android kotlin - Volley string request

Android Kotlin - Volley String Request: Breakdown

This code demonstrates using Volley, a popular Android network library, to fetch a string response from a URL using Kotlin. The code consists of three parts:

MainActivity.kt: This file defines the main activity of the app. It contains the user interface elements (button, progress bar, and text view) and handles user interaction with the button.
VolleySingleton.kt: This file implements a singleton class for managing the Volley request queue. This ensures there's only one instance of the request queue, improving efficiency.
activity_main.xml: This file defines the layout of the main activity screen, including the button, progress bar, and text view.

How it Works

UI Setup: When the activity starts (onCreate), the code retrieves references to the button, progress bar, and text view from the layout. It also enables scrolling for the text view to accommodate longer responses.
Fetch String on Button Click: Clicking the "Run Volley" button triggers the following actions:
- The button is disabled to prevent multiple clicks.
- The progress bar is shown to indicate ongoing network activity.
- A StringRequest object is created. This object defines the request type (GET in this case), URL to fetch, and two listener functions.
  - The first listener ({ response -> ... }) handles a successful response. It hides the progress bar and displays the fetched string in the text view.
  - The second listener ({error -> ... }) handles any errors during the request. It hides the progress bar and displays an error message in the text view.
- The StringRequest object is added to the request queue managed by the VolleySingleton class.
VolleySingleton: This class provides a single instance of the request queue, accessible throughout the application. It uses application context to avoid memory leaks and allows adding any type of Volley request (not just StringRequest) to the queue.

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.StringRequest


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 fetch string
        val url = "https://android--code.com/"


        // fetch string from url using volley network library
        button.setOnClickListener {
            // disable the button itself
            it.isEnabled = false

            progressBar.visibility = View.VISIBLE

            // request a string response from the provided url
            val stringRequest = StringRequest(
                Request.Method.GET, url,
                { response ->
                    progressBar.visibility = View.INVISIBLE

                    // display the response string on text view
                    textView.text = response
                },{error->
                    progressBar.visibility = View.INVISIBLE
                    textView.text = error.message
                }
            )

            VolleySingleton.getInstance(applicationContext)
                .addToRequestQueue(stringRequest)
        }
    }
}

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'