Android - Extract Data From JSON Array using Retrofit Library with Kotlin

package com.gtappdevelopers.kotlingfgproject

data class CourseRVModal(
    // on below line we are creating 
    // two variable one for 
    // course name and other for course image.
    var languageName: String,
    var languageImg: String
)

package com.gtappdevelopers.kotlingfgproject

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.squareup.picasso.Picasso

// on below line we are creating
// a course rv adapter class.
class CourseRVAdapter(
    // on below line we are passing variables 
    // as course list and context
    private var courseList: ArrayList<CourseRVModal>,
) : RecyclerView.Adapter<CourseRVAdapter.CourseViewHolder>() {
    override fun onCreateViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): CourseRVAdapter.CourseViewHolder {
        // this method is use to inflate the layout file which 
        // we have created for our recycler view.
        // on below line we are inflating our layout file.
        val itemView = LayoutInflater.from(parent.context).inflate(
            R.layout.course_rv_item,
            parent, false
        )
        // at last we are returning our view 
        // holder class with our item View File.
        return CourseViewHolder(itemView)
    }

    override fun onBindViewHolder(holder: CourseRVAdapter.CourseViewHolder, position: Int) {
        // on below line we are setting data to our text view and our image view.
        holder.courseNameTV.text = courseList.get(position).languageName
        Picasso.get().load(courseList.get(position).languageImg).into(holder.courseIV)
    }

    override fun getItemCount(): Int {
        // on below line we are 
        // returning our size of our list
        return courseList.size
    }

    class CourseViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // on below line we are initializing our 
        // course name text view and our image view.
        val courseNameTV: TextView = itemView.findViewById(R.id.idTVCourse)
        val courseIV: ImageView = itemView.findViewById(R.id.idIVCourse)
    }
}

package com.gtappdevelopers.kotlingfgproject

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("0RH6")
    fun getAllCourses(): Call<ArrayList<CourseRVModal>?>?
}

package com.gtappdevelopers.kotlingfgproject

import android.os.Bundle
import android.view.View
import android.widget.ProgressBar
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.RecyclerView
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

class MainActivity : AppCompatActivity() {

    // on below line we are creating variables.
    lateinit var courseRV: RecyclerView
    lateinit var loadingPB: ProgressBar
    lateinit var courseRVAdapter: CourseRVAdapter
    lateinit var courseList: ArrayList<CourseRVModal>

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        // on below line we are initializing 
        // our variable with their ids.
        courseRV = findViewById(R.id.idRVCourses)
        loadingPB = findViewById(R.id.idPBLoading)

        // on below line we are initializing our list
        courseList = ArrayList()

        // on below line we are calling 
        // get all courses method to get data.
        getAllCourses()

    }

    private fun getAllCourses() {
        // 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.
             // at last we are building our retrofit builder.
            .addConverterFactory(GsonConverterFactory.create()) 
            .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<CourseRVModal>?>? = retrofitAPI.getAllCourses()

        // on below line we are calling method to enqueue and calling
        // all the data from array list.
        call!!.enqueue(object : Callback<ArrayList<CourseRVModal>?> {
            override fun onResponse(
                call: Call<ArrayList<CourseRVModal>?>,
                response: Response<ArrayList<CourseRVModal>?>
            ) {
                if (response.isSuccessful) {
                    loadingPB.visibility = View.GONE
                    courseList = response.body()!!
                }

                // on below line we are initializing our adapter.
                courseRVAdapter = CourseRVAdapter(courseList)

                // on below line we are setting adapter to recycler view.
                courseRV.adapter = courseRVAdapter

            }

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