android kotlin - Volley post request with parameters

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import android.widget.*
import com.android.volley.DefaultRetryPolicy
import com.android.volley.Request
import com.android.volley.toolbox.JsonObjectRequest
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 textView = findViewById<TextView>(R.id.textView)

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


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

            val url = "https://postman-echo.com/post"
            textView.text = ""

            // Post parameters
            // Form fields and values
            val params = HashMap<String,String>()
            params["foo1"] = "bar1"
            params["foo2"] = "bar2"
            val jsonObject = JSONObject(params as Map<*, *>?)

            // Volley post request with parameters
            val request = JsonObjectRequest(
                Request.Method.POST,url,jsonObject,
                { response ->
                    // Process the json
                    try {
                        textView.text = "Response: $response"
                    } catch (e: Exception) {
                        textView.text = "Exception: $e"
                    }

                }, {
                    // Error in request
                    textView.text = "Volley error: $it"
                })


            // Volley request policy, only one time request to
            // avoid duplicate transaction
            request.retryPolicy = DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS,
                // 0 means no retry
                0, // DefaultRetryPolicy.DEFAULT_MAX_RETRIES = 2
                1f // DefaultRetryPolicy.DEFAULT_BACKOFF_MULT
            )

            // Add the volley post request to the request queue
            VolleySingleton.getInstance(this)
                .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" />

    <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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