get array from inside many objects in kotlin

Question

l am try to build simple app provide flight schedule . the problem is l have many object in json url and the array list inside of these object and l cant to get array list from objects because l got error fatal Caused by: org.json.JSONException: Value

my data json api

{
  "result": {
    "response": {
      "airport": {
        "pluginData": {
          "schedule": {
            "arrivals": {
              "data": [
                {
                  "flight": {
                    "identification": {
                      "id": null,
                      "row": 4832637003,
                      "number": {
                        "default": "ZP4801",
                        "alternative": null
                      },
                      "callsign": null,
                      "codeshare": null
                    }
                  }
                }
              ]
            }
          }
        }
      }
    }
  }
}

my code for getting data json of array list

  private fun handleJson (jsonString: String?){

        val jsonArray = JSONArray(jsonString)
        val list =  ArrayList<FlightShdu>()
        var x = 0
        while (x < jsonArray.length()){

            val jsonObject = jsonArray.getJSONObject(x)


            list.add(FlightShdu(

                jsonObject.getInt("id"),
                jsonObject.getString("callsign")

            ))


            x++
        }
        val adapter = ListAdapte(this@MainActivity,list)
        flightShdu_list.adapter = adapter

    }

val jsonArray = JSONArray(jsonString). JSON arrays start with [. Your JSON start with {. So it's an object, not an array. — JB Nizet
– JB Nizet, Commented Nov 4, 2018 at 14:07
@JBNizet the objects i want get from json is inside of data [1] you can take look in my link [jsoneditoronline.org/?id=38a83e0996cd4d1a823a55755907c629] — Ali Ghassan
– Ali Ghassan, Commented Nov 4, 2018 at 14:11
Your link is invalid. Post, in the question itself, the actual value of jsonString, and the exact and complete stack trace of the exception. — JB Nizet
– JB Nizet, Commented Nov 4, 2018 at 14:14
Parse your string as a JSONObject. You can then access the unique property, named "result", of that JSONObject. Since its' value, once again, starts with {, this is a JSONObject, too. So you can access its unique property named ""airport". Repeat until you reach the property named "data". Its value starts with a [, so it's an array this time, not an object. Its first element, at index 0, starts with a {, so it's once again an object. You should now get the idea. — JB Nizet
– JB Nizet, Commented Nov 4, 2018 at 14:27

Benjamin Charais · Accepted Answer · 2020-04-02 20:10:40Z

I would normally suggest for a full structure of the JSON via data classes, as this methodology could potentially be expensive to run multiple times over and over... The following highlights a method to dig into the JSON through jsonObjects by name, and then take the final layer of "identification" and populates a data class that is serializable with the resulting object

import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json
import kotlinx.serialization.json.JsonConfiguration
import kotlinx.serialization.json.JsonDecodingException
import kotlinx.serialization.json.JsonElement

val data =
"""
{
 "result": {
  "response": {
   "airport": {
    "pluginData": {
     "schedule": {
      "arrivals": {
       "data": [{
        "flight": {
         "identification": {
          "id": null,
          "row": 4832637003,
          "number": {
           "default": "ZP4801",
           "alternative": null
          },
         "callsign": null,
         "codeshare": null
         }
        }
       }]
      }
     }
    }
   }
  }
 }
}
"""

@Serializable
data class FlightIdentification(
    val id: Int?,
    val row: String,
    val number: IdentificationNumber,
    val callsign: String?,
    val codeshare: String?
) {
    @Serializable
    data class IdentificationNumber(
        val default: String,
        val alternative: String?
    )
}

val json = Json(JsonConfiguration.Stable)

fun JsonElement?.get(name: String): JsonElement? {
    return if (this == null) null
    else this.jsonObject[name]
}

fun handleJson(jsonString: String) {
    val obj = json.parseJson(jsonString)

    val data = obj.get("result").get("response").get("airport").get("pluginData")
        .get("schedule").get("arrivals").get("data")

    if (data != null) {
        val flight = data.jsonArray[0]
            .get("flight").get("identification")
        try {
            val res = json.parse(FlightIdentification.serializer(), flight.toString())

            println(res)
        } catch (e: JsonDecodingException) {
            println("Decode: ${e.message}")
        }
    }
}

handleJson(data)

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