Android Room Database：添加 TypeConverter 以存储对象列表后插入时崩溃答案

【问题标题】：Android Room Database: crashing on insert after adding TypeConverter to store list of objectsAndroid Room Database：添加 TypeConverter 以存储对象列表后插入时崩溃
【发布时间】：2022-01-16 14:26:56
【问题描述】：

我没有收到任何错误，但在调试期间我的应用程序在此行崩溃：

 currentWeatherDao.insertWeatherData(currentWeather)

在哪里

currentWeather = CurrentWeatherEntry(base=stations, clouds=Clouds(all=19), cod=200, coordinate=Coordinate(lat=50.0833, lon=19.9167), dt=1639359545, id=3094802, main=Main(feelsLike=-10.06, humidity=93, pressure=1023, temp=-4.69, tempMax=-0.63, tempMin=-6.89), name=Krakow, sys=Sys(country=PL, id=19912, message=0.0, sunrise=1639377067, sunset=1639406289, type=2), timezone=3600, visibility=2500, weather=[Weather(description=mist)], wind=Wind(deg=70, speed=4.02))

在我开始实施 TypeConverter 以在我的数据库中存储对象列表之前一切正常，现在应用程序在插入时崩溃，我找不到代码问题。

这里是相关代码。

实体：

const val CURRENT_WEATHER_ID = 0


@Entity(tableName = "current_weather")
data class CurrentWeatherEntry(
val base: String,
@Embedded(prefix = "clouds_")
val clouds: Clouds,
val cod: Int,
@SerializedName("coord")
@Embedded(prefix = "coordinate_")
val coordinate: Coordinate,
val dt: Int,
val id: Int,
@Embedded(prefix = "main_")
val main: Main,
val name: String,
@Embedded(prefix = "sys_")
val sys: Sys,
val timezone: Int,
val visibility: Int,
val weather: List<Weather>,
@Embedded(prefix = "wind_")
val wind: Wind
) {

@PrimaryKey(autoGenerate = false)
var keyId: Int = CURRENT_WEATHER_ID

constructor() :this("", Clouds(0), 0, Coordinate(0.0,0.0), 0, 0,
    Main(0.0,0,0,0.0,0.0,0.0),
    "",Sys("",0,0.0,0,0,0),0,
    0, mutableListOf(Weather("")),Wind(0,0.0))
}

数据库：

@Database(

entities = [CurrentWeatherEntry::class],
version = 1
)

@TypeConverters(Converters::class)
abstract class ForecastDatabase: RoomDatabase() {

abstract fun getCurrentWeatherDao() : CurrentWeatherDao

companion object {
    @Volatile private var instance: ForecastDatabase? = null
    private val STOP = Any()

    operator fun invoke(context: Context) = instance ?: synchronized(STOP){
        instance ?: createDatabase(context).also{instance = it}
    }

    private fun createDatabase(context: Context) = 
Room.databaseBuilder(context.applicationContext,
    ForecastDatabase::class.java, "forecast.db")
        .build()

}

}

道：

@Dao
interface CurrentWeatherDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insertWeatherData(weatherEntry:CurrentWeatherEntry)

@Query("select * from current_weather where keyId = $CURRENT_WEATHER_ID")
fun readWeatherData(): LiveData<CurrentWeatherEntry>

}

转换器：

class Converters {

@TypeConverter
fun fromListWeatherToString(weatherList: List<Weather>):String
{
    return Gson().toJson(weatherList)
}

@TypeConverter
fun fromStringToWeatherList(weatherString: String):List<Weather>
{
    val listType: Type = object : TypeToken<List<Weather>>() {}.type

    return Gson().fromJson(weatherString,listType)
}

【问题讨论】：

在您的 Converters 类中使用 ArrayList 而不是 List。
尝试了 ArrayList 和 MutableList，应用在插入时仍然崩溃。

标签： android kotlin mvvm android-room

【解决方案1】：

您的列不能是 List/Array 对象。

您可以做的是将列作为对象，将列表/数组作为成员/字段。

例如

data class WeatherListHolder(
   val weatherList: List<Weather>
)

然后将实体中的列设置为

val weather: WeatherListHolder,

显然您需要相应地更改构造函数和类型转换器。

【讨论】：

您好，我已经更改了您的建议，但插入时应用程序仍然崩溃。