Android - Extract Data From JSON Array using Retrofit Library with Jetpack Compose

package com.example.newcanaryproject.ui.theme

import androidx.compose.ui.graphics.Color

val Purple200 = Color(0xFF0F9D58)
val Purple500 = Color(0xFF0F9D58)
val Purple700 = Color(0xFF3700B3)
val Teal200 = Color(0xFF03DAC5)

// on below line we are adding different colors.
val greenColor = Color(0xFF0F9D58)

package com.example.newcanaryproject

// on below line we are creating a 
// modal class for our data class.
data class ListModal(
    // on below line we are creating two variable 
    // one is for language name which is string.
    val languageName: String
)

package com.example.newcanaryproject

import retrofit2.Call
import retrofit2.http.GET

interface RetrofitAPI {
    // as we are making get request so we are displaying
    // GET as annotation.
    // and inside we are passing last parameter for our url.
    @GET("T7R2")
    fun
    // as we are calling data from array so we are calling
    // it with array list and naming that method as getAllCourses();
            getLanguages(): Call<ArrayList<ListModal>>

}

package com.example.newcanaryproject

import android.content.Context
import android.os.Bundle
import android.widget.Toast
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.*
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.text.style.TextAlign
import androidx.compose.ui.unit.*
import com.example.newcanaryproject.ui.theme.*
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            NewCanaryProjectTheme {
                // on below line we are specifying background color for our application
                Surface(
                    // on below line we are specifying modifier and color for our app
                    modifier = Modifier.fillMaxSize(), color = MaterialTheme.colors.background
                ) {
                    // on the below line we are specifying the theme as scaffold.
                    Scaffold(

                        // in scaffold we are specifying top bar.
                        topBar = {

                            // inside top bar we are specifying background color.
                            TopAppBar(backgroundColor = greenColor,

                                // along with that we are specifying title for our top bar.
                                title = {

                                    // in the top bar we are specifying tile as a text
                                    Text(

                                        // on below line we are specifying 
                                        // text to display in top app bar.
                                        text = "JSON Parsing in Android",

                                        // on below line we are specifying 
                                        // modifier to fill max width.
                                        modifier = Modifier.fillMaxWidth(),

                                        // on below line we are
                                        // specifying text alignment.
                                        textAlign = TextAlign.Center,

                                        // on below line we are 
                                        // specifying color for our text.
                                        color = Color.White
                                    )
                                })
                        }) {
                        // on below line we are display list view
                          // method to display our list view.
                        displayListView()
                    }
                }
            }
        }
    }
}

fun getJSONData(courseList: MutableList<String>, ctx: Context) {
    // on below line we are creating a retrofit
    // builder and passing our base url
    val retrofit = Retrofit.Builder()
        .baseUrl("https://jsonkeeper.com/b/") 
        // on below line we are calling add
        // Converter factory as Gson converter factory.
        .addConverterFactory(GsonConverterFactory.create()) 
        // at last we are building our retrofit builder.
        .build()

    // below line is to create an instance for our retrofit api class.
    val retrofitAPI = retrofit.create(RetrofitAPI::class.java)

    // on below line we are calling a method to get all the courses from API.
    val call: Call<ArrayList<ListModal>> = retrofitAPI.getLanguages()

    // on below line we are calling method to enqueue and calling
    // all the data from array list.
    call!!.enqueue(object : Callback<ArrayList<ListModal>?> {
        override fun onResponse(
            call: Call<ArrayList<ListModal>?>,
            response: Response<ArrayList<ListModal>?>
        ) {
            // on below line we are checking if response is successful.
            if (response.isSuccessful) {
                // on below line we are creating a new list
                var lst: ArrayList<ListModal> = ArrayList()

                // on below line we are passing
                // our response to our list
                lst = response.body()!!

                // on below line we are passing 
                // data from lst to course list.
                for (i in 0 until lst.size) {
                    // on below line we are adding data to course list.
                    courseList.add(lst.get(i).languageName)
                }
            }
        }

        override fun onFailure(call: Call<ArrayList<ListModal>?>, t: Throwable) {
            // displaying an error message in toast
            Toast.makeText(ctx, "Fail to get the data..", Toast.LENGTH_SHORT)
                .show()
        }
    })
}

@Composable
fun displayListView() {
    val context = LocalContext.current
    // on below line we are creating and
    // initializing our array list
    val courseList = remember { mutableStateListOf<String>() }
    getJSONData(courseList, context)

    // on the below line we are creating a
    // lazy column for displaying a list view.
    // on below line we are calling lazy column
    // for displaying listview.
    LazyColumn {
        // on below line we are populating
        // items for listview.
        items(courseList) { language ->
            // on below line we are specifying ui for each item of list view.
            // we are specifying a simple text for each item of our list view.
            Text(language, modifier = Modifier.padding(15.dp))
            // on below line we are specifying
            // divider for each list item
            Divider()
        }
    }
}