android kotlin - Volley example

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import android.util.Log
import android.widget.*
import com.android.volley.Request
import com.android.volley.toolbox.JsonObjectRequest
import org.json.JSONException


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 textView = findViewById<TextView>(R.id.textView)

        // Make text view text scrollable
        textView.movementMethod = ScrollingMovementMethod()

        // Data URL
        val url = "https://pastebin.com/raw/2bW31yqa"


        // Run volley
        button.setOnClickListener {
            // disable the button itself
            it.isEnabled = false

            textView.text = ""

            val jsonObjectRequest = JsonObjectRequest(
                Request.Method.GET, url, null,
                { response ->
                    // Process the JSON
                    try {
                        // Get the JSON array
                        val array = response.getJSONArray("students")

                        // Loop through the array elements
                        for (i in 0 until array.length()) {
                            // Get current json object
                            val student = array.getJSONObject(i)

                            // Get the current student (json object) data
                            val firstName = student.getString("firstname")
                            val lastName = student.getString("lastname")
                            val age = student.getString("age")

                            // Display the formatted json data in text view
                            textView.append("$firstName $lastName\nage : $age")
                            textView.append("\n\n")
                        }
                    } catch (e: JSONException) {
                        e.printStackTrace()
                    }
                }, { error ->
                    Log.d("error", error.toString())
                }
            )

            // Access the RequestQueue through singleton class.
            VolleySingleton.getInstance(this)
                .addToRequestQueue(jsonObjectRequest)
        }
    }
}
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" />

    <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'
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