Room TypeConverter with constructer

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我在风中等你
我在风中等你 2021-02-14 20:27

I have Room TypeConverter and I need to inject parameter to it\'s constructor

class RoomConverters(moshi Moshi) {

    @TypeConverter
    fun fromUs         


        
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4条回答
  • 2021-02-14 21:03

    As of August 11th 2020 there's still no fix for this from Google. Check either of these workarounds in the meantime.

    https://issuetracker.google.com/issues/142086380 https://issuetracker.google.com/issues/121067210

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  • 2021-02-14 21:13

    I use dagger-android, and faced same problem. Solution is when creating AppDatabase

    @Provides @Reusable
    fun provideDatabase(context: Context, moshi: Moshi): AppDatabase = 
        Room.databaseBuilder(...).build().apply { AppDatabase.moshi = moshi }
    

    AppDatabase is simple RoomDatabase:

    @Database(
        entities = [OrderEntity::class],
        version = 1,
        exportSchema = false
    )
    @TypeConverters(DbConverters::class)
    abstract class AppDatabase : RoomDatabase() {
        companion object {
            lateinit var moshi: Moshi
        }
    
        abstract fun orderDao(): OrderDao
    }
    

    Then use this companion object in converter:

    class DbConverters {
    
        @TypeConverter
        fun orderInfoToString(orderInfo: OrderInfo?): String? = 
               AppDatabase.moshi.adapter(OrderInfo::class.java).toJson(orderInfo)
    
        @TypeConverter
        fun stringToOrderInfo(value: String): OrderInfo? = 
              AppDatabase.moshi.adapter(OrderInfo::class.java).fromJson(value)
    }
    

    This is looking ugly, I guess, but works. Maybe using static/companion object with @Reuseable scope is a bad idea. Moshi, though, is provided using @Singleton scope in AppModule, so basically live through entire application life

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  • 2021-02-14 21:17

    I checked documentation even for the newest rc version (2.2.0-rc01) and there is no way to do that. I think it's a joke that we can't register custom TypeConverters in DatabaseBuilder, so I created bug for that on Google issue tracker.

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  • 2021-02-14 21:23

    You can create Room TypeConverter with constructor parameters from version 2.3.0-alpha03

    Release notes:

    Room now has APIs for providing instances of type converters such that the app can control their initialization. To mark a type converter that will be provided to Room use the new annotation @ProvidedTypeConverter

    https://developer.android.com/jetpack/androidx/releases/room#2.3.0-alpha03

    In your case you should add @ProvidedTypeConverter to RoomConverter

    @ProvidedTypeConverter    
    class RoomConverters(moshi: Moshi)
    

    Create converter at db creation time and pass it to database builder:

    val roomConverter = RoomConverters(Moshi())
    val db = Room.databaseBuilder()
             .addTypeConverter(roomConverter)
             .build()
    

    Also you can use DI framework e.g. Dagger2

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