如何在 Kotlin [Dagger-Hilt] 中创建和使用房间数据库
How to create and use a Room Database in Kotlin [Dagger-Hilt]
这是一个自我回答的问题,我本来打算早些时候问的,因为我在我的项目中遇到了代表曝光问题,但经过几个小时的研究后最终解决了它。我没有保持沉默,而是认为这可能会对将来的某个人有所帮助。本教程演示了如何创建 Room 数据库并在 activity/fragment 中使用它。此处给出的示例用例是查询数据库的大小并更新片段中的视图。
注意:后面的代码中有一些 Dagger-Hilt 依赖项注入,但如果您手动执行自己的依赖项注入,则应采用相同的方法。我还希望您对 MVVM 架构有一些基本了解。如果您对涉及 LiveData 的其他方式感兴趣,您可能会在这里找到有用的 Java 相关问题:resource 1, ;但是,重点是 Kotlin,此解决方案不需要 LiveData。
无论项目包的结构如何,您都必须关联项目中的 kotlin 文件,但导入应保持不变。在这种情况下,我使用 Dagger-Hilt 进行依赖项注入以避免样板代码。
ItemsYouAreStoringInDB.kt
import androidx.room.Entity
import androidx.room.PrimaryKey
@Entity(tableName = "items")
data class ItemsYouAreStoringInDB(/*Parameter of Item entry*/) {
@PrimaryKey(autoGenerate = true)
var id: Int? = null
}
YourDao.kt
import androidx.room.*
@Dao
interface YourDAO {
// Other insertion/deletion/query operations
@Query("SELECT count(id) FROM items") // items is the table in the @Entity tag of ItemsYouAreStoringInDB.kt, id is a primary key which ensures each entry in DB is unique
suspend fun numberOfItemsInDB() : Int // suspend keyword to run in coroutine
}
YourDatabase.kt
import androidx.room.Database
import androidx.room.RoomDatabase
@Database(
entities = [ItemsYouAreStoringInDB::class], // Tell the database the entries will hold data of this type
version = 1
)
abstract class YourDatabase : RoomDatabase() {
abstract fun getYourDao(): YourDAO
}
使用 Dagger-Hilt 进行依赖注入,可以创建 YourRepository,因为 Dagger-Hilt 会在幕后做一些事情,通过 YourDatabase 的抽象 fun getYourDao() 提供 notificationDao
YourRepository.kt
import path.to.ItemsYouAreStoringInDB
import path.to.YourDAO
import javax.inject.Inject // Dagger-Hilt to allow @Inject constructor
class YourRepository @Inject constructor(
private val yourDAO: YourDAO
){
// Other functions from YourDao.kt
suspend fun numberOfItemsInDB() = yourDAO.numberOfItemsInDB()
}
这不是关于如何使用 Dagger-Hilt 的演示,但需要以下两个文件:
AppModule.kt
import android.content.Context
import androidx.room.Room
import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import dagger.hilt.android.qualifiers.ApplicationContext
import path.to.YourDatabase
import javax.inject.Singleton
@Module
@InstallIn(SingletonComponent::class)
object AppModule {
@Singleton // Tell Dagger-Hilt to create a singleton accessible everywhere in ApplicationCompenent (i.e. everywhere in the application)
@Provides
fun provideYourDatabase(
@ApplicationContext app: Context
) = Room.databaseBuilder(
app,
YourDatabase::class.java,
"your_db_name"
).build() // The reason we can construct a database for the repo
@Singleton
@Provides
fun provideYourDao(db: YourDatabase) = db.getYourDao() // The reason we can implement a Dao for the database
BaseApplication.kt
import android.app.Application
import dagger.hilt.android.HiltAndroidApp
@HiltAndroidApp
class BaseApplication : Application() {}
您还需要更新 AndroidManifest 文件和 select BaseApplication 作为应用程序入口点 <application android:name="path.to.BaseApplication" ...
以允许 Android 利用 Dagger-刀柄。
继续...
YourViewModel.kt
import dagger.hilt.android.lifecycle.HiltViewModel
import androidx.lifecycle.ViewModel
import path.to.YourRepository
@HiltViewModel
class MainViewModel @Inject constructor(
private val repository: YourRepository
): ViewModel() {
suspend fun databaseSize() : Int {
return repository.numberOfItemsInDB()
}
}
现在您的视图模型可以作为一个单例创建并可在整个应用程序中访问(不能存在两个实例),您可以在 Fragment/Activity 中使用它。 viewmodel 可以访问存储库,该存储库可以通过查询 Room 数据库接收信息。这是您如何在片段中使用它的示例:
YourFragment.kt
@AndroidEntryPoint // Dagger-Hilt requirement
class YourFragment : Fragment(R.layout.fragment_yourFragmentName) {
private val viewModel: MainViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setViewsBasedOnRepo() // You might want to call this in onResume()
}
private fun setViewsBasedOnRepo() {
GlobalScope.launch(Dispatchers.Main) { // Dispatchers.Main because only the Main thread can touch UI elements. Otherwise you may wish to use Dispatchers.IO instead!
val size =
withContext(Dispatchers.Default) { viewModel.databaseSize() }
if (size == 0) { // Do stuff based on an empty database
btnAddItemsToDB.visibility = View.VISIBLE
textViewWarnNoItemsInDB.visibility = View.VISIBLE
recyclerViewItems.visibility = View.INVISIBLE
} else { // Do other stuff when database has entries of type ItemsYouAreStoringInDB
btnAddItemsToDB.visibility = View.INVISIBLE
textViewWarnNoItemsInDB.visibility = View.INVISIBLE
rvNotifications.visibility = View.VISIBLE
}
}
}
}
这是一个自我回答的问题,我本来打算早些时候问的,因为我在我的项目中遇到了代表曝光问题,但经过几个小时的研究后最终解决了它。我没有保持沉默,而是认为这可能会对将来的某个人有所帮助。本教程演示了如何创建 Room 数据库并在 activity/fragment 中使用它。此处给出的示例用例是查询数据库的大小并更新片段中的视图。
注意:后面的代码中有一些 Dagger-Hilt 依赖项注入,但如果您手动执行自己的依赖项注入,则应采用相同的方法。我还希望您对 MVVM 架构有一些基本了解。如果您对涉及 LiveData 的其他方式感兴趣,您可能会在这里找到有用的 Java 相关问题:resource 1,
无论项目包的结构如何,您都必须关联项目中的 kotlin 文件,但导入应保持不变。在这种情况下,我使用 Dagger-Hilt 进行依赖项注入以避免样板代码。
ItemsYouAreStoringInDB.kt
import androidx.room.Entity
import androidx.room.PrimaryKey
@Entity(tableName = "items")
data class ItemsYouAreStoringInDB(/*Parameter of Item entry*/) {
@PrimaryKey(autoGenerate = true)
var id: Int? = null
}
YourDao.kt
import androidx.room.*
@Dao
interface YourDAO {
// Other insertion/deletion/query operations
@Query("SELECT count(id) FROM items") // items is the table in the @Entity tag of ItemsYouAreStoringInDB.kt, id is a primary key which ensures each entry in DB is unique
suspend fun numberOfItemsInDB() : Int // suspend keyword to run in coroutine
}
YourDatabase.kt
import androidx.room.Database
import androidx.room.RoomDatabase
@Database(
entities = [ItemsYouAreStoringInDB::class], // Tell the database the entries will hold data of this type
version = 1
)
abstract class YourDatabase : RoomDatabase() {
abstract fun getYourDao(): YourDAO
}
使用 Dagger-Hilt 进行依赖注入,可以创建 YourRepository,因为 Dagger-Hilt 会在幕后做一些事情,通过 YourDatabase 的抽象 fun getYourDao() 提供 notificationDao YourRepository.kt
import path.to.ItemsYouAreStoringInDB
import path.to.YourDAO
import javax.inject.Inject // Dagger-Hilt to allow @Inject constructor
class YourRepository @Inject constructor(
private val yourDAO: YourDAO
){
// Other functions from YourDao.kt
suspend fun numberOfItemsInDB() = yourDAO.numberOfItemsInDB()
}
这不是关于如何使用 Dagger-Hilt 的演示,但需要以下两个文件:
AppModule.kt
import android.content.Context
import androidx.room.Room
import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import dagger.hilt.android.qualifiers.ApplicationContext
import path.to.YourDatabase
import javax.inject.Singleton
@Module
@InstallIn(SingletonComponent::class)
object AppModule {
@Singleton // Tell Dagger-Hilt to create a singleton accessible everywhere in ApplicationCompenent (i.e. everywhere in the application)
@Provides
fun provideYourDatabase(
@ApplicationContext app: Context
) = Room.databaseBuilder(
app,
YourDatabase::class.java,
"your_db_name"
).build() // The reason we can construct a database for the repo
@Singleton
@Provides
fun provideYourDao(db: YourDatabase) = db.getYourDao() // The reason we can implement a Dao for the database
BaseApplication.kt
import android.app.Application
import dagger.hilt.android.HiltAndroidApp
@HiltAndroidApp
class BaseApplication : Application() {}
您还需要更新 AndroidManifest 文件和 select BaseApplication 作为应用程序入口点 <application android:name="path.to.BaseApplication" ...
以允许 Android 利用 Dagger-刀柄。
继续...
YourViewModel.kt
import dagger.hilt.android.lifecycle.HiltViewModel
import androidx.lifecycle.ViewModel
import path.to.YourRepository
@HiltViewModel
class MainViewModel @Inject constructor(
private val repository: YourRepository
): ViewModel() {
suspend fun databaseSize() : Int {
return repository.numberOfItemsInDB()
}
}
现在您的视图模型可以作为一个单例创建并可在整个应用程序中访问(不能存在两个实例),您可以在 Fragment/Activity 中使用它。 viewmodel 可以访问存储库,该存储库可以通过查询 Room 数据库接收信息。这是您如何在片段中使用它的示例:
YourFragment.kt
@AndroidEntryPoint // Dagger-Hilt requirement
class YourFragment : Fragment(R.layout.fragment_yourFragmentName) {
private val viewModel: MainViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setViewsBasedOnRepo() // You might want to call this in onResume()
}
private fun setViewsBasedOnRepo() {
GlobalScope.launch(Dispatchers.Main) { // Dispatchers.Main because only the Main thread can touch UI elements. Otherwise you may wish to use Dispatchers.IO instead!
val size =
withContext(Dispatchers.Default) { viewModel.databaseSize() }
if (size == 0) { // Do stuff based on an empty database
btnAddItemsToDB.visibility = View.VISIBLE
textViewWarnNoItemsInDB.visibility = View.VISIBLE
recyclerViewItems.visibility = View.INVISIBLE
} else { // Do other stuff when database has entries of type ItemsYouAreStoringInDB
btnAddItemsToDB.visibility = View.INVISIBLE
textViewWarnNoItemsInDB.visibility = View.INVISIBLE
rvNotifications.visibility = View.VISIBLE
}
}
}
}