<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:DDP"
x:Class="DDP.MainPage"
BackgroundColor="#3f183d"
Title="My App Title">

<StackLayout BackgroundColor="Transparent" HeightRequest="70" HorizontalOptions="Start" VerticalOptions="Center" WidthRequest="1000">
    <local:AdMobView x:Name="adMobView" HorizontalOptions="FillAndExpand" VerticalOptions="EndAndExpand"/>
</StackLayout>
</ContentPage>

public MainPage()
    {
        InitializeComponent();

        BindingContext = this;
        adMobView.AdUnitId = AdMobView.codigoAdmob;
    }

using Xamarin.Forms;

namespace DDP
{
    public class AdMobView : View
{

public static readonly BindableProperty AdUnitIdProperty = BindableProperty.Create(
    nameof(AdUnitId),
    typeof(string),
    typeof(AdMobView),
    string.Empty);

public string AdUnitId
{
    get => (string)GetValue(AdUnitIdProperty);
    set => SetValue(AdUnitIdProperty, value);
}

//admob google test code
public static string codigoAdmob = "ca-app-pub-3940256099942544/6300978111";

}

using System.ComponentModel;
using DDP;
using DDP.Droid;
using Android.Content;
using Android.Gms.Ads;
using Android.Widget;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(AdMobView), typeof(AdMobViewRenderer))]
namespace DDP.Droid
{
    public class AdMobViewRenderer : ViewRenderer<AdMobView, AdView>
    {
        public AdMobViewRenderer(Context context) : base(context) { }

        protected override void         OnElementChanged(ElementChangedEventArgs<AdMobView> e)
    {
        base.OnElementChanged(e);

        if (e.NewElement != null && Control == null)
        {
            SetNativeControl(CreateAdView());
        }
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        if (e.PropertyName == nameof(AdView.AdUnitId))
            Control.AdUnitId = Element.AdUnitId;
    }

    private AdView CreateAdView()
    {
        var adView = new AdView(Context)
        {
            AdSize = AdSize.SmartBanner,
            AdUnitId = Element.AdUnitId
        };

        adView.LayoutParameters = new LinearLayout.LayoutParams(LayoutParams.MatchParent, LayoutParams.MatchParent);

        adView.LoadAd(new AdRequest.Builder().Build());

        return adView;
    }

}

//somecode

base.OnCreate(bundle);
MobileAds.Initialize(ApplicationContext, "ca-app-pub-3940256099942544/6300978111");
global::Xamarin.Forms.Forms.Init(this, bundle);
LoadApplication(new App());

//somecode