QR Code Generate... create image... send as attachment...

Question

I have an existing Xamarin Forms App for Android only. A report function uses the Xamarin Community Toolkit "email" feature. The body of the email is a culmination of data. An end user request was to add a QR code with a piece of that data. I have installed ZXing component and am generating the onscreen barcode... all of this works fine. I need some assistance on how to add the qr code to the email as an attachment.

Can anyone provide some help in this area. I have attempted several approaches, but ZXing.Net.Mobile doesn't have a very straightforward way to do this... or the documentation is unclear.

Answer 1

Hello,

but I am having difficulty converting that to an image file for saving as a .bmp, .jpg to attach. The problem seems to be that most of the components that use .NET are using a different System.Drawing namespace and these throw errors in Xamarin Forms.

You cannot convert ImageSource to an image file, however, here is a workaround, you can show this Image control fullscreen, then you can take a screenshot. Then save this image to app folder like following code. I use a button click event for testing.

string targetFile;
private async void Button_Clicked(object sender, EventArgs e)
{
    var screenshot = await Screenshot.CaptureAsync();
    Stream stream = await screenshot.OpenReadAsync();

   // Create an output filename
    targetFile = Path.Combine(FileSystem.AppDataDirectory, "QRcode.jpg");
    // Copy the file to the AppDataDirectory
     FileStream outputStream = File.Create(targetFile);
    await stream.CopyToAsync(outputStream);
    stream.Close();
    outputStream.Close();   
}

Next, you can send email by this QRCode image.

private async void Button_Clicked_1(object sender, EventArgs e)
{
    
         var message = new EmailMessage
         {
             Subject = "Hello",
             Body = "World",
         };
         message.Attachments.Add(new EmailAttachment(targetFile));
         await Email.ComposeAsync(message);
}

Best Regards,

Leon Lu

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Answer 2

After many days of testing I have discovered one path that worked for me. I did not attempt every itteration but I was glad to be able to move on from this issue.

QRCoder has a number of "renderers". Some work on the Android platform, others do not. This is the code that finally worked for me.

For onscreen QRCode Images this worked in Xamarin Forms:

QRCodeGenerator qrGenerator = new QRCodeGenerator();
QRCodeData qrCodeData = qrGenerator.CreateQrCode(QRCodeString, QRCodeGenerator.ECCLevel.Q);
PngByteQRCode qrCode = new PngByteQRCode(qrCodeData);
QRCodeByteArray = qrCode.GetGraphic(QRPixels);
QRCodeImage.Source = ImageSource.FromStream(() => new MemoryStream(QRCodeByteArray));

The first two lines create the generator and are very standard across all. The third line of code creates a PNG byte array renderer. The array can be used in two ways. A byte array that can be streamed as a datasource, or a byte array that can be used to writer to a file on disk. I would have rather streamed the byte array directly in to an Email Message Attachment but using Xamarin Forms Community Toolkit the Email Message Attachment only allows using a file unlike a standard SMTP email attachment where it allows streaming an attachment.

To create the PNG file for attachment the code is virtually the same except I use the byte array and steam it to a file with the file name having a .png extension. line #4 above "QRCodeByteArray" is stored in my view model so I can refer to it when I require the attachment to be created. In this way I do not have to recreate the generator, or recreate the byte array. The byte array generated above is used in line two using statement. I then am ready to call the email compose.

var qrAttachmentFileName = Path.Combine(FileSystem.CacheDirectory, onDiskFileName);
using (var stream = new MemoryStream(QRCodeByteArray))
using (var newStream = File.OpenWrite(qrAttachmentFileName))
    await stream.CopyToAsync(newStream);