使用 Retrofit 和 GsonConverterFactory 将 JsonArray 转换为 Kotlin 数据类（预期为 BEGIN_OBJECT，但实际为 BEGIN_ARRAY）

Question

我正在尝试从github（ https://github.com/JamesFT/Database-Quotes-JSON/blob/master/quotes.json ）加载quotesJson文件。我是改造和所有这些的新手，所以我只是尝试遵循并理解教程（https://android.jlelse.eu/android-networking-in-2019-retrofit-with-kotlins-coroutines-aefe82c4d777）。如果这很愚蠢或者真的很简单，我非常抱歉。我仍在为此苦苦挣扎。如果我能得到一个简短的解释为什么它以其他方式完成，我将不胜感激！

我查看了 Retrofit 的文档，搜索了所有类似的溢出问题。问题是，如果我尝试更改 fun getQuotes(): Deferred<Response<QuoteResponse>> 为， fun getQuotes(): Deferred<ResponseList<Quotes>> 则会出现错误 val quoteResponse = safeApiCall(...

    private val okHttpClient = OkHttpClient().newBuilder()
        .build()

    fun retrofit() : Retrofit = Retrofit.Builder()
        .client(okHttpClient)
        .baseUrl("https://raw.githubusercontent.com/JamesFT/Database-Quotes-JSON/master/")
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(CoroutineCallAdapterFactory())
        .build()


    val quoteApi : QuoteApi = retrofit().create(QuoteApi::class.java)

}

模型

   val quoteAuthor : String,
   val quoteText : String
)

// Data Model for the Response returned from the Api
data class QuoteResponse(
    val results : List<Quote>
)

//A retrofit Network Interface for the Api
interface QuoteApi{
    @GET("quotes.json")
    fun getQuotes(): Deferred<Response<QuoteResponse>>
    // fun getQuotes(): Deferred<Response<QuoteResponse>>
}

val quoteResponse = safeApiCall(
            call = {api.getQuotes().await()}, // i get the error here if i change something myself
            errorMessage = "Error Fetching Popular Movies"
        )

        return quoteResponse?.results?.toMutableList()

    }

suspend fun <T : Any> safeApiCall(call: suspend () -> Response<T>, errorMessage: String): T? {

        val result : Result<T> = safeApiResult(call,errorMessage)
        var data : T? = null

        when(result) {
            is Result.Success ->
                data = result.data
            is Result.Error -> {
                Log.d("1.DataRepository", "$errorMessage & Exception - ${result.exception}")
            }
        }


        return data

    }

    Process: com.example.quoteappmvvm, PID: 7373
    com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $
...

Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $
        at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:385)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:215)```

Answer 1

您面临的问题是因为响应是一个数组，但您试图将其作为对象来处理。

这就是您的 QuoteApi 的样子

interface QuoteApi{
    @GET("quotes.json")
    fun getQuotes(): Deferred<Response<List<Quote>>>
}

说明：为您更好地解释一下 - 您当前的预期响应是

data class QuoteResponse(
    val results : List<Quote>
)

Retrofit 和 Gson 期望您的 JSON 响应看起来像

{
  "results": [...here would be your Qoute objects...]
}

实际上响应只是一个数组

[...here are Quote objects...]

。