在Xamarin.Forms应用程序中使用ZXing.Net.Mobile进行二维码渲染

Question

I'm trying to use ZXing.Net.Mobile to display a QR code as an image.

I'm having difficulty getting the byte[] returned from BarcodeWriter.Writer(...) into an image for display.

ie this does not display an image

public class BarcodePage : ContentPage
{
    public BarcodePage()
    {
        Image image = new Image();

        image.Source = ImageSource.FromStream(() => 
        {
            var writer = new BarcodeWriter 
            {
                Format = BarcodeFormat.QR_CODE,
                Options = new EncodingOptions 
                {
                    Height = 200,
                    Width = 600
                }
            };

            var bitmapBytes = writer.Write ("Some text");
            return new MemoryStream(bitmapBytes);
        });

        Content = image;
    }
}

The bitmapBytes byte array looks like it has reasonable values in the debugger, how can I turn that into an image for display?

If I change the Image.Source assignment to:

image.Source = ImageSource.FromUri(new Uri("http://i.imgur.com/q0aIYvC.png"));

then it does correctly display the image, so I know the problem isn't with the Forms layout, etc.

Workaround

At the moment, I'm doing conversion to a MemoryStream in the native, eg in Android I have:

public class BuildQrCodes_Android : IBuildQrCodes
{
    public async Task<MemoryStream> ImageStreamForAsync(string text)
    {
        var writer = new BarcodeWriter 
            {
                Format = ZXing.BarcodeFormat.QR_CODE,
                Options = new EncodingOptions 
                    {
                        Height = 600,
                        Width = 600
                    }
            };

        var bitmap = writer.Write(text);

        var stream = new MemoryStream();
        await bitmap.CompressAsync(Bitmap.CompressFormat.Png, 100, stream);
        stream.Position = 0;

        return stream;
    }
}

and then over in the Xamarin Forms side, I have

IBuildQrCodes qrBuilder = /* Service lookup */
var stream = await qrBuilder.ImageStreamForAsync("the text to encode");
return ImageSource.FromStream(() => new MemoryStream(stream.ToArray()));

which is doing what I want, so it's an acceptable workaround.

Answer 1

I am not sure what widget "Content" in your code represents, but assigning your "image" to a Form View's Image Class that is a member of your ContentPage should do the trick.

In XAML, you would create an Image within your ContentPage, ie like in one of the Form's samples .

Otherwise, dynamically create an Image class widget, add it your layout via AddView for your ContentPage .