const string tag = "progressToast";
const string group = "progressToastGroup";

new ToastContentBuilder()
    .AddArgument("action", "viewConversation")
    .AddArgument("conversationId", 423)
    .AddText("Sending image to conversation...")
    .AddVisualChild(new AdaptiveProgressBar()
    {
        Value = new BindableProgressBarValue("progress"),
        Status = "Sending..."
    })
    .Show(toast =>
    {
        toast.Tag = tag;
        toast.Group = group;

        toast.Data = new NotificationData(new Dictionary<string, string>()
        {
            { "progress", "0" }
        });
    });

double progress = 0;

while (progress < 1)
{
    await Task.Delay(new Random().Next(1000, 3000));

    progress += (new Random().NextDouble() * 0.15) + 0.1;

    ToastNotificationManagerCompat.CreateToastNotifier().Update(
        new NotificationData(new Dictionary<string, string>()
        {
            { "progress", progress.ToString() }
        }), tag, group);
}