How to save a QR code created with ZXing on device gallery folder like image?

Hi, I have created an QR code with next code and show correctly in my app but I need to export it like an image on the gallery folder device. I don't know how to do it.

barcode = new ZXingBarcodeImageView
    {
            HorizontalOptions = LayoutOptions.FillAndExpand,
            VerticalOptions = LayoutOptions.FillAndExpand,
    };

barcode.BarcodeFormat = ZXing.BarcodeFormat.QR_CODE;
    barcode.BarcodeOptions.Width = 500;
    barcode.BarcodeOptions.Height = 500;
    barcode.BarcodeValue = card_code;
    QRCode.Content = barcode;

Thanks in advanced.