ZXing BarcodeWriter issue (string to barcode)

I am trying to create a QR code from a string and not having any luck with either ZXing.Net or ZXing.Net.Mobile.Forms.

I am trying this code with ZXing.Net.Mobile.Forms nuget package.

using System.ComponentModel;
using Xamarin.Forms;
using ZXing;

namespace ZXing {
    [DesignTimeVisible(true)]
    public partial class MainPage : ContentPage {
        public MainPage() {
            InitializeComponent();
            var writer = new BarcodeWriter();
            writer.Format = BarcodeFormat.QR_CODE;
            var barcode = writer.Write("test string");
            // etc
        }
    }
}

I keep getting an error with the red squiggles underneath BarcodeWriter();

Error CS0305 Using the generic type 'BarcodeWriter' requires 1 type arguments ZXing

I also tried the following with no luck

var writer = new ZXing.Mobile.BarcodeWriter();

I have copied the required lines into the Android MainActivity.cs OnCreate and OnRequestPermissionsResult methods. No iOS or UWP, just Android here.

I'm not sure how to remedy this error.