QR Code Generator Function in Kotlin

QR codes have become a ubiquitous tool for encoding information, from website links to product information. As a developer, being able to generate QR codes programmatically can be a useful skill. In this guide, we’ll take a look at how to write a QR code generator function in Kotlin.

Step 1: Add the Dependency

First, we need to add the necessary dependency to our project. We’ll be using the ZXing library, which provides a simple API for creating QR codes. To add the library to our Gradle project, we can add the following line to our build.gradle file:

implementation 'com.google.zxing:core:3.4.1'

Step 2: Generate the QR Code

With the dependency added, we can now write our QR code generator function. The following code will generate a QR code from a String and return it as a Bitmap:

import com.google.zxing.EncodeHintType
import com.google.zxing.qrcode.QRCodeWriter
import com.google.zxing.BarcodeFormat
import com.google.zxing.client.j2se.MatrixToImageWriter
import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel
import java.util.HashMap
import android.graphics.Bitmap
import android.graphics.Color

fun generateQRCode(text: String, size: Int = 400): Bitmap {
    val hints = HashMap<EncodeHintType, Any>()
    hints[EncodeHintType.CHARACTER_SET] = "UTF-8"
    hints[EncodeHintType.ERROR_CORRECTION] = ErrorCorrectionLevel.H

    val writer = QRCodeWriter()
    val bitMatrix = writer.encode(text, BarcodeFormat.QR_CODE, size, size, hints)
    val bitmap = MatrixToImageWriter.toBitmap(bitMatrix)

    // Add coloring
    for (i in 0 until bitmap.width) {
        for (j in 0 until bitmap.height) {
            if (bitMatrix.get(i, j)) {
                bitmap.setPixel(i, j, Color.BLACK)
            } else {
                bitmap.setPixel(i, j, Color.WHITE)
            }
        }
    }

    return bitmap
}

Let’s break down how the function works:

1. We create a HashMap of hints to configure the QR code generator. In this example, we set the character set to "UTF-8" and the error correction level to "H".

2. We create a QRCodeWriter instance and use it to encode the input text as a QR code. The encoding process returns a BitMatrix, which is a representation of the QR code as a binary matrix.

3. We use the MatrixToImageWriter class to convert the BitMatrix to a BufferedImage, which we can then use as the basis for our Bitmap.

4. We loop through the Bitmap and set the pixel colors based on the corresponding value in the BitMatrix. If the value is true (representing a black pixel), we set the color to Color.BLACK. Otherwise, we set the color to Color.WHITE.

5. Finally, we return the generated Bitmap.

Step 3: Use the Generator

With our QR code generator function written, we can now use it to generate QR codes from our Kotlin code. Here’s an example of how to use the function:

val text = "Hello, world!"
val size = 500
val qrCode = generateQRCode(text, size)

This code will generate a QR code with the text "Hello, world!" and a size of 500 pixels. The resulting Bitmap will be stored in the qrCode variable.

Conclusion

In this guide, we’ve looked at how to write a QR code generator function in Kotlin using the ZXing library. With this function, you can easily generate QR codes from your Kotlin code for use in a variety of contexts.