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.

Setup

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

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Install-Package QRCoder

Implementation

Define an Interface and Implementation

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

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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.

API Controller Integration

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

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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");
    }
}

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).

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

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.

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