 08:35&/p&&p&课时79：转换流 10:28&/p&&p&课时80：【第10个代码模型】综合案例：文件拷贝 33:34&/p&&p&课时81：字符编码（常用字符编码） 05:55&/p&&p&课时82：字符编码（乱码产生分析） 07:17&/p&&p&课时83：内存操作流（内存流基本操作） 19:32&/p&&p&课时84：内存操作流（内存流操作） 20:36&/p&&p&课时85：【第11个代码模型】打印流（打印流模型） 10:32&/p&&p&课时86：【第11个代码模型】打印流（使用系统打印流） 11:02&/p&&p&课时87：【第11个代码模型】打印流（格式化文本信息） 06:08&/p&&p&课时88：System类对IO的支持（系统输出） 09:59&/p&&p&课时89：System类对IO的支持（系统输入） 15:58&/p&&p&课时90：BufferedReader类 12:08&/p&&p&课时91：【第12个代码模型】Scanner类 13:13&/p&&p&课时92：【第13个代码模型】对象序列化（序列化基本概念） 04:52&/p&&p&课时93：【第13个代码模型】对象序列化（序列化实现） 11:43&/p&&p&课时94：【第13个代码模型】对象序列化（transient关键字） 03:56&/p&&p&课时95：认识反射机制 06:14&/p&&p&课时96：Class类对象的三种实例化模式 09:16&/p&&p&课时97：【第14个代码模型】反射与工厂设计模式 18:09&/p&&p&课时98：反射与类操作（取得父类信息） 06:03&/p&&p&课时99：反射与类操作（反射调用构造） 19:12&/p&&p&课时100：反射与类操作（反射调用方法） 12:15&/p&&p&课时101：反射与类操作（反射调用成员） 19:45&/p&&p&课时102：【第15个代码模型】综合案例：反射与简单Java类（单级VO操作原理） 18:26&/p&&p&课时103：【第15个代码模型】综合案例：反射与简单Java类（单级VO设置实现） 28:23&/p&&p&课时104：【第15个代码模型】综合案例：反射与简单Java类（多级VO设置实现） 14:59&/p&&p&课时105：【第15个代码模型】综合案例：反射与简单Java类（设置各种数据类型） 35:56&/p&&p&课时106：【第15个代码模型】综合案例：反射与简单Java类（级联实例化对象） 06:41&/p&&p&课时107：ClassLoader类加载器（认识类加载器） 14:44&/p&&p&课时108：ClassLoader类加载器（自定义ClassLoader） 12:48&/p&&p&课时109：【第16个代码模型】反射与代理设计模式（基础代理设计模式） 19:49&/p&&p&课时110：【第16个代码模型】反射与代理设计模式（动态代理设计模式） 20:55&/p&&p&课时111：【第16个代码模型】反射与代理设计模式（cglib实现动态代理） 12:13&/p&&p&课时112：反射与Annotation（反射取得Annotation） 07:49&/p&&p&课时113：反射与Annotation（自定义Annotation） 08:47&/p&&p&课时114：反射与Annotation（Annotation与工厂设计模式） 06:43&/p&&p&课时115：volatile关键字 14:20&/p&&p&课时116：网络编程（网络编程简介） 08:15&/p&&p&课时117：网络编程（基本网络程序模型） 09:26&/p&&p&课时118：网络编程（Echo程序） 18:00&/p&&p&课时119：JDBC简介 08:12&/p&&p&课时120：连接Oracle数据库 26:06&/p&&p&课时121：使用Statement操作数据库（Statement接口简介） 09:29&/p&&p&课时122：使用Statement操作数据库（Statement执行更新操作） 09:17&/p&&p&课时123：使用Statement操作数据库（Statement执行查询操作） 12:42&/p&&p&课时124：【第17个代码模型】使用PreparedStatement操作数据库（Statement执行分析） 16:50&/p&&p&课时125：【第17个代码模型】使用PreparedStatement操作数据库（PreparedStatement查询案例） 11:42&/p&&p&课时126：批处理与事务处理（批处理） 11:11&/p&&p&课时127：批处理与事务处理（事务处理） 07:04&/p&&p&课时128：Java类集简介 05:56&/p&&p&课时129：Collection集合接口 16:09&/p&&p&课时130：【第18个代码模型】List集合接口（List接口简介） 10:17&/p&&p&课时131：【第18个代码模型】List集合接口（ArrayList子类） 07:54&/p&&p&课时132：【第18个代码模型】List集合接口（List与简单Java类） 06:05&/p&&p&课时133：【第18个代码模型】List集合接口（Vector子类） 10:09&/p&&p&课时134：【第18个代码模型】List集合接口（LinkedList子类） 11:23&/p&&p&课时135：【第19个代码模型】Set集合接口（Set接口常用子类） 09:19&/p&&p&课时136：【第19个代码模型】Set集合接口（集合排序说明） 08:55&/p&&p&课时137：【第19个代码模型】Set集合接口（重复元素判断） 13:37&/p&&p&课时138：【第20个代码模型】集合输出（Iterator迭代输出） 09:04&/p&&p&课时139：【第20个代码模型】集合输出（ListIterator双向迭代） 08:11&/p&&p&课时140：【第20个代码模型】集合输出（Enumeration枚举输出） 05:25&/p&&p&课时141：【第20个代码模型】集合输出（foreach输出） 02:52&/p&&p&课时142：【第21个代码模型】Map集合（Map接口概述） 09:31&/p&&p&课时143：【第21个代码模型】Map集合（HashMap子类） 09:36&/p&&p&课时144：【第21个代码模型】Map集合（Hashtable子类） 06:27&/p&&p&课时145：【第21个代码模型】Map集合（ConcurrentHashMap子类） 23:56&/p&&p&课时146：【第21个代码模型】Map集合（Map使用Iterator输出） 14:46&/p&&p&课时147：【第21个代码模型】Map集合（Map中的key实现说明） 04:18&/p&&p&课时148：【第21个代码模型】Map集合（TreeMap子类） 05:10&/p&&p&课时149：Stack栈 06:48&/p&&p&课时150：Queue队列 19:06&/p&&p&课时151：Properties属性操作 09:17&/p&&p&课时152：Collections工具类 04:29&/p&&p&课时153：Stream数据流（Collection接口扩充） 08:30&/p&&p&课时154：Stream数据流（Stream基本操作） 11:07&/p&&p&课时155：Stream数据流（MapReduce模型） 13:49&/p&&p&在阿里云大学，你可以跟随Java名师李兴华学到路线图中所有的知识点&b&（完全免费哦）&/b&，赶快开始你的Java学习之路吧！&/p&&h2&&b&更多技术课程，请关注阿里云大学专栏：&a href=&https://zhuanlan.zhihu.com/aliyunedu& class=&internal&&阿里云大学 - 知乎专栏&/a&&/b& &/h2&
阿里云大学课程： 【Java学习路线图，看你掌握了多少】附全部知识点免费视频课程这个路线图中包含了Java学习的三部曲：（点击标题学习视频课程） 总计25课课时1：Java简介（Java发展概述） 26:42课时2：Java简介（Java主要特点） 08:55课时3…
&figure&&img src=&https://pic2.zhimg.com/v2-c4d93e8db_b.jpg& data-rawwidth=&1200& data-rawheight=&630& class=&origin_image zh-lightbox-thumb& width=&1200& data-original=&https://pic2.zhimg.com/v2-c4d93e8db_r.jpg&&&/figure&&blockquote&简评：虽然说 Android 的架构选择一直都很自由，MVP、MVC、MVVM 各有拥趸。但 Google 最近还是推出了一份关于应用架构的实践指南，并给出了相当详尽的步骤和一些指导建议。希望大家都能看一看，学习一下，打造更加优秀易用的 APP，也为 Android 生态的改善做一点贡献。: )&/blockquote&&p&最近，官方推出了一份关于应用架构的最佳实践指南。这里就给大家简要介绍一下：&/p&&p&首先，Android 开发者肯定都知道 Android 中有四大组件，这些组件都有各自的生命周期并且在一定程度上是不受你控制的。在任何时候，Android 操作系统都可能根据用户的行为或资源紧张等原因回收掉这些组件。&/p&&p&这也就引出了&b&第一条准则&/b&：「不要在应用程序组件中保存任何应用数据或状态，并且组件间也不应该相互依赖」。&/p&&p&最常见的错误就是在 Activity 或 Fragment 中写了与 UI 和交互无关的代码。尽可能减少对它们的依赖，这能避免大量生命周期导致的问题，以提供更好的用户体验。&/p&&p&&b&第二条准则&/b&：「通过 model 驱动应用 UI，并尽可能的持久化」。&/p&&p&这样做主要有两个原因：&/p&&ol&&li&如果系统回收了你的应用资源或其他什么意外情况，不会导致用户丢失数据。&br&&/li&&li&Model 就应该是负责处理应用程序数据的组件。独立于视图和应用程序组件，保持了视图代码的简单，也让你的应用逻辑更容易管理。并且，将应用数据置于 model 类中，也更有利于测试。&/li&&/ol&&br&&h2&官方推荐的 App 架构&/h2&&p&在这里，官方演示了通过使用最新推出的 &a href=&http://link.zhihu.com/?target=https%3A//developer.android.com/topic/libraries/architecture/index.html& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&Architecture Components&/a& 来构建一个应用。&/p&&p&想象一下，您正在打算开发一个显示用户个人信息的界面，用户数据通过 REST API 从后端获取。&/p&&p&首先，我们需要创建三个文件：&/p&&ul&&li&user_profile.xml：定义界面。&/li&&li&UserProfileViewModel.java：数据类。&/li&&li&UserProfileFragment.java：显示 ViewModel 中的数据并对用户的交互做出反应。&br&&/li&&/ul&&br&&u&为了简单起见，我们这里就省略掉布局文件。&/u&&br&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserProfileViewModel&/span& &span class=&kd&&extends&/span& &span class=&n&&ViewModel&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&n&&User&/span& &span class=&n&&user&/span&&span class=&o&&;&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&init&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&userId&/span& &span class=&o&&=&/span& &span class=&n&&userId&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&n&&User&/span& &span class=&nf&&getUser&/span&&span class=&o&&()&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&n&&user&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserProfileFragment&/span& &span class=&kd&&extends&/span& &span class=&n&&LifecycleFragment&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&kd&&static&/span& &span class=&kd&&final&/span& &span class=&n&&String&/span& &span class=&n&&UID_KEY&/span& &span class=&o&&=&/span& &span class=&s&&&uid&&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&n&&UserProfileViewModel&/span& &span class=&n&&viewModel&/span&&span class=&o&&;&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&onActivityCreated&/span&&span class=&o&&(&/span&&span class=&nd&&@Nullable&/span& &span class=&n&&Bundle&/span& &span class=&n&&savedInstanceState&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&kd&&super&/span&&span class=&o&&.&/span&&span class=&na&&onActivityCreated&/span&&span class=&o&&(&/span&&span class=&n&&savedInstanceState&/span&&span class=&o&&);&/span&
&span class=&n&&String&/span& &span class=&n&&userId&/span& &span class=&o&&=&/span& &span class=&n&&getArguments&/span&&span class=&o&&().&/span&&span class=&na&&getString&/span&&span class=&o&&(&/span&&span class=&n&&UID_KEY&/span&&span class=&o&&);&/span&
&span class=&n&&viewModel&/span& &span class=&o&&=&/span& &span class=&n&&ViewModelProviders&/span&&span class=&o&&.&/span&&span class=&na&&of&/span&&span class=&o&&(&/span&&span class=&k&&this&/span&&span class=&o&&).&/span&&span class=&na&&get&/span&&span class=&o&&(&/span&&span class=&n&&UserProfileViewModel&/span&&span class=&o&&.&/span&&span class=&na&&class&/span&&span class=&o&&);&/span&
&span class=&n&&viewModel&/span&&span class=&o&&.&/span&&span class=&na&&init&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&public&/span& &span class=&n&&View&/span& &span class=&nf&&onCreateView&/span&&span class=&o&&(&/span&&span class=&n&&LayoutInflater&/span& &span class=&n&&inflater&/span&&span class=&o&&,&/span&
&span class=&nd&&@Nullable&/span& &span class=&n&&ViewGroup&/span& &span class=&n&&container&/span&&span class=&o&&,&/span& &span class=&nd&&@Nullable&/span& &span class=&n&&Bundle&/span& &span class=&n&&savedInstanceState&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&n&&inflater&/span&&span class=&o&&.&/span&&span class=&na&&inflate&/span&&span class=&o&&(&/span&&span class=&n&&R&/span&&span class=&o&&.&/span&&span class=&na&&layout&/span&&span class=&o&&.&/span&&span class=&na&&user_profile&/span&&span class=&o&&,&/span& &span class=&n&&container&/span&&span class=&o&&,&/span& &span class=&kc&&false&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&u&注意其中的 ViewModel 和 LifecycleFragment 都是 Android 新引入的，可以参考&a href=&http://link.zhihu.com/?target=https%3A//developer.android.com/topic/libraries/architecture/adding-components.html& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&官方说明&/a&进行集成。&/u&&p&现在，我们完成了这三个模块，该如何将它们联系起来呢？也就是当 ViewModel 中的用户字段被设置时，我们需要一种方法来通知 UI。这就是 &b&LiveData &/b&的用武之地了。&/p&&blockquote&&a href=&http://link.zhihu.com/?target=https%3A//developer.android.com/topic/libraries/architecture/livedata.html& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&LiveData&/a& 是一个可被观察的数据持有者（用到了观察者模式）。其能够允许 Activity, Fragment 等应用程序组件对其进行观察，并且不会在它们之间创建强依赖。LiveData 还能够自动响应各组件的声明周期事件，防止内存泄漏，从而使应用程序不会消耗更多的内存。&br&&br&&b&注意&/b&：LiveData 和 RxJava 或 Agera 的区别主要在于 LiveData 自动帮助处理了生命周期事件，避免了内存泄漏。&/blockquote&&p&所以，现在我们来修改一下 UserProfileViewModel：&/p&&div class=&highlight&&&pre&&code class=&language-text&&&span&&/span&public class UserProfileViewModel extends ViewModel {
private LiveData&User&
public LiveData&User& getUser() {
&/code&&/pre&&/div&&p&再在 UserProfileFragment 中对其进行观察并更新我们的 UI：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Override&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&onActivityCreated&/span&&span class=&o&&(&/span&&span class=&nd&&@Nullable&/span& &span class=&n&&Bundle&/span& &span class=&n&&savedInstanceState&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&kd&&super&/span&&span class=&o&&.&/span&&span class=&na&&onActivityCreated&/span&&span class=&o&&(&/span&&span class=&n&&savedInstanceState&/span&&span class=&o&&);&/span&
&span class=&n&&viewModel&/span&&span class=&o&&.&/span&&span class=&na&&getUser&/span&&span class=&o&&().&/span&&span class=&na&&observe&/span&&span class=&o&&(&/span&&span class=&k&&this&/span&&span class=&o&&,&/span& &span class=&n&&user&/span& &span class=&o&&-&&/span& &span class=&o&&{&/span&
&span class=&c1&&// update UI&/span&
&span class=&o&&});&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&&b&获取数据&/b&&/p&&p&现在，我们联系了 ViewModel 和 Fragment，但 ViewModel 又怎么来获取到数据呢？&/p&&p&在这个示例中，我们假定后端提供了 REST API，因此我们选用 &a href=&http://link.zhihu.com/?target=http%3A//square.github.io/retrofit/& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&Retrofit&/a& 来访问我们的后端。&/p&&p&首先，定义一个 Webservice：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&interface&/span& &span class=&nc&&Webservice&/span& &span class=&o&&{&/span&
&span class=&cm&&/**&/span&
&span class=&cm&&
* @GET declares an HTTP GET request&/span&
&span class=&cm&&
* @Path(&user&) annotation on the userId parameter marks it as a&/span&
&span class=&cm&&
* replacement for the {user} placeholder in the @GET path&/span&
&span class=&cm&&
&span class=&nd&&@GET&/span&&span class=&o&&(&/span&&span class=&s&&&/users/{user}&&/span&&span class=&o&&)&/span&
&span class=&n&&Call&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&getUser&/span&&span class=&o&&(&/span&&span class=&nd&&@Path&/span&&span class=&o&&(&/span&&span class=&s&&&user&&/span&&span class=&o&&)&/span& &span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&不要通过 ViewModel 直接来获取数据，这里我们将工作转交给一个新的 &strong&Repository&/strong& 模块。&/p&&blockquote&Repository 模块负责数据处理，为应用的其他部分提供干净可靠的 API。你可以将其考虑为不同数据源（Web，缓存或数据库）与应用之间的中间层。&/blockquote&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserRepository&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&n&&Webservice&/span& &span class=&n&&webservice&/span&&span class=&o&&;&/span&
&span class=&c1&&// ...&/span&
&span class=&kd&&public&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&getUser&/span&&span class=&o&&(&/span&&span class=&kt&&int&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&c1&&// This is not an optimal implementation, we'll fix it below&/span&
&span class=&kd&&final&/span& &span class=&n&&MutableLiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&data&/span& &span class=&o&&=&/span& &span class=&k&&new&/span& &span class=&n&&MutableLiveData&/span&&span class=&o&&&&();&/span&
&span class=&n&&webservice&/span&&span class=&o&&.&/span&&span class=&na&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&).&/span&&span class=&na&&enqueue&/span&&span class=&o&&(&/span&&span class=&k&&new&/span& &span class=&n&&Callback&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&()&/span& &span class=&o&&{&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&onResponse&/span&&span class=&o&&(&/span&&span class=&n&&Call&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&call&/span&&span class=&o&&,&/span& &span class=&n&&Response&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&response&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&c1&&// error case is left out for brevity&/span&
&span class=&n&&data&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&body&/span&&span class=&o&&());&/span&
&span class=&o&&}&/span&
&span class=&o&&});&/span&
&span class=&k&&return&/span& &span class=&n&&data&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&&b&管理组件间的依赖关系&/b&&/p&&p&根据上面的代码，我们可以看到 UserRepository 中有一个 Webservice 的实例，不要直接在 UserRepository 中 new 一个 Webservice。这很容易导致代码的重复与复杂化，比如 UserRepository 很可能不是唯一用到 Webservice 的类，如果每个用到的类都新建一个 Webservice，这显示会导致资源的浪费。&/p&&p&这里，我们推荐使用 &a href=&http://link.zhihu.com/?target=https%3A//google.github.io/dagger/& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&Dagger 2&/a& 来管理这些依赖关系。&/p&&p&现在，让我们来把 ViewModel 和 Repository 连接起来吧：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserProfileViewModel&/span& &span class=&kd&&extends&/span& &span class=&n&&ViewModel&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&user&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&n&&UserRepository&/span& &span class=&n&&userRepo&/span&&span class=&o&&;&/span&
&span class=&nd&&@Inject&/span& &span class=&c1&&// UserRepository parameter is provided by Dagger 2&/span&
&span class=&kd&&public&/span& &span class=&nf&&UserProfileViewModel&/span&&span class=&o&&(&/span&&span class=&n&&UserRepository&/span& &span class=&n&&userRepo&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&userRepo&/span& &span class=&o&&=&/span& &span class=&n&&userRepo&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&init&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&if&/span& &span class=&o&&(&/span&&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&user&/span& &span class=&o&&!=&/span& &span class=&kc&&null&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&c1&&// ViewModel is created per Fragment so&/span&
&span class=&c1&&// we know the userId won't change&/span&
&span class=&k&&return&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&n&&user&/span& &span class=&o&&=&/span& &span class=&n&&userRepo&/span&&span class=&o&&.&/span&&span class=&na&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&getUser&/span&&span class=&o&&()&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&user&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&&b&缓存数据&/b&&/p&&p&在实际项目中，Repository 往往不会只有一个数据源。因此，我们这里在其中再加入缓存：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Singleton&/span&
&span class=&c1&&// informs Dagger that this class should be constructed once&/span&
&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserRepository&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&n&&Webservice&/span& &span class=&n&&webservice&/span&&span class=&o&&;&/span&
&span class=&c1&&// simple in memory cache, details omitted for brevity&/span&
&span class=&kd&&private&/span& &span class=&n&&UserCache&/span& &span class=&n&&userCache&/span&&span class=&o&&;&/span&
&span class=&kd&&public&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&cached&/span& &span class=&o&&=&/span& &span class=&n&&userCache&/span&&span class=&o&&.&/span&&span class=&na&&get&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&k&&if&/span& &span class=&o&&(&/span&&span class=&n&&cached&/span& &span class=&o&&!=&/span& &span class=&kc&&null&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&n&&cached&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&kd&&final&/span& &span class=&n&&MutableLiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&data&/span& &span class=&o&&=&/span& &span class=&k&&new&/span& &span class=&n&&MutableLiveData&/span&&span class=&o&&&&();&/span&
&span class=&n&&userCache&/span&&span class=&o&&.&/span&&span class=&na&&put&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&,&/span& &span class=&n&&data&/span&&span class=&o&&);&/span&
&span class=&c1&&// this is still suboptimal but better than before.&/span&
&span class=&c1&&// a complete implementation must also handle the error cases.&/span&
&span class=&n&&webservice&/span&&span class=&o&&.&/span&&span class=&na&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&).&/span&&span class=&na&&enqueue&/span&&span class=&o&&(&/span&&span class=&k&&new&/span& &span class=&n&&Callback&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&()&/span& &span class=&o&&{&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&public&/span& &span class=&kt&&void&/span& &span class=&nf&&onResponse&/span&&span class=&o&&(&/span&&span class=&n&&Call&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&call&/span&&span class=&o&&,&/span& &span class=&n&&Response&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&n&&response&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&data&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&body&/span&&span class=&o&&());&/span&
&span class=&o&&}&/span&
&span class=&o&&});&/span&
&span class=&k&&return&/span& &span class=&n&&data&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&&b&持久化数据&/b&&/p&&p&现在当用户旋转屏幕或暂时离开应用再回来时，数据是直接可见的，因为是直接从缓存中获取的数据。但要是用户长时间关闭应用，并且 Android 还彻底杀死了进程呢？&/p&&p&我们目前的实现中，会再次从网络中获取数据。这可不是一个好的用户体验。这时就需要数据持久化了。继续引入一个新组件 &strong&&a href=&http://link.zhihu.com/?target=https%3A//developer.android.com/topic/libraries/architecture/room.html& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&Room&/a&。&/strong&&/p&&blockquote&Room 能帮助我们方便的实现本地数据持久化，抽象出了很多常用的数据库操作，并且在编译时会验证每个查询，从而损坏的 SQL 查询只会导致编译时错误，而不是运行时崩溃。还能和上面介绍的 LiveData 完美合作，并帮开发者处理了很多线程问题。&/blockquote&&p&现在，让我们来看看怎么使用 Room 吧。: )&/p&&p&首先，在 User 类上面加上 @Entity，将 User 声明为你数据库中的一张表。&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Entity&/span&
&span class=&kd&&class&/span& &span class=&nc&&User&/span& &span class=&o&&{&/span&
&span class=&nd&&@PrimaryKey&/span&
&span class=&kd&&private&/span& &span class=&kt&&int&/span& &span class=&n&&id&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&n&&String&/span& &span class=&n&&name&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&n&&String&/span& &span class=&n&&lastName&/span&&span class=&o&&;&/span&
&span class=&c1&&// getters and setters for fields&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&再创建数据库类并继承 &a href=&http://link.zhihu.com/?target=https%3A//developer.android.com/reference/android/arch/persistence/room/RoomDatabase.html& class=& wrap external& target=&_blank& rel=&nofollow noreferrer&&RoomDatabase&/a&：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Database&/span&&span class=&o&&(&/span&&span class=&n&&entities&/span& &span class=&o&&=&/span& &span class=&o&&{&/span&&span class=&n&&User&/span&&span class=&o&&.&/span&&span class=&na&&class&/span&&span class=&o&&},&/span& &span class=&n&&version&/span& &span class=&o&&=&/span& &span class=&mi&&1&/span&&span class=&o&&)&/span&
&span class=&kd&&public&/span& &span class=&kd&&abstract&/span& &span class=&kd&&class&/span& &span class=&nc&&MyDatabase&/span& &span class=&kd&&extends&/span& &span class=&n&&RoomDatabase&/span& &span class=&o&&{&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&注意 MyDatabase 是一个抽象类，Room 会自动添加实现的。&/p&&p&现在我们需要一种方法来将用户数据插入到数据库：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Dao&/span&
&span class=&kd&&public&/span& &span class=&kd&&interface&/span& &span class=&nc&&UserDao&/span& &span class=&o&&{&/span&
&span class=&nd&&@Insert&/span&&span class=&o&&(&/span&&span class=&n&&onConflict&/span& &span class=&o&&=&/span& &span class=&n&&REPLACE&/span&&span class=&o&&)&/span&
&span class=&kt&&void&/span& &span class=&nf&&save&/span&&span class=&o&&(&/span&&span class=&n&&User&/span& &span class=&n&&user&/span&&span class=&o&&);&/span&
&span class=&nd&&@Query&/span&&span class=&o&&(&/span&&span class=&s&&&SELECT * FROM user WHERE id = :userId&&/span&&span class=&o&&)&/span&
&span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&load&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&再在数据库类中加入 DAO：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Database&/span&&span class=&o&&(&/span&&span class=&n&&entities&/span& &span class=&o&&=&/span& &span class=&o&&{&/span&&span class=&n&&User&/span&&span class=&o&&.&/span&&span class=&na&&class&/span&&span class=&o&&},&/span& &span class=&n&&version&/span& &span class=&o&&=&/span& &span class=&mi&&1&/span&&span class=&o&&)&/span&
&span class=&kd&&public&/span& &span class=&kd&&abstract&/span& &span class=&kd&&class&/span& &span class=&nc&&MyDatabase&/span& &span class=&kd&&extends&/span& &span class=&n&&RoomDatabase&/span& &span class=&o&&{&/span&
&span class=&kd&&public&/span& &span class=&kd&&abstract&/span& &span class=&n&&UserDao&/span& &span class=&nf&&userDao&/span&&span class=&o&&();&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&注意上面的 load 方法返回的是 LiveData&User&，Room 会知道什么时候数据库发生了变化并自动通知所有的观察者。这也就是 LiveData 和 Room 搭配的妙用。&/p&&p&现在继续修改 UserRepository：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&nd&&@Singleton&/span&
&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&UserRepository&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&kd&&final&/span& &span class=&n&&Webservice&/span& &span class=&n&&webservice&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&kd&&final&/span& &span class=&n&&UserDao&/span& &span class=&n&&userDao&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&kd&&final&/span& &span class=&n&&Executor&/span& &span class=&n&&executor&/span&&span class=&o&&;&/span&
&span class=&nd&&@Inject&/span&
&span class=&kd&&public&/span& &span class=&nf&&UserRepository&/span&&span class=&o&&(&/span&&span class=&n&&Webservice&/span& &span class=&n&&webservice&/span&&span class=&o&&,&/span& &span class=&n&&UserDao&/span& &span class=&n&&userDao&/span&&span class=&o&&,&/span& &span class=&n&&Executor&/span& &span class=&n&&executor&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&webservice&/span& &span class=&o&&=&/span& &span class=&n&&webservice&/span&&span class=&o&&;&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&userDao&/span& &span class=&o&&=&/span& &span class=&n&&userDao&/span&&span class=&o&&;&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&executor&/span& &span class=&o&&=&/span& &span class=&n&&executor&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&User&/span&&span class=&o&&&&/span& &span class=&nf&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&refreshUser&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&c1&&// return a LiveData directly from the database.&/span&
&span class=&k&&return&/span& &span class=&n&&userDao&/span&&span class=&o&&.&/span&&span class=&na&&load&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&kd&&private&/span& &span class=&kt&&void&/span& &span class=&nf&&refreshUser&/span&&span class=&o&&(&/span&&span class=&kd&&final&/span& &span class=&n&&String&/span& &span class=&n&&userId&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&executor&/span&&span class=&o&&.&/span&&span class=&na&&execute&/span&&span class=&o&&(()&/span& &span class=&o&&-&&/span& &span class=&o&&{&/span&
&span class=&c1&&// running in a background thread&/span&
&span class=&c1&&// check if user was fetched recently&/span&
&span class=&kt&&boolean&/span& &span class=&n&&userExists&/span& &span class=&o&&=&/span& &span class=&n&&userDao&/span&&span class=&o&&.&/span&&span class=&na&&hasUser&/span&&span class=&o&&(&/span&&span class=&n&&FRESH_TIMEOUT&/span&&span class=&o&&);&/span&
&span class=&k&&if&/span& &span class=&o&&(!&/span&&span class=&n&&userExists&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&c1&&// refresh the data&/span&
&span class=&n&&Response&/span& &span class=&n&&response&/span& &span class=&o&&=&/span& &span class=&n&&webservice&/span&&span class=&o&&.&/span&&span class=&na&&getUser&/span&&span class=&o&&(&/span&&span class=&n&&userId&/span&&span class=&o&&).&/span&&span class=&na&&execute&/span&&span class=&o&&();&/span&
&span class=&c1&&// TODO check for error etc.&/span&
&span class=&c1&&// Update the database.The LiveData will automatically refresh so&/span&
&span class=&c1&&// we don't need to do anything else here besides updating the database&/span&
&span class=&n&&userDao&/span&&span class=&o&&.&/span&&span class=&na&&save&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&body&/span&&span class=&o&&());&/span&
&span class=&o&&}&/span&
&span class=&o&&});&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&可以看到，即使我们更改了 UserRepository 中的数据源，我们也完全不需要修改 ViewModel 和 Fragment，这就是抽象的好处。同时还非常适合测试，我们可以在测试 UserProfileViewModel 时提供测试用的 UserRepository。&/p&&blockquote&下面部分的内容在原文中是作为附录，但我个人觉得也很重要，所以擅自挪上来，一起为大家介绍了。: )&/blockquote&&p&在上面的例子中，有心的大家可能发现了我们没有处理网络错误和正在加载状态。但在实际开发中其实是很重要的。这里，我们就实现一个工具类来根据不同的网络状况选择不同的数据源。&/p&&p&首先，实现一个 Resource 类：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&c1&&//a generic class that describes a data with a status&/span&
&span class=&kd&&public&/span& &span class=&kd&&class&/span& &span class=&nc&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&o&&{&/span&
&span class=&nd&&@NonNull&/span& &span class=&kd&&public&/span& &span class=&kd&&final&/span& &span class=&n&&Status&/span& &span class=&n&&status&/span&&span class=&o&&;&/span&
&span class=&nd&&@Nullable&/span& &span class=&kd&&public&/span& &span class=&kd&&final&/span& &span class=&n&&T&/span& &span class=&n&&data&/span&&span class=&o&&;&/span&
&span class=&nd&&@Nullable&/span& &span class=&kd&&public&/span& &span class=&kd&&final&/span& &span class=&n&&String&/span& &span class=&n&&message&/span&&span class=&o&&;&/span&
&span class=&kd&&private&/span& &span class=&nf&&Resource&/span&&span class=&o&&(&/span&&span class=&nd&&@NonNull&/span& &span class=&n&&Status&/span& &span class=&n&&status&/span&&span class=&o&&,&/span& &span class=&nd&&@Nullable&/span& &span class=&n&&T&/span& &span class=&n&&data&/span&&span class=&o&&,&/span& &span class=&nd&&@Nullable&/span& &span class=&n&&String&/span& &span class=&n&&message&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&status&/span& &span class=&o&&=&/span& &span class=&n&&status&/span&&span class=&o&&;&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&data&/span& &span class=&o&&=&/span& &span class=&n&&data&/span&&span class=&o&&;&/span&
&span class=&k&&this&/span&&span class=&o&&.&/span&&span class=&na&&message&/span& &span class=&o&&=&/span& &span class=&n&&message&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&kd&&static&/span& &span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&n&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&nf&&success&/span&&span class=&o&&(&/span&&span class=&nd&&@NonNull&/span& &span class=&n&&T&/span& &span class=&n&&data&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&k&&new&/span& &span class=&n&&Resource&/span&&span class=&o&&&&(&/span&&span class=&n&&SUCCESS&/span&&span class=&o&&,&/span& &span class=&n&&data&/span&&span class=&o&&,&/span& &span class=&kc&&null&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&kd&&static&/span& &span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&n&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&nf&&error&/span&&span class=&o&&(&/span&&span class=&n&&String&/span& &span class=&n&&msg&/span&&span class=&o&&,&/span& &span class=&nd&&@Nullable&/span& &span class=&n&&T&/span& &span class=&n&&data&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&k&&new&/span& &span class=&n&&Resource&/span&&span class=&o&&&&(&/span&&span class=&n&&ERROR&/span&&span class=&o&&,&/span& &span class=&n&&data&/span&&span class=&o&&,&/span& &span class=&n&&msg&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&kd&&public&/span& &span class=&kd&&static&/span& &span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&n&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&T&/span&&span class=&o&&&&/span& &span class=&nf&&loading&/span&&span class=&o&&(&/span&&span class=&nd&&@Nullable&/span& &span class=&n&&T&/span& &span class=&n&&data&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&k&&new&/span& &span class=&n&&Resource&/span&&span class=&o&&&&(&/span&&span class=&n&&LOADING&/span&&span class=&o&&,&/span& &span class=&n&&data&/span&&span class=&o&&,&/span& &span class=&kc&&null&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&因为，从网络加载数据和从磁盘加载是很相似的，所以再新建一个 NetworkBoundResource 类，方便多处复用。下面是 NetworkBoundResource 的决策树：&/p&&p&&figure&&img data-rawwidth=&534& data-rawheight=&465& src=&http://pic4.zhimg.com/v2-fc7fbc0139441cab1ea3_b.png& class=&origin_image zh-lightbox-thumb& width=&534& data-original=&http://pic4.zhimg.com/v2-fc7fbc0139441cab1ea3_r.png&&&/figure&API 设计：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&c1&&// ResultType: Type for the Resource data&/span&
&span class=&c1&&// RequestType: Type for the API response&/span&
&span class=&kd&&public&/span& &span class=&kd&&abstract&/span& &span class=&kd&&class&/span& &span class=&nc&&NetworkBoundResource&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&,&/span& &span class=&n&&RequestType&/span&&span class=&o&&&&/span& &span class=&o&&{&/span&
&span class=&c1&&// Called to save the result of the API response into the database&/span&
&span class=&nd&&@WorkerThread&/span&
&span class=&kd&&protected&/span& &span class=&kd&&abstract&/span& &span class=&kt&&void&/span& &span class=&nf&&saveCallResult&/span&&span class=&o&&(&/span&&span class=&nd&&@NonNull&/span& &span class=&n&&RequestType&/span& &span class=&n&&item&/span&&span class=&o&&);&/span&
&span class=&c1&&// Called with the data in the database to decide whether it should be&/span&
&span class=&c1&&// fetched from the network.&/span&
&span class=&nd&&@MainThread&/span&
&span class=&kd&&protected&/span& &span class=&kd&&abstract&/span& &span class=&kt&&boolean&/span& &span class=&nf&&shouldFetch&/span&&span class=&o&&(&/span&&span class=&nd&&@Nullable&/span& &span class=&n&&ResultType&/span& &span class=&n&&data&/span&&span class=&o&&);&/span&
&span class=&c1&&// Called to get the cached data from the database&/span&
&span class=&nd&&@NonNull&/span& &span class=&nd&&@MainThread&/span&
&span class=&kd&&protected&/span& &span class=&kd&&abstract&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&&&/span& &span class=&nf&&loadFromDb&/span&&span class=&o&&();&/span&
&span class=&c1&&// Called to create the API call.&/span&
&span class=&nd&&@NonNull&/span& &span class=&nd&&@MainThread&/span&
&span class=&kd&&protected&/span& &span class=&kd&&abstract&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&ApiResponse&/span&&span class=&o&&&&/span&&span class=&n&&RequestType&/span&&span class=&o&&&&&/span& &span class=&nf&&createCall&/span&&span class=&o&&();&/span&
&span class=&c1&&// Called when the fetch fails. The child class may want to reset components&/span&
&span class=&c1&&// like rate limiter.&/span&
&span class=&nd&&@MainThread&/span&
&span class=&kd&&protected&/span& &span class=&kt&&void&/span& &span class=&nf&&onFetchFailed&/span&&span class=&o&&()&/span& &span class=&o&&{&/span&
&span class=&o&&}&/span&
&span class=&c1&&// returns a LiveData that represents the resource&/span&
&span class=&kd&&public&/span& &span class=&kd&&final&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&&&&/span& &span class=&nf&&getAsLiveData&/span&&span class=&o&&()&/span& &span class=&o&&{&/span&
&span class=&k&&return&/span& &span class=&n&&result&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&o&&}&/span&
&/code&&/pre&&/div&&p&注意上面使用了 ApiResponse 作为网络请求， ApiResponse 是对于 Retrofit2.Call 的简单包装，用于将其响应转换为 LiveData。&/p&&p&下面是具体的实现：&/p&&div class=&highlight&&&pre&&code class=&language-java&&&span&&/span&&span class=&kd&&public&/span& &span class=&kd&&abstract&/span& &span class=&kd&&class&/span& &span class=&nc&&NetworkBoundResource&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&,&/span& &span class=&n&&RequestType&/span&&span class=&o&&&&/span& &span class=&o&&{&/span&
&span class=&kd&&private&/span& &span class=&kd&&final&/span& &span class=&n&&MediatorLiveData&/span&&span class=&o&&&&/span&&span class=&n&&Resource&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&&&&/span& &span class=&n&&result&/span& &span class=&o&&=&/span& &span class=&k&&new&/span& &span class=&n&&MediatorLiveData&/span&&span class=&o&&&&();&/span&
&span class=&nd&&@MainThread&/span&
&span class=&n&&NetworkBoundResource&/span&&span class=&o&&()&/span& &span class=&o&&{&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&&span class=&n&&Resource&/span&&span class=&o&&.&/span&&span class=&na&&loading&/span&&span class=&o&&(&/span&&span class=&kc&&null&/span&&span class=&o&&));&/span&
&span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&&&/span& &span class=&n&&dbSource&/span& &span class=&o&&=&/span& &span class=&n&&loadFromDb&/span&&span class=&o&&();&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&addSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&,&/span& &span class=&n&&data&/span& &span class=&o&&-&&/span& &span class=&o&&{&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&removeSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&);&/span&
&span class=&k&&if&/span& &span class=&o&&(&/span&&span class=&n&&shouldFetch&/span&&span class=&o&&(&/span&&span class=&n&&data&/span&&span class=&o&&))&/span& &span class=&o&&{&/span&
&span class=&n&&fetchFromNetwork&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span& &span class=&k&&else&/span& &span class=&o&&{&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&addSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&,&/span&
&span class=&n&&newData&/span& &span class=&o&&-&&/span& &span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&&span class=&n&&Resource&/span&&span class=&o&&.&/span&&span class=&na&&success&/span&&span class=&o&&(&/span&&span class=&n&&newData&/span&&span class=&o&&)));&/span&
&span class=&o&&}&/span&
&span class=&o&&});&/span&
&span class=&o&&}&/span&
&span class=&kd&&private&/span& &span class=&kt&&void&/span& &span class=&nf&&fetchFromNetwork&/span&&span class=&o&&(&/span&&span class=&kd&&final&/span& &span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&ResultType&/span&&span class=&o&&&&/span& &span class=&n&&dbSource&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&LiveData&/span&&span class=&o&&&&/span&&span class=&n&&ApiResponse&/span&&span class=&o&&&&/span&&span class=&n&&RequestType&/span&&span class=&o&&&&&/span& &span class=&n&&apiResponse&/span& &span class=&o&&=&/span& &span class=&n&&createCall&/span&&span class=&o&&();&/span&
&span class=&c1&&// we re-attach dbSource as a new source,&/span&
&span class=&c1&&// it will dispatch its latest value quickly&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&addSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&,&/span&
&span class=&n&&newData&/span& &span class=&o&&-&&/span& &span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&&span class=&n&&Resource&/span&&span class=&o&&.&/span&&span class=&na&&loading&/span&&span class=&o&&(&/span&&span class=&n&&newData&/span&&span class=&o&&)));&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&addSource&/span&&span class=&o&&(&/span&&span class=&n&&apiResponse&/span&&span class=&o&&,&/span& &span class=&n&&response&/span& &span class=&o&&-&&/span& &span class=&o&&{&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&removeSource&/span&&span class=&o&&(&/span&&span class=&n&&apiResponse&/span&&span class=&o&&);&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&removeSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&);&/span&
&span class=&c1&&//noinspection ConstantConditions&/span&
&span class=&k&&if&/span& &span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&isSuccessful&/span&&span class=&o&&())&/span& &span class=&o&&{&/span&
&span class=&n&&saveResultAndReInit&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&);&/span&
&span class=&o&&}&/span& &span class=&k&&else&/span& &span class=&o&&{&/span&
&span class=&n&&onFetchFailed&/span&&span class=&o&&();&/span&
&span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&addSource&/span&&span class=&o&&(&/span&&span class=&n&&dbSource&/span&&span class=&o&&,&/span&
&span class=&n&&newData&/span& &span class=&o&&-&&/span& &span class=&n&&result&/span&&span class=&o&&.&/span&&span class=&na&&setValue&/span&&span class=&o&&(&/span&
&span class=&n&&Resource&/span&&span class=&o&&.&/span&&span class=&na&&error&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&errorMessage&/span&&span class=&o&&,&/span& &span class=&n&&newData&/span&&span class=&o&&)));&/span&
&span class=&o&&}&/span&
&span class=&o&&});&/span&
&span class=&o&&}&/span&
&span class=&nd&&@MainThread&/span&
&span class=&kd&&private&/span& &span class=&kt&&void&/span& &span class=&nf&&saveResultAndReInit&/span&&span class=&o&&(&/span&&span class=&n&&ApiResponse&/span&&span class=&o&&&&/span&&span class=&n&&RequestType&/span&&span class=&o&&&&/span& &span class=&n&&response&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&k&&new&/span& &span class=&n&&AsyncTask&/span&&span class=&o&&&&/span&&span class=&n&&Void&/span&&span class=&o&&,&/span& &span class=&n&&Void&/span&&span class=&o&&,&/span& &span class=&n&&Void&/span&&span class=&o&&&()&/span& &span class=&o&&{&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&protected&/span& &span class=&n&&Void&/span& &span class=&nf&&doInBackground&/span&&span class=&o&&(&/span&&span class=&n&&Void&/span&&span class=&o&&...&/span& &span class=&n&&voids&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&n&&saveCallResult&/span&&span class=&o&&(&/span&&span class=&n&&response&/span&&span class=&o&&.&/span&&span class=&na&&body&/span&&span class=&o&&);&/span&
&span class=&k&&return&/span& &span class=&kc&&null&/span&&span class=&o&&;&/span&
&span class=&o&&}&/span&
&span class=&nd&&@Override&/span&
&span class=&kd&&protected&/span& &span class=&kt&&void&/span& &span class=&nf&&onPostExecute&/span&&span class=&o&&(&/span&&span class=&n&&Void&/span& &span class=&n&&aVoid&/span&&span class=&o&&)&/span& &span class=&o&&{&/span&
&span class=&c1&&// we specially request a new live data,&/span&
&span class=&c1&&// otherwise we will get immediately last cached value,&/span&
&span class=&c1&&// which may not be updated with latest results received from n