android kotlin - Volley JsonArrayRequest

MainActivity.kt


package com.cfsuman.kotlintutorials

import android.app.Activity
import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import android.view.View
import android.widget.*
import com.android.volley.Request
import com.android.volley.toolbox.JsonArrayRequest
import org.json.JSONException
import org.json.JSONObject


class MainActivity : Activity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // get the widgets reference from XML layout
        val button = findViewById<Button>(R.id.button)
        val progressBar = findViewById<ProgressBar>(R.id.progressBar)
        val textView = findViewById<TextView>(R.id.textView)

        // make text view content scrollable
        textView.movementMethod = ScrollingMovementMethod()

        // url to get json array
        val url = "https://pastebin.com/raw/Em972E5s"


        // get json array from url using volley network library
        button.setOnClickListener {
            // disable the button itself
            it.isEnabled = false

            progressBar.visibility = View.VISIBLE

            // request json array response from the provided url
            val request = JsonArrayRequest(
                Request.Method.GET, // method
                url, // url
                null, // json request
                {response -> // response listener
                    try {
                        textView.text = ""

                        // loop through the array elements
                        for (i in 0 until  response.length()){
                            // get current json object as student instance
                            val student: JSONObject = response.getJSONObject(i)

                            // get the current student (json object) data
                            val firstName: String = student
                                .getString("firstname")
                            val lastName: String = student
                                .getString("lastname")
                            val age: Int = student.getInt("age")

                            // display the formatted json data in text view
                            textView.append("$firstName " +
                                    "$lastName\nAge : $age\n\n")
                        }

                    }catch (e: JSONException){
                        textView.text = e.message
                    }

                    progressBar.visibility = View.INVISIBLE
                },
                {error -> // error listener
                    textView.text = error.message
                    progressBar.visibility = View.INVISIBLE
                }
            )

            // add network request to volley queue
            VolleySingleton.getInstance(applicationContext)
                .addToRequestQueue(request)
        }
    }
}

VolleySingleton.kt


package com.cfsuman.kotlintutorials

import android.content.Context
import com.android.volley.Request
import com.android.volley.RequestQueue
import com.android.volley.toolbox.Volley

class VolleySingleton constructor(context: Context) {
    companion object {
        @Volatile
        private var INSTANCE: VolleySingleton? = null
        fun getInstance(context: Context) =
            INSTANCE ?: synchronized(this) {
                INSTANCE ?: VolleySingleton(context).also {
                    INSTANCE = it
                }
            }
    }
    private val requestQueue: RequestQueue by lazy {
        // applicationContext is key, it keeps you from leaking the
        // Activity or BroadcastReceiver if someone passes one in.
        Volley.newRequestQueue(context.applicationContext)
    }
    fun <T> addToRequestQueue(req: Request<T>) {
        requestQueue.add(req)
    }
}

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#DCDCDC"
    android:padding="24dp">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Run Volley"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:visibility="invisible"
        app:layout_constraintBottom_toBottomOf="@+id/button"
        app:layout_constraintStart_toEndOf="@+id/button"
        app:layout_constraintTop_toTopOf="@+id/button" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="16dp"
        android:fontFamily="sans-serif"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>

gradle dependencies


// Volley network library
implementation 'com.android.volley:volley:1.2.1'