【Kotlin/Android】ZXingでQRコードを生成とリーダーを実装する方法！

dependencies {
    // ZXing(QRコード生成&読み取り)
    implementation 'com.journeyapps:zxing-android-embedded:4.3.0'
}

AndroidManifest.xml
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
+   <uses-permission android:name="android.permission.CAMERA" />
    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"

activity_qr_reader.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.journeyapps.barcodescanner.DecoratedBarcodeView
        android:id="@+id/barcode_scanner"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

QRReaderActivity.kt
class QRReaderActivity : ComponentActivity() {
    
    private lateinit var barcodeView: DecoratedBarcodeView

    @SuppressLint("MissingInflatedId")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_second)

        barcodeView = findViewById(R.id.barcode_scanner)
        barcodeView.decodeContinuous(callback)

        // カメラの権限リクエスト
        if (ContextCompat.checkSelfPermission(this, android.Manifest.permission.CAMERA)
            != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, arrayOf(android.Manifest.permission.CAMERA), 1)
        }
    }

    private val callback = object : BarcodeCallback {
        // QRコードを読み取り完了した場合
        override fun barcodeResult(result: BarcodeResult?) {
            result?.let {
                barcodeView.pause()
                val qrCode = it.text
                Log.d("QR Code ", "${qrCode}")
            }
        }

        override fun possibleResultPoints(resultPoints: List<com.google.zxing.ResultPoint>) {
        }
    }

    override fun onResume() {
        super.onResume()
        barcodeView.resume()
    }

    override fun onPause() {
        super.onPause()
        barcodeView.pause()
    }

    // 権限リクエストの結果を処理するメソッド
    override fun onRequestPermissionsResult(
        requestCode: Int,
        permissions: Array<out String>,
        grantResults: IntArray
    ) {
        if (requestCode == 1) {
            if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                barcodeView.resume()
            } else {
                Log.d("Permission", "カメラの権限が拒否されました。")
            }
        }
        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
    }
}

readButton.setOnClickListener{
    val intent = Intent(this, QRReaderActivity::class.java)
    startActivity(intent)
}

fun generateQRCode(text: String, width: Int, height: Int): Bitmap? {
    val qrCodeWriter = QRCodeWriter()
    return try {
        val bitMatrix: BitMatrix = qrCodeWriter.encode(text, BarcodeFormat.QR_CODE, width, height)
        val bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565)
        for (x in 0 until width) {
            for (y in 0 until height) {
                bitmap.setPixel(x, y, if (bitMatrix[x, y]) android.graphics.Color.BLACK else android.graphics.Color.WHITE)
            }
        }
        bitmap
    } catch (e: WriterException) {
        e.printStackTrace()
        null
    }
}

qrCordViewButton.setOnClickListener{
    val qrCodeBitmap = generateQRCode("https://appdev-room.com/", 500, 500)
    findViewById <ImageView>(R.id.qr_code_view).setImageBitmap(qrCodeBitmap)
}