Android Architecture Components 只看这一篇就够了

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原作者:Boy·哈利波特

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一、前言


1.1、Android Architecture Components 介绍

Android Architecture Components 是谷歌在Google I/O 2017发布一套帮助开发者解决Android 架构设计的方案。里面包含了两大块内容:

  • 生命周期相关的 Lifecycle-aware Components
  • 数据库解决方案 Room

1.2、组件功能

官方给予 Google 组件的功能:A collection of libraries that help you design robust, testable, and maintainable apps. Start with classes for managing your UI component lifecycle and handling data persistence。

使用Google 提供的处理数据持久化和管理组件生命周期的类,有助于应用开发者们构建更加鲁棒性,可测的,稳定可靠的应用。

提供主要的组件有:

  • Lifecycle:管理组件生命周期
  • Room: 持久化数据结构

1.3、主要架构

1.4、使用组件

在项目根目录 build.gradle 文件添加仓库依赖:

allprojects {
    repositories {
        jcenter()
        google()
    }
}

如果遇到如下因 gradle 版本导致的编译失败问题:

Error:(6, 1) A problem occurred evaluating root project 'TestArc'.>
Could not find method google() for arguments [] on repository container;

可修改为:

maven {
   url 'https://maven.google.com'
}

然后在主 module 的 build.gradle 文件添加需要依赖的组件:

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:26.+'

    def lifecycle_version = "1.1.1"

    // ViewModel and LiveData
    compile "android.arch.lifecycle:extensions:$lifecycle_version"
    // alternatively - just ViewModel
    compile "android.arch.lifecycle:viewmodel:$lifecycle_version" // use -ktx for Kotlin
    // alternatively - just LiveData
    compile "android.arch.lifecycle:livedata:$lifecycle_version"
    // alternatively - Lifecycles only (no ViewModel or LiveData).
    // Support library depends on this lightweight import
    compile "android.arch.lifecycle:runtime:$lifecycle_version"

    annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"
    // alternately - if using Java8, use the following instead of compiler
    compile "android.arch.lifecycle:common-java8:$lifecycle_version"

    // optional - ReactiveStreams support for LiveData
    compile "android.arch.lifecycle:reactivestreams:$lifecycle_version"

    // optional - Test helpers for LiveData
    // compile "android.arch.core:core-testing:$lifecycle_version"
    compile 'com.squareup.retrofit2:retrofit:2.1.0'

    compile 'com.squareup.retrofit2:converter-gson:2.1.0'
    compile 'com.facebook.stetho:stetho:1.3.1'

    //  room
    compile 'android.arch.persistence.room:runtime:1.1.0'
    annotationProcessor 'android.arch.persistence.room:compiler:1.1.0'
    compile "android.arch.persistence.room:rxjava2:1.1.0"
}

二、Lifecycle 管理生命周期


2.1、Lifecycle 介绍

Lifecycle 组件指的是 android.arch.lifecycle 包下提供的各种类与接口,可以让开发者构建能感知其他组件(主要指Activity 、Fragment)生命周期(lifecycle-aware)的类。

2.2、常规 MVP Presenter 使用

比如我们需要监听某个 Activity 生命周期的变化,在生命周期改变的时候打印日志,一般做法构造回调的方式,先定义基础 BaseActivityPresenter 接口:

public interface BaseActivityPresenter extends BasePresenter{

    void onCreate();

    void onStart();

    void onResume();

    void onPause();

    void onStop();

    void onDestroy();

}

在实现类中增加自定义操作(打印日志):

public class ActivityPresenter implements BaseActivityPresenter {

    private static String TAG = ActivityPresenter.class.getSimpleName();

    @Override
    public void onCreate() {
        LogUtil.i(TAG, "onCreate()");
    }

    @Override
    public void onStart() {
        LogUtil.i(TAG, "onStart()");
    }

    @Override
    public void onResume() {
        LogUtil.i(TAG, "onResume()");
    }

    @Override
    public void onPause() {
        LogUtil.i(TAG, "onPause()");
    }

    @Override
    public void onStop() {
        LogUtil.i(TAG, "onStop()");
    }

    @Override
    public void onDestroy() {
        LogUtil.i(TAG, "onDestroy()");
    }

}

然后在需要监听的 Activity 中依次回调方法:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mBasePresenter = new ActivityPresenter();
    }

    @Override
    protected void onStart() {
        super.onStart();
        mBasePresenter.onStart();
    }

    @Override
    protected void onResume() {
        super.onResume();
        mBasePresenter.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mBasePresenter.onPause();
    }

    @Override
    protected void onStop() {
        super.onStop();
        mBasePresenter.onStop();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mBasePresenter.onDestroy();
    }

在 Activity 的 onCreate() 方法中创建 BasePresenter,监听 Activity 的生命周期方法。

2.3、使用 Lifecycle

上述写可以实现基础的功能,但是不够灵活,假如除了 ActivityPresenter 类,还有别的类要监听 Activity 生命周期变化,那也需要添加许多生命周期的回调方法,比较繁琐。那我们是否可以当 Activity 生命周期发生变化的时候主动通知需求方呢?答案就是使用 Lifecycle 提供的 LifecycleObserver:

public class ActivityLifeObserver implements BaseActivityPresenter,
 LifecycleObserver {

    private String TAG = ActivityLifeObserver.class.getSimpleName();

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    @Override
    public void onCreate() {
        LogUtil.i(TAG, "onCreate()");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    @Override
    public void onStart() {
        LogUtil.i(TAG, "onStart()");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    @Override
    public void onResume() {
        LogUtil.i(TAG, "onResume()");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    @Override
    public void onPause() {
        LogUtil.i(TAG, "onPause()");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    @Override
    public void onStop() {
        LogUtil.i(TAG, "onStop()");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    @Override
    public void onDestroy() {
        LogUtil.i(TAG, "onDestroy()");
    }

}

让我们的业务类实现 ActivityLifeObserver 接口,同时在每一个方法实现上增加 @OnLifecycleEvent(Lifecycle.Event.XXXX)注解,OnLifecycleEvent 对应了 Activity 的生命周期方法。被监听的 Actiivty 实现 LifecycleOwner 接口,然后在需要监听的 Activity 中注册:

public class DetailActivity extends AppCompatActivity implements LifecycleOwner{

    private static String TAG = DetailActivity.class.getSimpleName();
    private LifecycleRegistry mLifecycleRegistry;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);
        mLifecycleRegistry = new LifecycleRegistry(this);
        // 注册需要监听的 Observer 
        mLifecycleRegistry.addObserver(new ActivityLifeObserver());
        mLifecycleRegistry.addObserver(new LocationLifeObserver());
    }

    @Override
    public Lifecycle getLifecycle() {
        return mLifecycleRegistry;
    }
}

运行如下:

com.troy.androidrc I/ActivityLifeObserver: onCreate()
com.troy.androidrc I/ActivityLifeObserver: onStart()
com.troy.androidrc I/ActivityLifeObserver: onResume()
com.troy.androidrc I/ActivityLifeObserver: onPause()
com.troy.androidrc I/ActivityLifeObserver: onStop()
com.troy.androidrc I/ActivityLifeObserver: onDestroy()

其中 Lifecycle 使用两个主要的枚举类来表示其所关联组件的生命周期:

  • Event 事件 从组件或者Lifecycle类分发出来的生命周期,它们和Activity/Fragment生命周期的事件一一对应。(ON_CREATE, ON_START, ON_RESUME, ON_PAUSE, ON_STOP, ON_DESTROY);
  • State 状态 当前组件的生命周期状态(INITIALIZED, DESTROYED, CREATED, STARTED, RESUMED)。

LifecycleRegistry 类用于注册和反注册需要观察当前组件生命周期的 Observer,用法如下:

//  初始化
mLifecycleRegistry = new LifecycleRegistry(this);
mActivityLifeObserver = new ActivityLifeObserver();
//  注册观察者
mLifecycleRegistry.addObserver(mActivityLifeObserver);
mLifecycleRegistry.addObserver(new LocationLifeObserver());
//  移除观察者
mLifecycleRegistry.removeObserver(mActivityLifeObserver);

三、LiveData && ViewModel


3.1、LiveData && ViewModel 介绍

LiveData 是一种持有可被观察数据的类(an observable data holder class)。和其他可被观察的类不同的是,LiveData是有生命周期感知能力的(lifecycle-aware,),这意味着它可以在 activities, fragments, 或者 services 生命周期是活跃状态时更新这些组件。

ViewModel 与 LiveData 之间的关系图如下:

3.2、LiveData && ViewModel 使用

在 Activity 页面有一 TextView,需要展示用户 User 的信息,User 类定义:

public class User {

    public String userId;

    public String name;

    public String phone;

    @Override
    public String toString() {
        return "User{" +
                "userId='" + userId + '\'' +
                ", name='" + name + '\'' +
                ", phone='" + phone + '\'' +
                '}';
    }
}

常规的做法:

// 获取 User 的数据后
mTvUser.setText(user.toString());

这样做的一个问题,如果获取或者修改 User 的来源不止一处,那么需要在多个地方更新 TextView,并且如果在多处 UI 用到了 User,那么也需要在多处更新。

使用 LiveData 与 ViewModel 的组合,将LiveData 持有 User 实体,作为一个被观察者,当 User 改变时,所有使用 User 的地方自动 change。构建一个 UserViewModel 如下:

public class UserViewModel extends ViewModel
 implements BaseViewModel<User> {

    private String TAG = UserViewModel.class.getSimpleName();

    private MutableLiveData<User> liveUser;

    public MutableLiveData<User> getData(){
        if(liveUser == null){
            liveUser = new MutableLiveData<User>();
        }

        liveUser.setValue(loadData());
        return this.liveUser;
    }

    public void changeData(){
        if(liveUser != null){
            liveUser.setValue(loadData());
        }
    }

    @Override
    public User loadData() {
        User user = new User();
        user.userId = RandomUtil.getRandomNumber();
        user.name = RandomUtil.getChineseName();
        user.phone = RandomUtil.getRandomPhone();
        LogUtil.i(TAG, "loadData(): " + user.toString());
        return user;
    }

    @Override
    public void clearData() {

    }
}

自定义的UserViewModel 继承系统的 ViewModel,将 User 封装成 MutableLiveData: if(liveUser == null){ liveUser = new MutableLiveData<User>(); }

在使用User 的地方增加观察:

//  view model.observe
mUserViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
mUserViewModel.getData().observe(this, new Observer<User>() {
   @Override
   public void onChanged(@Nullable User user) {
       if(user != null){
           mTvUser.setText(user.toString());
       }
   }
});

数据源发送改变的时候:

//	改变 User 内容
mButtonUser.setOnClickListener(new View.OnClickListener() {
     @Override
     public void onClick(View v) {
         if(mUserViewModel != null && mUserViewModel.getData() != null){
             mUserViewModel.changeData();
         }
     }
});

//	setValue
public void changeData(){
   if(liveUser != null){
        liveUser.setValue(loadData());
    }
}

这样使用到 User 的地方,UI 会自动更新,日志如下:

com.troy.androidrc I/DetailActivity:
 User{userId='9372622', name='邓楠', phone='15607043749'}

com.troy.androidrc I/DetailActivity:
 User{userId='6099877', name='文瑾慧', phone='13005794027'}

四、Room


4.1、Room 介绍

Room 持久层库提供了一个方便我们访问 SQLite 数据库的抽象层(an abstraction layer ),帮助我们更好的在 APP 上创建我们的数据缓存,能够让 APP 即使在没有网络的情况也能正常使用。

Room 的架构如下:

4.2、Room 使用与主要注解

创建包含订单表的数据库如下步骤:

1、创建 Order.java:

@Entity(tableName = "orders")
public class Order {

    @PrimaryKey
    @ColumnInfo(name = "order_id")
    public long orderId;

    @ColumnInfo(name = "address")
    public String address;

    @ColumnInfo(name = "owner_name")
    public String ownerName;

    @ColumnInfo(name = "owner_phone")
    public String ownerPhone;

    //  指示 Room 需要忽略的字段或方法
    @Ignore
    public String ignoreText;

    @Embedded
    public OwnerAddress ownerAddress;
}

2、创建 OrderDao:

@Dao
public interface OrderDao {

    @Query("SELECT * FROM orders")
    List<Order> loadAllOrders();

    @Insert
    void insertAll(Order... orders);

    @Query("SELECT * FROM orders WHERE order_id IN (:orderIds)")
    List<Order> queryOrderById(long[] orderIds);

    @Delete
    void deleteOrder(Order... orders);

    @Update
    void updateOrder(Order... orders);
}

3、创建数据库

@Database(entities = {Order.class, AddressInfo.class}, version = 2)
public abstract class AppDatabase extends RoomDatabase{

   public abstract OrderDao getOrderDao();
   
}

// 实现类
public static void buildDb(){
DB_INSTANCE = Room.
    databaseBuilder(TroyApplication.getInstance(), AppDatabase.class, "troy_db")   //  指定数据库名称
    .addCallback(new RoomDatabase.Callback() {
        @Override
        public void onCreate(@NonNull SupportSQLiteDatabase db) {
            super.onCreate(db);  //  数据库创建回调;
            LogUtil.i(TAG, "onCreate");
        }

        @Override
        public void onOpen(@NonNull SupportSQLiteDatabase db) {
            super.onOpen(db);   //  数据库使用回调;
            LogUtil.i(TAG, "onOpen");
        }
    })
    .allowMainThreadQueries()   // 数据库操作可运行在主线程
    .build();

}

使用到的主要注解:

  • @Entity(tableName = "orders") // 定义表名;
  • @PrimaryKey // 定义主键;
  • @ColumnInfo(name = "order_id") // 定义数据表中的字段名;
  • @Ignore // 指示 Room 需要忽略的字段或方法;
  • @Embedded // 指定嵌入实体
  • @Query("SELECT * FROM orders") // 定义查询数据接口;
  • @Insert // 定义增加数据接口;
  • @Delete // 定义删除数据接口;
  • @Update // 定义更新数据接口;
  • @Database // 定义数据库信息,表信息,数据库版本

3.3、增删改查实现

增:

//  1、插入接口声明
@Insert
void insertAll(Order... orders);

//  2、插入接口实现
@Override
  public void insertAll(Order... orders) {
    __db.beginTransaction();
    try {
      __insertionAdapterOfOrder.insert(orders);
      __db.setTransactionSuccessful();
    } finally {
      __db.endTransaction();
    }
}

//  3、插入接口调用
AppDatabase db = DbManager.getDbInstance();
OrderDao orderDao = db.getOrderDao();
Order order = Order.createNewOrder();
orderDao.insertAll(order);

删:

//	1、删除接口声明
@Delete
void deleteOrder(Order... orders);

//	2、删除接口实现
@Override
  public void deleteOrder(Order... orders) {
    __db.beginTransaction();
    try {
      __deletionAdapterOfOrder.handleMultiple(orders);
      __db.setTransactionSuccessful();
    } finally {
      __db.endTransaction();
    }
}

//	3、删除接口调用
AppDatabase db = DbManager.getDbInstance();
OrderDao orderDao = db.getOrderDao();
orderDao.deleteOrder(orderList.get(orderList.size() - 1));

改:

//	1、修改接口声明
 @Update
 void updateOrder(Order... orders);

//	2、修改接口实现
@Override
  public void updateOrder(Order... orders) {
    __db.beginTransaction();
    try {
      __updateAdapterOfOrder.handleMultiple(orders);
      __db.setTransactionSuccessful();
    } finally {
      __db.endTransaction();
    }
}

//	3、修改接口调用
AppDatabase db = DbManager.getDbInstance();
OrderDao orderDao = db.getOrderDao();
Order order = orderList.get(orderList.size() - 1);
order.ownerName = "update - " + RandomUtil.getChineseName();
orderDao.updateOrder(order);

查:

//	1、查询接口声明
@Query("SELECT * FROM orders")
List<Order> loadAllOrders();

//	2、查询接口实现
@Override
  public List<Order> loadAllOrders() {
    final String _sql = "SELECT * FROM orders";
    final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 0);
    final Cursor _cursor = __db.query(_statement);
    try {
      final int _cursorIndexOfOrderId = _cursor.getColumnIndexOrThrow("order_id");
      final int _cursorIndexOfAddress = _cursor.getColumnIndexOrThrow("address");
      final int _cursorIndexOfOwnerName = _cursor.getColumnIndexOrThrow("owner_name");
      final int _cursorIndexOfOwnerPhone = _cursor.getColumnIndexOrThrow("owner_phone");
      final int _cursorIndexOfStreet = _cursor.getColumnIndexOrThrow("street");
      final int _cursorIndexOfState = _cursor.getColumnIndexOrThrow("state");
      final int _cursorIndexOfCity = _cursor.getColumnIndexOrThrow("city");
      final int _cursorIndexOfPostCode = _cursor.getColumnIndexOrThrow("post_code");
      final List<Order> _result = new ArrayList<Order>(_cursor.getCount());
      while(_cursor.moveToNext()) {
        final Order _item;
        final Order.OwnerAddress _tmpOwnerAddress;
        if (! (_cursor.isNull(_cursorIndexOfStreet) && _cursor.isNull(_cursorIndexOfState) && _cursor.isNull(_cursorIndexOfCity) && _cursor.isNull(_cursorIndexOfPostCode))) {
          _tmpOwnerAddress = new Order.OwnerAddress();
          _tmpOwnerAddress.street = _cursor.getString(_cursorIndexOfStreet);
          _tmpOwnerAddress.state = _cursor.getString(_cursorIndexOfState);
          _tmpOwnerAddress.city = _cursor.getString(_cursorIndexOfCity);
          _tmpOwnerAddress.postCode = _cursor.getInt(_cursorIndexOfPostCode);
        }  else  {
          _tmpOwnerAddress = null;
        }
        _item = new Order();
        _item.orderId = _cursor.getLong(_cursorIndexOfOrderId);
        _item.address = _cursor.getString(_cursorIndexOfAddress);
        _item.ownerName = _cursor.getString(_cursorIndexOfOwnerName);
        _item.ownerPhone = _cursor.getString(_cursorIndexOfOwnerPhone);
        _item.ownerAddress = _tmpOwnerAddress;
        _result.add(_item);
      }
      return _result;
    } finally {
      _cursor.close();
      _statement.release();
    }
  }

//	3、查询接口调用
AppDatabase db = DbManager.getDbInstance();
OrderDao orderDao = db.getOrderDao();
return orderDao.loadAllOrders();

3.4、内嵌实体

如果实体 Order 内部包含地址信息,地址信息分别包含 城市,邮政等信息,可以这样写,使用@Embedded 注解:

static class OwnerAddress {

        public String street;
        public String state;
        public String city;

        @ColumnInfo(name = "post_code")
        public int postCode;
}

@Embedded
public OwnerAddress ownerAddress;

3.5、配合 LiveData

数据查询可以返回 LiveData 数据:

 @Query("SELECT * FROM orders")
 LiveData<List<Order>> loadAllOrderData();

3.6、配合 RxJava

通过 query 查询返回的实体,可以封装成 对应RxJava 的操作符封装对象,例如 Flowable,Maybe 等:

//	接口声明
@Query("SELECT * from orders where order_id = :id LIMIT 1")
Flowable<Order> queryOrderByIdV2(long id);

@Query("SELECT * from orders where order_id = :id LIMIT 1")
Maybe<Order> queryOrderByIdV3(long id);

// 接口调用
private Maybe<Order> queryOrderV3(){
      AppDatabase db = DbManager.getDbInstance();
      OrderDao orderDao = db.getOrderDao();
      return orderDao.queryOrderByIdV3(10001);
}

Maybe<Order> orderMaybe = queryOrderV3();
        orderMaybe.subscribeOn(Schedulers.io())
             .observeOn(Schedulers.newThread())
             .subscribe(new Consumer<Order>() {
                 @Override
                 public void accept(@NonNull Order order) throws Exception {

                 }
});

以上代码Demo 实现:

五、总结

学会使用 Android Architecture Components 提供的组件简化我们的开发,能够使我们开发的应用模块更解耦更稳定,视图与数据持久层分离,以及更好的扩展性与灵活性,


参考致谢:

  1. Architechture
  2. Lifecycle package class
  3. Save data in a local database using Room
  4. Android Room with a View
  5. Google Samples

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