There are multiple ways to generate QR codes. This article demonstrates how to use QRCoder—a lightweight and easy-to-use library that supports concurrent generation without relying on third-party dependencies.

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Setup

First, add the QRCoder package to your project via PowerShell:

Install-Package QRCoder

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Implementation

Define an Interface and Implementation

Create an IQRCode interface and its corresponding class to generate QR codes:

using QRCoder;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

public interface IQRCode
{
    byte[] GenerateQRCode(string content);
}

public class QRCode : IQRCode
{
    public byte[] GenerateQRCode(string content)
    {
        var generator = new QRCodeGenerator();
        var codeData = generator.CreateQrCode(content, QRCodeGenerator.ECCLevel.M, true);
        QRCoder.QRCode qrcode = new QRCoder.QRCode(codeData);

        // Generate bitmap image and convert to byte array
        var bitmapImg = qrcode.GetGraphic(
            pixelsPerModule: 10,
            darkColor: Color.Black,
            lightColor: Color.White,
            drawQuietZones: false
        );

        using MemoryStream stream = new MemoryStream();
        bitmapImg.Save(stream, ImageFormat.Jpeg);
        return stream.ToArray();
    }
}

Key Parameters of GetGraphic()

• pixelsPerModule: Pixel size per QR code module (larger values increase image resolution). • darkColor: Color of the QR code's dark modules (typically Color.Black). • lightColor: Color of the QR code's light modules (typically Color.White). • icon: Optional watermark image (e.g., a logo) to embed in the QR code center. • iconSizePercent: Size percentage of the watermark relative to the QR code. • iconBorderWidth: Border width around the watermark. • drawQuietZones: Whether to include empty margins around the QR code to improve readability.

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API Controller Integration

Inject the IQRCode service into an API controller to return the QR code as an image:

using Microsoft.AspNetCore.Mvc;

[Route("api/[controller]")]
[ApiController]
public class QrCodeController : ControllerBase
{
    [HttpGet]
    public FileContentResult QrCode(
        [FromServices] IQRCode _qrcode, 
        string content
    )
    {
        var buffer = _qrcode.GenerateQRCode(content);
        return File(buffer, "image/jpeg");
    }
}

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Usage

• Plain Text: If content is plain text (e.g., "Hello, World!"), scanning the QR code will display the text. • URL: If content is a valid URL (e.g., "https://example.com"), scanning will open the link directly.

Example Output When the API is called with a URL, the generated QR code image will enable quick redirection to the specified webpage. Below is a textual representation of the QR code's expected output format (image omitted for brevity).

[Sample QR Code Image: Contains black modules on white background encoding the provided content]

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Advantages

• Simplicity: Minimal code required to generate QR codes. • Customization: Adjust QR code colors, size, and embed logos. • Integration: Easily integrates with ASP.NET Core for API-driven applications.

By leveraging QRCoder, you can efficiently generate QR codes tailored to your application's needs.

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GitHub Repository: https://github.com/codebude/QRCoder