房间: "类型转换器的返回类型无效"

Question

房间: "类型转换器的返回类型无效"

3

我有一个Room数据库，其中包含以下实体：

data class NoteEntity(
    val startRef: BibleRef,
    val endRef: BibleRef,
    val content: String
)

我添加了以下类型转换器，将BibleRef字段存储为整数：

class Converters {
    @TypeConverter
    fun bibleRefToInt(ref: BibleRef?): Int? {
        // performs conversion...
    }

    @TypeConverter
    fun bibleRefFromInt(refInt: Int?): BibleRef? {
        // performs conversion...
    }
}

我遇到了以下构建错误（使用 kapt）：

Invalid return type for a type converter. - Converters.bibleRefFromInt(java.lang.Integer)

BibleRef 是一个简单的 Kotlin 数据类。

data class BibleRef(
    val book: Int,
    val chapter: Int,
    val verse: Int
)

- Matt Robertson

1个回答

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- MikeT · Accepted Answer

您似乎没有包含@TypeConverters注释。

请注意使用复数形式 (定义 TypeConverters 所在的类) 而不是单数形式 (将方法/函数定义为 TypeConverter)。

对于您的情况，应该是：

@TypeConverters(Converters::class)

建议将它编码在具有@Database注释的类中，该注释可以紧接着或者在@Database注释之后，例如：

@TypeConverters(Converters::class)
@Database(entities = [NoteEntity::class], version = 1)

这提供了最广泛的范围。

用于验证上述内容的完整代码：

BibleRef（未更改）

data class BibleRef(
    val book: Int,
    val chapter: Int,
    val verse: Int
)

NoteEntity（参见注释）

@Entity
data class NoteEntity(
    @PrimaryKey
    val id: Long? = null,
    val startRef: BibleRef,
    val endRef: BibleRef,
    val content: String
)

添加id列作为主键，否则会出现错误：error: An entity must have at least 1 field annotated with @PrimaryKey public final class NoteEntity {
添加@Entity注释，否则会出现错误：error: Entity class must be annotated with @Entity public final class NoteEntity {

转换器（请参阅说明）

class Converters {
    @TypeConverter
    fun bibleRefToInt(ref: BibleRef?): Int? {
        return 0
    }

    @TypeConverter
    fun bibleRefFromInt(ref: Int?): BibleRef? {
        return BibleRef(0,0,0)
    }
}

两者都改为返回适当类型的值。

TheDatabase添加，以便对Room代码进行完整编译并生成生成的Java代码。

@TypeConverters(Converters::class)
@Database(entities = [NoteEntity::class], version = 1)
abstract class TheDatabase: RoomDatabase() {
}

请注意，未使用任何@Dao注释的类。

构建日志：

Executing tasks: [:app:assembleDebug] in project E:\AndroidStudioApps\SO70425430KotlinRoomTypeConverterInvalidReturnType

> Task :app:preBuild UP-TO-DATE
> Task :app:preDebugBuild UP-TO-DATE
> Task :app:compileDebugAidl NO-SOURCE
> Task :app:compileDebugRenderscript NO-SOURCE
> Task :app:generateDebugBuildConfig UP-TO-DATE
> Task :app:checkDebugAarMetadata UP-TO-DATE
> Task :app:generateDebugResValues UP-TO-DATE
> Task :app:generateDebugResources UP-TO-DATE
> Task :app:mergeDebugResources UP-TO-DATE
> Task :app:createDebugCompatibleScreenManifests UP-TO-DATE
> Task :app:extractDeepLinksDebug UP-TO-DATE
> Task :app:processDebugMainManifest UP-TO-DATE
> Task :app:processDebugManifest UP-TO-DATE
> Task :app:processDebugManifestForPackage UP-TO-DATE
> Task :app:processDebugResources UP-TO-DATE
> Task :app:kaptGenerateStubsDebugKotlin
> Task :app:javaPreCompileDebug UP-TO-DATE
> Task :app:mergeDebugNativeDebugMetadata NO-SOURCE
> Task :app:mergeDebugShaders UP-TO-DATE
> Task :app:compileDebugShaders NO-SOURCE
> Task :app:generateDebugAssets UP-TO-DATE
> Task :app:mergeDebugAssets UP-TO-DATE
> Task :app:compressDebugAssets UP-TO-DATE
> Task :app:processDebugJavaRes NO-SOURCE
> Task :app:checkDebugDuplicateClasses UP-TO-DATE
> Task :app:desugarDebugFileDependencies UP-TO-DATE
> Task :app:mergeExtDexDebug UP-TO-DATE
> Task :app:mergeLibDexDebug UP-TO-DATE
> Task :app:mergeDebugJniLibFolders UP-TO-DATE
> Task :app:mergeDebugNativeLibs NO-SOURCE
> Task :app:stripDebugDebugSymbols NO-SOURCE
> Task :app:validateSigningDebug UP-TO-DATE
> Task :app:writeDebugAppMetadata UP-TO-DATE
> Task :app:writeDebugSigningConfigVersions UP-TO-DATE

> Task :app:kaptDebugKotlin
E:\AndroidStudioApps\SO70425430KotlinRoomTypeConverterInvalidReturnType\app\build\tmp\kapt3\stubs\debug\a\a\so70425430kotlinroomtypeconverterinvalidreturntype\TheDatabase.java:8: 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 TheDatabase extends androidx.room.RoomDatabase {
                ^

> Task :app:compileDebugKotlin
w: E:\AndroidStudioApps\SO70425430KotlinRoomTypeConverterInvalidReturnType\app\src\main\java\a\a\so70425430kotlinroomtypeconverterinvalidreturntype\Converters.kt: (9, 23): Parameter 'ref' is never used
w: E:\AndroidStudioApps\SO70425430KotlinRoomTypeConverterInvalidReturnType\app\src\main\java\a\a\so70425430kotlinroomtypeconverterinvalidreturntype\Converters.kt: (14, 25): Parameter 'ref' is never used

> Task :app:compileDebugJavaWithJavac
> Task :app:compileDebugSources
> Task :app:mergeDebugJavaResource UP-TO-DATE
> Task :app:dexBuilderDebug
> Task :app:mergeProjectDexDebug
> Task :app:packageDebug
> Task :app:assembleDebug

Deprecated Gradle features were used in this build, making it incompatible with Gradle 8.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/7.0.2/userguide/command_line_interface.html#sec:command_line_warnings

BUILD SUCCESSFUL in 2s
30 actionable tasks: 7 executed, 23 up-to-date

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