无法为类 ConversionRates 调用无参数构造函数

Question

我有一个货币转换器 Android 应用程序。我正在使用改造从 API 获取费率但就我而言，我的应用程序无法从 api 获取数据并返回该异常

无法为类 package name.ConversionRates 调用无参数构造函数。为此类型向 Gson 注册 InstanceCreator 可能会解决此问题。

ConversionRates 数据类：

data class ConversionRates(
val AED: Double,
val AFN: Double,
val ALL: Double,
val AMD: Double,
val ANG: Double,
val AOA: Double,
val ARS: Double,
val AUD: Double,
val AWG: Double,
val AZN: Double,
val BAM: Double,
val BBD: Double,
val BDT: Double,
val BGN: Double,
val BHD: Double,
val BIF: Double,
val BMD: Double,
val BND: Double,
val BOB: Double,
val BRL: Double,
val BSD: Double,
val BTN: Double,
val BWP: Double,)

视图模型:

@HiltViewModelclass MainViewModel @Inject constructor(
private val repository: MainRepository,
private val dispatchers: DispatcherProvider) : ViewModel(){

sealed class CurrencyEvent {
    class Success(val resultText: String): CurrencyEvent()
    class Failure(val errorText: String): CurrencyEvent()
    object Loading: CurrencyEvent()
    object Empty: CurrencyEvent() }

private val _conversion= MutableStateFlow<CurrencyEvent>(CurrencyEvent.Empty)
val conversion: StateFlow<CurrencyEvent> = _conversion

fun convert(amountStr: String,
    fromCurrency: String,
    toCurrency: String ){

    val fromAmount= amountStr.toFloatOrNull()
    if( fromAmount== null){
        _conversion.value=CurrencyEvent.Failure("Not a valid amount")
        return
    }
    viewModelScope.launch (dispatchers.io){
        _conversion.value= CurrencyEvent.Loading
        when( val ratesResponse= repository.getRates(fromCurrency)) {
            is Resource.Error -> _conversion.value= CurrencyEvent.Failure(ratesResponse.message!!)
            is Resource.Success -> {
                val rates = ratesResponse.data!!.conversion_rates
                val rate = getRateForCurrency(toCurrency, rates)
                if (rate==null){
                    _conversion.value= CurrencyEvent.Failure("Unexpected Error")
                } else {
                    //val convertedCurrency = round(fromAmount * rate * 100)
                    _conversion.value= CurrencyEvent.Success(
                        "$fromAmount $fromCurrency = $toCurrency"
                    )
                }
            }
        }
    }
}
private fun getRateForCurrency(currency: String, rates: ConversionRates) = when (currency) {
    "CAD" -> rates.CAD
    "HKD" -> rates.HKD
    "ISK" -> rates.ISK
    "EUR" -> rates.EUR
    "PHP" -> rates.PHP
    "DKK" -> rates.DKK
    "HUF" -> rates.HUF
    "CZK" -> rates.CZK
    "AUD" -> rates.AUD
    "RON" -> rates.RON
    "SEK" -> rates.SEK
    "IDR" -> rates.IDR
    "INR" -> rates.INR
    "BRL" -> rates.BRL
    "RUB" -> rates.RUB
    "HRK" -> rates.HRK
    "JPY" -> rates.JPY
    "THB" -> rates.THB
    "CHF" -> rates.CHF
    "SGD" -> rates.SGD
    "PLN" -> rates.PLN
    "BGN" -> rates.BGN
    "CNY" -> rates.CNY
    "NOK" -> rates.NOK
    "NZD" -> rates.NZD
    "ZAR" -> rates.ZAR
    "USD" -> rates.USD
    "MXN" -> rates.MXN
    "ILS" -> rates.ILS
    "GBP" -> rates.GBP
    "KRW" -> rates.KRW
    "MYR" -> rates.MYR
    else -> null
}}

货币API

interface CurrencyApi {

@GET("/v6/68c54e50f924117c29176f8f/latest/USD")
suspend fun getRates(
    @Query("base_code") base_code : String
): Response<CurrencyResponse>}

默认主回购

class DefaultMainRepository @Inject constructor(
private val api :CurrencyApi): MainRepository {
override suspend fun getRates(base_code: String): Resource<CurrencyResponse> {

    return try {
        val response = api.getRates(base_code)
        val result= response.body()
        if (response.isSuccessful && result!=null){
            Resource.Success(result)
        } else{
            Resource.Error(response.message())
        }
    }catch (e: Exception) {
        Resource.Error(e.message?: "An error occured")
    }
}}

主要回购：

interface MainRepository {

suspend fun getRates(base_code: String) : Resource<CurrencyResponse>}

Answer 1

显然，kotlin 数据类只能包含大约127 个参数，所以你有两个选择。

1. 将响应数据类分解为两个（费率ATOL和速率MToZ) 并向 API 发出两个请求。

2. 将 JSON 对象 (conversion_rates) 转换为对象列表 Rate(val code: String, val amount: Double) .这可以使用 Moshi 自定义适配器来完成。

   在此处查看代码要点Custom Moshi adapter GitHub 上的完整项目fxConverter

   class MoshiJsonAdapter : JsonAdapter<InfoAndRatesResponse>() {
   
       @FromJson
       override fun fromJson(reader: JsonReader): InfoAndRatesResponse {
   
       reader.beginObject()
   
       var result = ""
       var timeLastUpdateUnix = 0
       var timeLastUpdateUtc = ""
       var timeNextUpdateUnix = 0
       var timeNextUpdateUtc = ""
       var baseCode = ""
       val rates = mutableListOf<Rate>()
   
       while (reader.hasNext()) {
           when (reader.nextName()) {
               "result" -> result = reader.nextString()
               "time_last_update_unix" -> timeLastUpdateUnix = reader.nextInt()
               "time_last_update_utc" -> timeLastUpdateUtc = reader.nextString()
               "time_next_update_unix" -> timeNextUpdateUnix = reader.nextInt()
               "time_next_update_utc" -> timeNextUpdateUtc = reader.nextString()
               "base_code" -> baseCode = reader.nextString()
               "conversion_rates" -> {
   
                   reader.beginObject()
   
                   while (reader.peek() != JsonReader.Token.END_OBJECT) {
   
                       val code = reader.nextName()
   
                       val amount = when (code) {
                           baseCode -> reader.nextInt().toDouble()
                           else -> reader.nextDouble()
                       }
   
                       val infoBaseCode = baseCode
   
                       Timber.tag("MyTag")
                           .d(" code $code amount $amount infoBaseCode $infoBaseCode")
   
                       rates.add(
                           Rate(
                               code = code,
                               amount = amount,
                               infoBaseCode = infoBaseCode,
                           )
                       )
                   }
                   reader.endObject()
               }
               else -> reader.skipValue()
           }
       }
       reader.endObject()
   
       return InfoAndRatesResponse(
           result = result,
           timeLastUpdateUnix = timeLastUpdateUnix,
           timeLastUpdateUtc = timeLastUpdateUtc,
           timeNextUpdateUnix = timeNextUpdateUnix,
           timeNextUpdateUtc = timeNextUpdateUtc,
           baseCode = baseCode,
           rates = rates
        )
       }
   
      @ToJson
       override fun toJson(writer: JsonWriter, value: 
       InfoAndRatesResponse?) {
       throw UnsupportedOperationException()
       }
      }
   

Answer 2

我对此不确定，但是当它说“无法调用无参数构造函数”时，对我来说，这听起来像是您需要能够创建不带参数的 CurrencyResponse 实例。也许尝试设置一些默认值？我会试一试：

data class ConversionRates(
    val AED: Double = 0.0,
    val AFN: Double = 0.0,
    val ALL: Double = 0.0,
    val AMD: Double = 0.0,
    val ANG: Double = 0.0,
    val AOA: Double = 0.0,
    val ARS: Double = 0.0,
    val AUD: Double = 0.0,
    val AWG: Double = 0.0,
    val AZN: Double = 0.0,
    val BAM: Double = 0.0,
    val BBD: Double = 0.0,
    val BDT: Double = 0.0,
    val BGN: Double = 0.0,
    val BHD: Double = 0.0,
    val BIF: Double = 0.0,
    val BMD: Double = 0.0,
    val BND: Double = 0.0,
    val BOB: Double = 0.0,
    val BRL: Double = 0.0,
    val BSD: Double = 0.0,
    val BTN: Double = 0.0,
    val BWP: Double = 0.0,
)