Simple QRView for Android using ZXING

QrView.kt

import android.content.Context
import android.graphics.*
import android.os.Build
import android.view.View
import com.google.zxing.BarcodeFormat
import com.google.zxing.EncodeHintType
import com.google.zxing.qrcode.QRCodeWriter
import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel
import java.util.*

class QrView(ctx: Context): View(ctx) {

    private val paint = Paint().apply {
        isDither = false
        isAntiAlias = false
        color = Color.BLACK
    }

    private var bitmap: Bitmap? = null
    private val srcRect = Rect()
    private val dstRect = Rect()

    var text: String? = null
        set(value) {
            if (field == value)
                return
            field = value
            bitmap?.recycle()
            bitmap = null
            invalidate()
        }

    var color: Int = Color.BLACK
        set(value) {
            field = value
            paint.color = value // For ALHA_8
            paint.colorFilter = PorterDuffColorFilter(value, PorterDuff.Mode.SRC_ATOP) // For ARGB_8888
            invalidate()
        }

    override fun onDraw(canvas: Canvas) {
        val text = text ?: return
        if (text.isEmpty()) return
        val bitmap = bitmap ?: generateQr(text)
        srcRect.right = bitmap.width
        srcRect.bottom = bitmap.height
        val sz = Math.min(canvas.width, canvas.height)
        dstRect.right = sz
        dstRect.bottom = sz
        canvas.drawBitmap(bitmap, srcRect, dstRect, paint)
    }

    companion object {

        private fun generateQr(text: String): Bitmap {
            val hintMap = Hashtable<EncodeHintType, ErrorCorrectionLevel>()
            hintMap[EncodeHintType.ERROR_CORRECTION] = ErrorCorrectionLevel.H
            val qrw = QRCodeWriter()
            val bitMatrix = qrw.encode(text, BarcodeFormat.QR_CODE, 0, 0)
            val size = bitMatrix.width
            val pixels = IntArray(size * size) {
                if (bitMatrix[it / size, it % size])
                    Color.BLACK
                else
                    Color.TRANSPARENT
            }
            // ALPHA_8 doesn't worked for me on 5.1, but worked on 8.0 and 8.1
            // I dunno why, so here we go
            return Bitmap.createBitmap(pixels, size, size,
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O)
                    Bitmap.Config.ALPHA_8
                else
                    Bitmap.Config.ARGB_8888
            )
        }

    }

}