Ytukyg

I am trying to convert a JSON string into a JSON data class object. The compiler does not complain, the Android Studio 3 IDE provides the necessary hints to correct code. Still I get a runtime error saying that JSONObject cannot be cast. Please any hints...

I have the following code:

fun startReplay() {

    doAsync {

        triggerServerFile(eventDomain + "/get-replay-JSON.php")

        val jsonString = getServerFile(eventDomain + "/data/replay-SidR2018.json?nocache=" + Math.random())

        uiThread {

            var replayData:replayDataObject = JSONObject(jsonString) as replayDataObject

            val a= replayData.component1()

            val b= replayData.component2()[3].component3()

        }

    }

}

and the following data classes:

data class replayDataObject(

    val event: String,

    val shiptracks: List<Shiptrack>,

    val windtracks: List<Windtrack>

)



data class Shiptrack(

    val colorcode: String,

    val course: List<String>,

    val lat: List<String>,

    val lon: List<String>,

    val name: String,

    val speed: List<String>,

    val stamp: List<String>

)



data class Windtrack(

    val course: List<String>,

    val lat: List<String>,

    val lon: List<String>,

    val name: String,

    val speed: List<String>,

    val stamp: List<String>

)

and finally the following JSON string:

{

    "event": "SidR2018,Slag in de Rondte 2018",

    "shiptracks": [{

            "name": "Hollandia",

            "colorcode": "0",

            "stamp": ["1541407570", "1541407599"],

            "lat": ["53.173461666667", "53.17347"],

            "lon": ["5.409655", "5.409655"],

            "speed": ["0", "0"],

            "course": ["299", "301"]

        }, {

            "name": "Ouderzorg",

            "colorcode": "14",

            "stamp": ["1541407540", "1541407540", "1541407540"],

            "lat": ["53.17359", "53.17359", "53.17359"],

            "lon": ["5.409586", "5.409586", "5.409586"],

            "speed": ["0", "0", "0"],

            "course": ["0", "0", "0"]

        }

    ],

    "windtracks": [{

            "name": "Arcen",

            "stamp": ["1541409000", "1541411400"],

            "lat": ["51.5", "51.5"],

            "lon": ["6.2", "6.2"],

            "speed": ["4", "2"],

            "course": ["72", "61"]

        }, {

            "name": "Zeeplatform K13",

            "stamp": ["1541408400", "1541410800", "1541412000", "1541414400"],

            "lat": ["53.22", "53.22", "53.22", "53.22"],

            "lon": ["3.22", "3.22", "3.22", "3.22"],

            "speed": ["16", "16", "17", "16"],

            "course": ["126", "129", "127", "120"]

        }

    ]

}

The stack trace (line 381 is the line in the code containing JSOBObject:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: nl.zeilvaartwarmond.ttandroid.szwtracktrace, PID: 23370
java.lang.ClassCastException: org.json.JSONObject cannot be cast to nl.zeilvaartwarmond.ttandroid.szwtracktrace.MapsActivity$replayDataObject
at nl.zeilvaartwarmond.ttandroid.szwtracktrace.MapsActivity$startReplay$1$1.invoke(MapsActivity.kt:381)
at nl.zeilvaartwarmond.ttandroid.szwtracktrace.MapsActivity$startReplay$1$1.invoke(MapsActivity.kt:44)
at org.jetbrains.anko.AsyncKt$uiThread$1.run(Async.kt:70)
at android.os.Handler.handleCallback(Handler.java:898)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:198)
at android.app.ActivityThread.main(ActivityThread.java:6716)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

You need something that interprets the JSON to map it to the replayDataObject. In Kotlin, data classes are very good at this using any of a number of libraries.

Google Gson

https://github.com/google/gson

After initializing Gson, you would simply take that String:

gson.fromJson(jsonString, replayDataObject::class.java)

Now, a word of warning, you have a lot of non-nullable types in there, and there may be issues with the data you read in, or what you expect from it.

Other libraries:

• https://github.com/cbeust/klaxon


• https://github.com/square/moshi

Retrofit work for you.
Get json from server and convert to object.

https://square.github.io/retrofit/