在 kotlin 中首次构建 Room 数据库时如何修复异常

Question

我在第一次创建房间数据库时一直遇到这个异常

  java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Package.getName()' on a null object reference

这是我的房间数据库代码：

@Database(entities = [Channel::class], version = 1)
abstract class ChannelRoomDatabase : RoomDatabase() {

    abstract fun channelDao(): ChannelDao

    companion object {
        private var INSTANCE: ChannelRoomDatabase? = null

        fun getInstance(application: Application): ChannelRoomDatabase? {
            if (INSTANCE == null) {

                    INSTANCE = Room.databaseBuilder(application,
                            ChannelRoomDatabase::class.java,
                            "channels")
                            .build()
            }

            return INSTANCE
        }
    }

}

和 gradle 代码：

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'

    def room_version = "1.1.1"

    implementation "android.arch.persistence.room:runtime:$room_version"
    kapt "android.arch.persistence.room:compiler:$room_version"

我在构建项目时也遇到了这个错误：

Execution failed for task ':app:kaptGenerateStubsDebugKotlin'.

Folder /home/Desktop/MySendBird/app/build/generated/source/kaptKotlin/debug


Folder /home/Desktop/MySendBird/app/build/generated/source/kaptKotlin/release


3rd-party Gradle plug-ins may be the cause

可能是什么原因？我在这里看到过类似的问题，但没有任何线索。请帮忙！

更新！在我的 Dao 中我得到这个错误

那么如何让@Query 理解它我给它一个 java String 而不是 Kotlin String

另见堆栈跟踪：

/home/Desktop/MySendBird/app/build/tmp/kapt3/stubs/debug/ChannelRoomDatabase.java:6: warning: Schema export directory is not provided to the annotation processor so we cannot export the schema. You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.
public abstract class ChannelRoomDatabase extends android.arch.persistence.room.RoomDatabase {
                ^
:app:compileDebugKotlin
w: /home/Desktop/MySendBird/app/src/main/java/com/example/anna/mysendbird/repository/ChannelRepository.kt: (16, 13): Variable 'db' is never used
w: /home/Desktop/MySendBird/app/src/main/java/com/example/anna/mysendbird/repository/ChannelRepository.kt: (47, 23): Parameter 'channel' is never used
w: /home/Desktop/MySendBird/app/src/main/java/com/example/anna/mysendbird/view/MainActivity.kt: (179, 29): Parameter 'userId' is never used

查看类似问题：

using Room with kotlin, get exception when build the database

Answer 1

您收到 Android 房间架构目录错误

/home/Desktop/MySendBird/app/build/tmp/kapt3/stubs/debug/ChannelRoomDatabase.java:6: warning: Schema export directory is not provided to the annotation processor so we cannot export the schema. You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.
public abstract class ChannelRoomDatabase extends android.arch.persistence.room.RoomDatabase {

未向注释处理器提供模式导出目录

您需要将架构目录添加到您的 应用的 gradle.build，如下所示，

android {

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

}

这将告诉您的 Room 注释处理器生成数据库架构并将其放在 "room.schemaLocation"

下提到的目录下

在 kotlin 中首次构建 Room 数据库时如何修复异常

How to fix exception when first buliding Room database in kotlin

java

android

kotlin

kotlin-android-extensions

android-room