Render a view to a Bitmap of a specific size

FirstFragment.kt

package `in`.obvious.android.bitmaptest

import android.graphics.Bitmap
import android.graphics.Canvas
import android.graphics.Matrix
import android.graphics.RectF
import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.Toast
import androidx.fragment.app.Fragment
import androidx.navigation.fragment.findNavController
import kotlinx.android.synthetic.main.fragment_first.*
import java.io.File

/**
 * A simple [Fragment] subclass as the default destination in the navigation.
 */
class FirstFragment : Fragment() {

    private val handler = Handler(Looper.getMainLooper())

    override fun onCreateView(
      inflater: LayoutInflater, container: ViewGroup?,
      savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_first, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        view.findViewById<Button>(R.id.button_first).setOnClickListener {
            val image = Bitmap.createBitmap(595, 842, Bitmap.Config.ARGB_8888)
            val sourceRect =
                RectF(0F, 0F, textview_first.width.toFloat(), textview_first.height.toFloat())
            val destRect = RectF(0F, 0F, image.width.toFloat(), image.height.toFloat())
            val matrix = Matrix()
            matrix.setRectToRect(sourceRect, destRect, Matrix.ScaleToFit.FILL)

            val canvas = Canvas(image)
            canvas.concat(matrix)
            textview_first.draw(canvas)

            Thread {
                val context = requireContext()

                val imageFile = File(context.filesDir, "image.png")
                imageFile
                    .outputStream()
                    .use { stream ->
                        image.compress(Bitmap.CompressFormat.PNG, 90, stream)
                        stream.flush()

                        handler.post {
                            Toast.makeText(context, "Image Saved!", Toast.LENGTH_SHORT).show()
                        }
                    }


            }.start()

        }
    }
}

fragment_first.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="#546E7A"
    tools:context=".FirstFragment">

    <TextView
        android:id="@+id/textview_first"
        android:layout_width="250dp"
        android:layout_height="354dp"
        android:text="@string/hello_first_fragment"
        app:layout_constraintBottom_toTopOf="@id/button_first"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:gravity="center"
        android:background="#E0E0E0"/>

    <Button
        android:id="@+id/button_first"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/next"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/textview_first" />
</androidx.constraintlayout.widget.ConstraintLayout>