android - Android Kotlin Room Repository 无法从详细活动中检索行
问题描述
我真的在为此苦苦挣扎,希望能得到一些帮助。I'm learning Android Kotlin & building an app that displays a list of walking routes (downloaded from the cloud) in a RecyclerView &, when a route is selected I want to display all details of the route - a simple Master-Detail app. 因为,我正在学习,我也想尝试使用最佳实践。使用 Room 数据库和存储库,我的大部分工作都可以正常工作。数据库已正确填充,并且 RecyclerView 显示路线列表。选择路线后routeID
,其他详细信息将正确传递给活动(TwalksRouteActivity.kt)
以显示详细信息,并且效果很好。
但是,我需要使用 routeID 从数据库(存储库?)中查找路由,因此所有详细信息都可以在详细信息活动中使用,但我无法使其正常工作。我不想传递捆绑包中的所有详细信息,因为一旦这工作正常,我将需要从详细信息活动中进行其他数据库查找。我已经尝试了围绕 Coroutines 的各种解决方案以避免线程阻塞,但完全失败了。所以我的问题是,如何从详细活动中正确地从我的数据库/存储库中获取一行。
这是详细活动(TwalksRouteActivity.kt):
package com.example.android.twalks.ui
import android.os.Bundle
import android.util.Log
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import com.example.android.twalks.R
import com.example.android.twalks.database.RouteDao
import com.example.android.twalks.database.getDatabase
import com.example.android.twalks.domain.Route
import com.example.android.twalks.repository.RoutesRepository
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext
import timber.log.Timber
import timber.log.Timber.*
class TwalksRouteActivity() : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
var bundle: Bundle? = intent.extras
var routeID = bundle?.getInt("routeID")
var routeName = bundle?.getString("routeName")
var routeCategoryName = bundle?.getString("routeCategoryName")
var routeDistance = bundle?.getString("routeDistance")
var routeTime = bundle?.getString("routeTime")
var routeImageFile = bundle?.getString("routeImageFile")
GlobalScope.launch (Dispatchers.Main) {
val database = getDatabase(application)
val routesRepository = RoutesRepository(database)
val selectedRoute = routesRepository.getRoute(routeID)
Log.d("CWM", selectedRoute.toString())
}
setContentView(R.layout.route_detail)
val routeName_Text: TextView = findViewById(R.id.routeName_text)
routeName_Text.text = routeName.toString()
val routeID_Text: TextView = findViewById(R.id.routeID)
routeID_Text.text = routeID.toString()
//Toast.makeText(this,"Here in TwalksRouteActivity", Toast.LENGTH_LONG).show()
//Toast.makeText(applicationContext,routeName,Toast.LENGTH_LONG)
}
}
package com.example.android.twalks.database
import androidx.room.Entity
import androidx.room.PrimaryKey
import com.example.android.twalks.domain.Route
/**
* DataTransferObjects go in this file. These are responsible for parsing responses from the server
* or formatting objects to send to the server. You should convert these to domain objects before
* using them.
*/
@Entity
data class DatabaseRoute constructor(
@PrimaryKey
val routeID: String,
val routeName: String,
val routeImageFile: String,
val routeCategoryName: String,
val routeCategory: String,
val routeDistance: String,
val routeTime: String,
val routeStatus:String)
fun List<DatabaseRoute>.asDomainModel(): List<Route> {
return map {
Route(
routeID = it.routeID,
routeName = it.routeName,
routeImageFile = it.routeImageFile,
routeCategoryName = it.routeCategoryName,
routeCategory = it.routeCategory,
routeDistance = it.routeDistance,
routeTime = it.routeTime,
routeStatus = it.routeStatus)
}
}
房间.kt
package com.example.android.twalks.database
import android.content.Context
import androidx.lifecycle.LiveData
import androidx.room.*
import com.example.android.twalks.domain.Route
@Dao
interface RouteDao {
@Query("select * from databaseroute")
fun getRoutes(): LiveData<List<DatabaseRoute>>
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insertAll(vararg routes: DatabaseRoute)
@Query("select * from databaseroute where routeID = :routeID")
fun getRoute(routeID: Int?): LiveData<Route>
}
@Database(entities = [DatabaseRoute::class],version = 1)
abstract class RoutesDatabase: RoomDatabase() {
abstract val routeDao: RouteDao
}
private lateinit var INSTANCE: RoutesDatabase
fun getDatabase(context: Context): RoutesDatabase {
synchronized(RoutesDatabase::class.java) {
if (!::INSTANCE.isInitialized) {
INSTANCE = Room.databaseBuilder(context.applicationContext,
RoutesDatabase::class.java,
"routes").build()
}
}
return INSTANCE
}
package com.example.android.twalks.domain
/**
* Domain objects are plain Kotlin data classes that represent the things in our app. These are the
* objects that should be displayed on screen, or manipulated by the app.
*
* @see database for objects that are mapped to the database
* @see network for objects that parse or prepare network calls
*/
data class Route(val routeID: String,
val routeName: String,
val routeImageFile: String,
val routeCategoryName: String,
val routeCategory: String,
val routeDistance: String,
val routeTime: String,
val routeStatus: String)
package com.example.android.twalks.network
import android.os.Parcelable
import com.example.android.twalks.database.DatabaseRoute
import com.example.android.twalks.domain.Route
import com.squareup.moshi.JsonClass
import kotlinx.android.parcel.Parcelize
@JsonClass(generateAdapter = true)
data class NetworkRouteContainer(val routes: List<NetworkRoute>)
@JsonClass(generateAdapter = true)
data class NetworkRoute(
val routeID: String,
val routeName: String,
val routeImageFile: String,
val routeCategoryName: String,
val routeCategory: String,
val routeDistance: String,
val routeTime: String,
val routeStatus: String )
/**
* Convert Network results to com.example.android.twalks.database objects
*/
fun NetworkRouteContainer.asDomainModel(): List<Route> {
return routes.map {
Route(
routeID = it.routeID,
routeName = it.routeName,
routeImageFile = it.routeImageFile,
routeCategoryName = it.routeCategoryName,
routeCategory = it.routeCategory,
routeDistance = it.routeDistance,
routeTime = it.routeTime,
routeStatus = it.routeStatus)
}
}
fun NetworkRouteContainer.asDatabaseModel(): Array<DatabaseRoute> {
return routes.map {
DatabaseRoute(
routeID = it.routeID,
routeName = it.routeName,
routeImageFile = it.routeImageFile,
routeCategoryName = it.routeCategoryName,
routeCategory = it.routeCategory,
routeDistance = it.routeDistance,
routeTime = it.routeTime,
routeStatus = it.routeStatus
)
}.toTypedArray()
}
package com.example.android.twalks.repository
import android.util.Log
import androidx.annotation.WorkerThread
import androidx.lifecycle.LiveData
import androidx.lifecycle.Transformations
import com.example.android.twalks.database.RouteDao
import com.example.android.twalks.database.RoutesDatabase
import com.example.android.twalks.database.asDomainModel
import com.example.android.twalks.domain.Route
import com.example.android.twalks.network.Network
import com.example.android.twalks.network.asDatabaseModel
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.withContext
import timber.log.Timber
/**
* Repository for fetching routes from the network and storing them on disk
*/
class RoutesRepository(private val database: RoutesDatabase) {
val routes: LiveData<List<Route>> =
Transformations.map(database.routeDao.getRoutes()) {
it.asDomainModel()
}
suspend fun refreshRoutes() {
withContext(Dispatchers.IO) {
val routelist = Network.twalks.getRoutes().await()
database.routeDao.insertAll(*routelist.asDatabaseModel())
}
}
suspend fun getRoute(id: Int?) {
withContext(Dispatchers.IO) {
val route: LiveData<Route> = database.routeDao.getRoute(id)
//Log.d("CWM2",route.toString())
return@withContext route
}
}
}
解决方案
您的代码不起作用,因为您没有从课堂上返回任何getRoute
内容RoutesRepository
。指定返回类型,您将看到它。
您可以通过返回withContext
块来解决它,但我想建议您进行一些更改,因为您说您正在学习并且还想尝试应用最佳实践。
路道
Room 从 2.1 版本开始支持协程。您所要做的就是用关键字标记您的 DAO 方法suspend
。您不必担心suspend
在 Main 线程上调用 DAO 方法,因为它被挂起并且 Room 设法在后台线程上执行查询。
- 在此处了解有关此主题的更多信息。
所以你的getRoute
DAO 方法看起来像这样:
@Query("select * from databaseroute where routeID = :routeID")
suspend fun getRoute(routeID: Int): Route
注意 1:我将返回类型从更改为LiveData<Route>
,Route
因为我假设您不希望它更改。
注意 2:我没有看到将 nullablerouteID
作为参数的意义,所以我删除了?
.
路由存储库
通过之前的更改getRoute
,您的RoutesRepository
班级方法将如下所示:
suspend fun getRoute(id: Int) = database.routeDao.getRoute(id)
注意 1:正如我之前提到的,你不必担心移动到后台线程,因为 Room 会为你做这件事。
注 2:同样,不可为空的参数。
TwalksRouteActivity
您直接从您的活动中调用您的存储库。我不确定您正在应用的架构,但我希望在中间看到 Presenter 或 ViewModel。GlobalScope
忽略这个细节,我建议你几乎总是避免启动协程。GlobalScope
仅当您知道如何GlobalScope
工作并且完全确定自己在做什么时才使用。
- 在此处了解有关此主题的更多信息。
而不是GlobalScope
你可以使用lifecycleScope
which 在主线程上运行并且它是生命周期感知的。
将您更改GlobalScope.launch {...}
为:
lifecycleScope.launch {
...
val selectedRoute = routesRepository.getRoute(routeID)
//Do something with selectedRoute here
}
注1:您需要androidx.lifecycle:lifecycle-runtime-ktx:2.2.0
或更高。
注意 2:如果您在请求中获取所有 Route 数据,则只能将其传递routeID
给您的新活动。
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