android kotlin - ImageView rounded corners transparent

MainActivity.kt


package com.example.jetpack

import android.content.Context
import android.graphics.*
import android.os.Bundle
import android.util.TypedValue
import androidx.appcompat.app.AppCompatActivity
import androidx.core.graphics.drawable.RoundedBitmapDrawable
import androidx.core.graphics.drawable.RoundedBitmapDrawableFactory
import kotlinx.android.synthetic.main.activity_main.*
import java.io.IOException


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

        // get bitmap from assets folder
        val bitmap: Bitmap? = assetsToBitmap("flower8.jpg")

        // show the bitmap on first image view
        bitmap?.apply { imageView.setImageBitmap(this) }

        // convert the bitmap to rounded corners bitmap drawable
        bitmap?.apply {
            val drawable = roundedCorners(
                context = applicationContext,
                radius = 50.dpToPixels(applicationContext)
            )
            // show the transparent rounded corners bitmap drawable
            imageView2.setImageDrawable(drawable)
        }
    }
}


// extension function to get rounded corners bitmap drawable from bitmap
fun Bitmap.roundedCorners(
    context: Context,
    radius: Float = 25F
):RoundedBitmapDrawable{
    return RoundedBitmapDrawableFactory.create(
     context.resources, this
    ).apply {
        setAntiAlias(true)
        // sets the corner radius to be applied when drawing the bitmap
        cornerRadius = radius
    }
}


// extension function to convert dp to equivalent pixels
fun Int.dpToPixels(context: Context):Float = TypedValue.applyDimension(
    TypedValue.COMPLEX_UNIT_DIP, this.toFloat(), context.resources.displayMetrics
)


// extension function to get bitmap from assets
fun Context.assetsToBitmap(fileName: String): Bitmap?{
    return try {
        with(assets.open(fileName)){
            BitmapFactory.decodeStream(this)
        }
    } catch (e: IOException) { 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:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#DCDCDC"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="280dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="0dp"
        android:layout_height="280dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView"
        tools:srcCompat="@tools:sample/avatars" />

</androidx.constraintlayout.widget.ConstraintLayout>