我的app数据库类
@Database(entities = {Detail.class}, version = Constant.DATABASE_VERSION)
public abstract class AppDatabase extends RoomDatabase {
private static AppDatabase INSTANCE;
public abstract FavoritesDao favoritesDao();
public static AppDatabase getAppDatabase(Context context) {
if (INSTANCE == null) {
INSTANCE =
Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, Constant.DATABASE).allowMainThreadQueries().build();
//Room.inMemoryDatabaseBuilder(context.getApplicationContext(),AppDatabase.class).allowMainThreadQueries().build();
}
return INSTANCE;
}
public static void destroyInstance() {
INSTANCE = null;
}
}
Gradle自由:
compile "android.arch.persistence.room:runtime:+"
annotationProcessor "android.arch.persistence.room:compiler:+"
当我请求实例时，它会给出这个错误，AppDatabase_Impl不存在
在我的应用课上
public class APp extends Application {
private boolean appRunning = false;
@Override
public void onCreate() {
super.onCreate();
AppDatabase.getAppDatabase(this); //--AppDatabase_Impl does not exist
}
}
使用下面的gradle链接:
compile 'android.arch.persistence.room:runtime:1.0.0-alpha9'
annotationProcessor 'android.arch.persistence.room:compiler:1.0.0-alpha9'
你需要创建一个不同的单例类，并从那里获取AppDatabase，如下所示:
RoomDB.java
public class RoomDB {
private static RoomDB INSTANCE;
public static AppDatabase getInstance(Context context) {
if (INSTANCE == null) {
INSTANCE =
Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, Constant.DATABASE).allowMainThreadQueries().build();
//Room.inMemoryDatabaseBuilder(context.getApplicationContext(),AppDatabase.class).allowMainThreadQueries().build();
}
return INSTANCE;
}
public static void destroyInstance() {
INSTANCE = null;
}
App.java
public class App extends Application {
private boolean appRunning = false;
@Override
public void onCreate() {
super.onCreate();
RoomDB.getInstance(this); //This will provide AppDatabase Instance
}
如果你正在使用kotlin，将kotlin注释处理器插件添加到应用级别build.gradle
plugins {
id "org.jetbrains.kotlin.kapt"
}
还要删除annotationProcessor并将其替换为kapt
而不是
dependencies {
def room_version = "2.3.0"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
}
使用
dependencies {
def room_version = "2.3.0"
implementation "androidx.room:room-runtime:$room_version"
kapt "androidx.room:room-compiler:$room_version"
}
注释处理器只能在java环境中工作。kapt同时负责java和kotlin。如果你的实现有问题，这些插件会在编译时显示出来。
对我来说，只要你包含任何与Room数据库相关的导入，Android Studio就会自动更新依赖项。但根据https://developer.android.com/jetpack/androidx/releases/room#declaring_dependencies，你需要更新一些。下面是我的代码库的样子:
AppDatabase.kt
import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
@Database(entities = arrayOf(MyEntity::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun myDAO(): MyDAO
companion object {
@Volatile private var instance: AppDatabase? = null
private val LOCK = Any()
operator fun invoke(context: Context)= instance ?: synchronized(LOCK){
instance ?: buildDatabase(context).also { instance = it}
}
private fun buildDatabase(context: Context) = Room.databaseBuilder(context,
AppDatabase::class.java, "db-name.db")
.build()
}
}
更新构建。Gradle在其中一个答案中指定:
apply plugin: 'kotlin-kapt' // this goes with other declared plugin at top
dependencies { // add/update the following in dependencies section
implementation 'androidx.room:room-runtime:2.2.3'
// annotationProcessor 'androidx.room:room-compiler:2.2.3' // remove this and use the following
kapt "androidx.room:room-compiler:2.2.3"
}
同步gradle，你应该可以开始了。
