android kotlin - Coroutines download image from url

MainActivity.kt


package com.example.coroutine

import android.content.Context
import android.content.ContextWrapper
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.net.Uri
import android.os.Bundle
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import java.io.File
import java.io.FileOutputStream
import java.io.IOException
import java.io.OutputStream
import java.net.URL
import java.util.*


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

        val context = this

        // url of image to download
        val urlImage:URL = URL("https://images.pexels.com/photos/730344/" +
                "pexels-photo-730344.jpeg?" +
                "auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260")

        // show image url in text view
        tvDownload.text = urlImage.toString()


        button.setOnClickListener {
            it.isEnabled = false // disable button
            progressBar.visibility = View.VISIBLE

            // async task to get / download bitmap from url
            val result: Deferred<Bitmap?> = GlobalScope.async {
                urlImage.toBitmap()
            }

            GlobalScope.launch(Dispatchers.Main) {
                // get the downloaded bitmap
                val bitmap : Bitmap? = result.await()

                // if downloaded then saved it to internal storage
                bitmap?.apply {
                    // get saved bitmap internal storage uri
                    val savedUri : Uri? = saveToInternalStorage(context)

                    // display saved bitmap to image view from internal storage
                    imageView.setImageURI(savedUri)

                    // show bitmap saved uri in text view
                    tvSaved.text = savedUri.toString()
                }

                it.isEnabled = true // enable button
                progressBar.visibility = View.INVISIBLE
            }
        }
    }
}


// extension function to get / download bitmap from url
fun URL.toBitmap(): Bitmap?{
    return try {
        BitmapFactory.decodeStream(openStream())
    }catch (e:IOException){
        null
    }
}


// extension function to save an image to internal storage
fun Bitmap.saveToInternalStorage(context : Context):Uri?{
    // get the context wrapper instance
    val wrapper = ContextWrapper(context)

    // initializing a new file
    // bellow line return a directory in internal storage
    var file = wrapper.getDir("images", Context.MODE_PRIVATE)

    // create a file to save the image
    file = File(file, "${UUID.randomUUID()}.jpg")

    return try {
        // get the file output stream
        val stream: OutputStream = FileOutputStream(file)

        // compress bitmap
        compress(Bitmap.CompressFormat.JPEG, 100, stream)

        // flush the stream
        stream.flush()

        // close stream
        stream.close()

        // return the saved image uri
        Uri.parse(file.absolutePath)
    } catch (e: IOException){ // catch the exception
        e.printStackTrace()
        null
    }
}

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="#EDEAE0"
    tools:context=".MainActivity">

    <com.google.android.material.button.MaterialButton
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:backgroundTint="#7BB661"
        android:text="Download Image"
        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="16dp"
        android:visibility="invisible"
        app:layout_constraintBottom_toBottomOf="@+id/button"
        app:layout_constraintStart_toEndOf="@+id/button"
        app:layout_constraintTop_toTopOf="@+id/button" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="350dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tvDownload"
        tools:srcCompat="@tools:sample/avatars" />

    <TextView
        android:id="@+id/tvDownload"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        tools:text="Download URL"
        style="@style/TextAppearance.MaterialComponents.Subtitle2"
        android:padding="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />

    <com.google.android.material.textview.MaterialTextView
        android:id="@+id/tvSaved"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        tools:text="Saved Uri"
        android:padding="8dp"
        style="@style/TextAppearance.MaterialComponents.Subtitle1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />

</androidx.constraintlayout.widget.ConstraintLayout>

build.gradle (app) [dependencies]


// kotlin coroutine
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.7'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.7'