A QR code is a computer-readable identification that contains data about the item to which it is attached. The article demonstrates how to return the QR Code image as a response from .Net Core API.

• Visual Studio or Visual Studio Code already installed

• Install the below package, i.e., “QRCoder” via NuGet package manager.

  Install-Package QRCoder

The “QRCoder” DLL helps to generate QR code with just four lines of code in C#.

QRCodeGenerator qrGenerator = new QRCodeGenerator();
QRCodeData qrCodeData = qrGenerator.CreateQrCode(qrText, QRCodeGenerator.ECCLevel.Q);
QRCode qrCode = new QRCode(qrCodeData);
Bitmap qrCodeImage = qrCode.GetGraphic(20);

Create an instance of the QRCodeGenerator class.

QRCodeGenerator qrGenerator = new QRCodeGenerator();

The next step is to initialize QR code data using the CreateQrCode method, which takes two arguments, i.e., string text for encoding inside the QR code, and another case defines the error correction level, i.e., ECCLevel.

Here, four different levels L (7%), M (15%), Q (25%) and H (30%) are available, whereby the percentage represents the hidden portion of the QR-code until the error correction algorithm can’t recreate the original message encoded in the QR code.

QRCodeData qrCodeData = qrGenerator.CreateQrCode(qrText, QRCodeGenerator.ECCLevel.Q);

The next step is to create the QR-code using the data initialized above.

QRCode qrCode = new QRCode(qrCodeData);

Finally, represent the QR code into a graphical image, as shown below. The GetGraphic method takes one argument, which defines the size of QR-code. The GetGraphic method return image in the form of Bitmap by default.

Bitmap qrCodeImage = qrCode.GetGraphic(20);

Controller GET route snippet uses the QR-code library and returns the QR code image as a response.

[HttpGet]
[Route("qenerate/{qrText}")]
public IActionResult GetQrCode(string qrText)
{
	QRCodeGenerator qrGenerator = new QRCodeGenerator();
	QRCodeData qrCodeData = qrGenerator.CreateQrCode(qrText, QRCodeGenerator.ECCLevel.Q);
	QRCode qrCode = new QRCode(qrCodeData);
	Bitmap qrCodeImage = qrCode.GetGraphic(20);
	return File(BitmapToBytes(qrCodeImage), "image/jpeg");
}

QR-code, by default, generates a Bitmap, below function used to convert Bitmap to bytes.

private static Byte[] BitmapToBytes(Bitmap img)
{
	using (MemoryStream stream = new MemoryStream())
	{
		img.Save(stream, System.Drawing.Imaging.ImageFormat.Png);
		return stream.ToArray();
	}
}

**//Set color by using Color-class types**
Bitmap qrCodeImage = qrCode.GetGraphic(20, Color.DarkRed, Color.PaleGreen, true);
**//Set color by using HTML hex color notation**
Bitmap qrCodeImage = qrCode.GetGraphic(20, "#000ff0", "#0ff000");
**//Set logo in center of QR-code**
Bitmap qrCodeImage = qrCode.GetGraphic(20, Color.Black, Color.White, (Bitmap)Bitmap.FromFile("C:\\myimage.png"));

Github Repo

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