【Android】Jetpack全组件实战开发短视频应用App(六)

这一篇我们主要介绍下

Room

Room

Room

sqlite

SQLite

Retrofit

LiveData

LifeCycle

Paging

Room

 implementation "Android.arch.persistence.room:runtime:1.1.1"
 annotationProcessor 'android.arch.persistence.room:compiler:1.1.1'

我们先新建一个类

CacheDatabase

RoomDatabase

public class CacheDatabase extends RoomDatabase {
}

这里我们看见AS提示我们需要实现

RoomDatabase

abstract

Room

annotationProcessor

CacheDatabase

RoomDatabase

public abstract class CacheDatabase extends RoomDatabase {
}

接着我们对我们这个

Database

 //创建一个内存数据库
 //但是这种数据库的数据只存在于内存中，也就是进程被杀之后，数据随之丢失
Room.inMemoryDatabaseBuilder()

这种我们一般不会使用,所以我们一般都是用下面这种方式

 Room.databaseBuilder(AppGlobals.getApplication(), CacheDatabase.class, "joke_video_cache")

我们看下这个方法源码

 
    @SuppressWarnings("WeakerAccess")
    @NonNull
    public static  RoomDatabase.Builder databaseBuilder(
            @NonNull Context context, @NonNull Class klass, @NonNull String name) {
        //noinspection ConstantConditions
        if (name == null || name.trim().length() == 0) {
            throw new IllegalArgumentException("Cannot build a database with null or empty name."
                    + " If you are trying to create an in memory database, use Room"
                    + ".inMemoryDatabaseBuilder");
        }
        return new RoomDatabase.Builder(context, klass, name);
    }

第一个参数是上下文;第二个参数是使用

Database

RoomDatabase

Database

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"
    defaultConfig {
       //......
        javaCompileOptions{
            annotationProcessorOptions{
                arguments=["room.schemaLocation":"$projectDir/schemas".toString()]
            }
        }
    }
 		//......
}

因为我们还没有

Entity

@Entity(tableName = "cache")
public class Cache implements Serializable {
    @PrimaryKey(autoGenerate = false)
    public String key;
    @ColumnInfo(name = "data")
    public byte[] data;
}

这里需要使用

Entity

PrimaryKey

autoGenerate

Room

false

ColumnInfo

key

data

key

data

接着我们回到我们刚才的

CacheDatabase

@Database(entities = {Cache.class},version = 1,exportSchema = true)
public abstract class CacheDatabase extends RoomDatabase {
}

我们通过

Room.databaseBuilder

RoomDatabase.Builder

	 Room.databaseBuilder(AppGlobals.getApplication(), CacheDatabase.class, "joke_video_cache")
                //是否允许在主线程进行查询
                //.allowMainThreadQueries()
                //数据库创建和打开后的回调
                //.addCallback()
                //设置查询的线程池
                //.setQueryExecutor()
                //.openHelperFactory()
                //room的日志模式
                //.setJournalMode()
                //数据库升级异常之后的回滚
                //.fallbackToDestructiveMigration()
                //数据库升级异常后根据指定版本进行回滚
                //.fallbackToDestructiveMigrationFrom()

如果我们需要进行数据库的升级,需要在配置数据库的时候调用

addMigrations

 
        @NonNull
        public Builder addMigrations(@NonNull  Migration... migrations) {
            if (mMigrationStartAndEndVersions == null) {
                mMigrationStartAndEndVersions = new HashSet();
            }
            for (Migration migration: migrations) {
                mMigrationStartAndEndVersions.add(migration.startVersion);
                mMigrationStartAndEndVersions.add(migration.endVersion);
            }
            mMigrationContainer.addMigrations(migrations);
            return this;
        }

入参是多个

Migration

Migration

数据库操作我们需要使用

Dao

CacheDao

BaseDao

CacheDao

BaseDao

@Dao
public interface BaseDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertItem(T item);//插入单条数据
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertItems(List items);//插入list数据
    @Delete
    void deleteItem(T item);//删除item
    @Update(onConflict = OnConflictStrategy.REPLACE)
    void updateItem(T item);//更新item
}

@Dao
public interface CacheDao extends BaseDao{
    //如果是一对多,这里可以写List
    @Query("select *from cache where `key`=:key")
    Cache getCache(String key);
}