How to solve JSON retrofit error with Deferred Response

Question

I followed with tutorial : https://android.jlelse.eu/android-networking-in-2019-retrofit-with-kotlins-coroutines-aefe82c4d777

I need to recover data in JSON format, I get the following error message :

com.squareup.moshi.JsonDataException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at path $*

I looked at this answer but I don't know how to adapt it to my code : Retrofit Expected BEGIN_OBJECT but was BEGIN_ARRAY

This is my interface

interface LocationService {
    @GET("locations?countryid=fr")
    fun getLocationList() : Deferred<Response<LocationResponse>>
}

LocationResponse

data class LocationResponse (val results : List<Location>)

Location Model

data class Location (
    @field:Json(name = "id") val id : String,
    @field:Json(name = "category") val category : String,
    @field:Json(name = "label") val label : String,
    @field:Json(name = "value") val value : String
)

The JSON is like this

[
  {
    "id":"city_39522",
    "category":"Villes",
    "label":"Parisot (81310)",
    "value":null
 },
 {
   "id":"city_36661",
   "category":"Villes",
   "label":"Paris 9ème (75009)",
   "value":null
 },
 {
   "id":"city_39743",
   "category":"Villes",
   "label":"Parisot (82160)",
   "value":null
 }
]

I'm already getting a list, I don't see how to correct the error ?

Answer 1

You have to update your interface as:

interface LocationService {
    @GET("locations?countryid=fr")
    fun getLocationList() : Deferred<Response<List<Location>>>
}

Also you don't need LocationResponse class and remove the below code:

data class LocationResponse (val results : List<Location>)

You are expecting the response and parsing it like this:

{
  "results": [
    { .. }
  ]
}

But Actual response is like this:

 [
    { .. }
  ]

The error explains that you are expecting object at the root but actual json data is array, so you have to change it to array.

Answer 2

In your API interface you're defining getLocationList() method to return a LocationResponse object whereas the API actually returns a list of objects, so to fix this define the method as follows..

interface LocationService {
    @GET("locations?countryid=fr")
    fun getLocationList() : Deferred<Response<List<Location>>>
}