我正在尝试使用 Kotlin 和 Room Persistence Library 编写一个简单的应用程序. 我关注了the tutorial在 Android 持久性代码实验室中。
这是我在 Kotlin 中的 AppDatabase
类:
@Database(entities = arrayOf(User::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userModel(): UserDao
companion object {
private var INSTANCE: AppDatabase? = null
@JvmStatic fun getInMemoryDatabase(context: Context): AppDatabase {
if (INSTANCE == null) {
INSTANCE = Room.inMemoryDatabaseBuilder(context.applicationContext, AppDatabase::class.java).allowMainThreadQueries().build()
}
return INSTANCE!!
}
@JvmStatic fun destroyInstance() {
INSTANCE = null
}
}
}
但是当我尝试运行该应用程序时,它立即崩溃。 这是崩溃日志:
Caused by: java.lang.RuntimeException: cannot find implementation for com.ttp.kotlin.kotlinsample.room.AppDatabase. AppDatabase_Impl does not exist
at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:90)
at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:340)
at com.ttp.kotlin.kotlinsample.room.AppDatabase$Companion.getInMemoryDatabase(AppDatabase.kt:19)
at com.ttp.kotlin.kotlinsample.MainKotlinActivity.onCreate(MainKotlinActivity.kt:28)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
看起来类 AppDatabase_Impl
不是自动生成的。我检查了从codelab下载的原始java应用程序,发现AppDatabase_Impl
是自动生成的。
Kotlin 版本:1.1.2-3
房间版本:1.0.0-alpha1
有没有人有这方面的经验?
编辑:
使用 kapt
解决了我的问题。就我而言,我必须将 annotationProcessor
替换为 kapt
。
最佳答案
通常在项目 build.gradle
我定义依赖版本:
ext {
buildToolsVersion = '25.0.2'
supportLibVersion = '25.3.1'
espressoVersion = '2.2.2'
archRoomVersion = '1.0.0-alpha1'
}
所以在应用程序 build.gradle
中,依赖项看起来像:
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
compile "com.android.support:appcompat-v7:${rootProject.supportLibVersion}"
compile "android.arch.persistence.room:runtime:${rootProject.archRoomVersion}"
annotationProcessor "android.arch.persistence.room:compiler:${rootProject.archRoomVersion}"
kapt "android.arch.persistence.room:compiler:${rootProject.archRoomVersion}"
androidTestCompile("com.android.support.test.espresso:espresso-core:${rootProject.espressoVersion}", {
exclude group: 'com.android.support', module: 'support-annotations'
})
testCompile 'junit:junit:4.12'
}
现在您可以在 Kotlin 中定义实体 Daos 和数据库。
数据库:
@Database(entities = arrayOf(User::class), version = 1)
abstract class Database : RoomDatabase() {
abstract fun userDao(): UserDao
}
实体:
@Entity(tableName = "user")
class User {
@PrimaryKey(autoGenerate = true)
var id: Int = 0
var name: String = ""
}
道:
@Dao
interface UserDao {
@Query("SELECT * FROM user")
fun getAll(): List<User>
@Insert
fun insertAll(vararg users: User)
@Delete
fun delete(user: User)
}
注意:使用参数查询。 Kotlin 重命名参数,因此通过 userId 检索属于用户的所有电子邮件的 SQL 查询是:
@Query("SELECT * FROM email "
+ "INNER JOIN user ON user.id = email.userId "
+ "WHERE user.id = :arg0")
fun getEmailsForUser(userId: Int): List<Email>
关于database - Android Room Persistence 库和 Kotlin,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44065371/