<?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:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="XF_FirebaseStorage.MainPage">

    <StackLayout>
        <StackLayout>
            <StackLayout HorizontalOptions="Center" VerticalOptions="Start">

                <Image Margin="0,0,0,10" HeightRequest="100" Source="firebase.png" ></Image>
                <Label Margin="0,0,0,10" Text="Firebase Storage" FontAttributes="Bold" 
                       FontSize="Large" TextColor="Gray" HorizontalTextAlignment="Center" />
                <Image x:Name="imagemSelecionada" HeightRequest="150"></Image>
                <Entry x:Name="txtNomeArquivo" Placeholder="Nome do arquivo"></Entry>

                <StackLayout  HorizontalOptions="CenterAndExpand" Orientation="Horizontal">
                    <Button x:Name="btnPega" WidthRequest="200" Text="Pegar Imagem" 
                                Clicked="BtnSelecionaImagem_Clicked"/>
                    <Button x:Name="btnUpload" WidthRequest="200" Text="Enviar Imagem" 
                                Clicked="BtnUpload_Clicked" />
                </StackLayout>

                <StackLayout HorizontalOptions="CenterAndExpand" Orientation="Horizontal">
                    <Button x:Name="btnDownload" WidthRequest="200" Text="Download" 
                                  Clicked="btnDownload_Clicked" />
                    <Button x:Name="btnDeleta" WidthRequest="200" Text="Deletar Imagem" 
                                  Clicked="btnDeleta_Clicked" />
                </StackLayout>

                <Label x:Name="lblPath"></Label>
            </StackLayout>
        </StackLayout>
    </StackLayout>

</ContentPage>

using Firebase.Storage;
using System;
using System.IO;
using System.Threading.Tasks;

namespace XF_FirebaseStorage.Services
{
    public class FirebaseStorageService
    {
        FirebaseStorage firebaseStorage = new FirebaseStorage("xamarinimag******o***");

        public async Task<string> UploadFile(Stream fileStream, string fileName)
        {
            try
            {
                var imageUrl = await firebaseStorage
                    .Child("Paisagens")
                    .Child(fileName)
                    .PutAsync(fileStream);
                return imageUrl;
            }
            catch(Exception ex)
            {
                throw ex;
            }
        }

        public async Task<string> GetFile(string fileName)
        {
            try
            {
                return await firebaseStorage
                    .Child("Paisagens")
                    .Child(fileName)
                    .GetDownloadUrlAsync();
            }
            catch(Exception)
            {
                throw;
            }
        }
        public async Task DeleteFile(string fileName)
        {
            try
            {
                await firebaseStorage
                     .Child("Paisagens")
                     .Child(fileName)
                     .DeleteAsync();
            }
            catch (Exception)
            {
                throw;
            }
        }
    }
}

using Plugin.Media;
using Plugin.Media.Abstractions;
using System;
using System.ComponentModel;
using System.IO;
using Xamarin.Forms;
using XF_FirebaseStorage.Services;

namespace XF_FirebaseStorage
{
    [DesignTimeVisible(false)]
    public partial class MainPage : ContentPage
    {
        FirebaseStorageService fbStorageService = new FirebaseStorageService();
        MediaFile arquivoMediaFile;

        public MainPage()
        {
            InitializeComponent();
        }

        private async void BtnSelecionaImagem_Clicked(object sender, EventArgs e)
        {
            await CrossMedia.Current.Initialize();
            try
            {
                arquivoMediaFile = await Plugin.Media.CrossMedia.Current.PickPhotoAsync(
                        new Plugin.Media.Abstractions.PickMediaOptions
                {
                    PhotoSize = Plugin.Media.Abstractions.PhotoSize.Medium
                });
                

                if (arquivoMediaFile == null)
                    return;

                imagemSelecionada.Source = ImageSource.FromStream(() =>
                {
                    var imageStram = arquivoMediaFile.GetStream();
                    return imageStram;
                });
            }
            catch (Exception ex)
            {
                await DisplayAlert("Sucesso", ex.Message, "OK");
            }
        }

        private async void BtnUpload_Clicked(object sender, EventArgs e)
        {

            if (arquivoMediaFile == null)
            {
                await DisplayAlert("Erro", "Erro ao selecionar imagem.", "OK");
                return;
            }
            else
            {
                await fbStorageService.UploadFile(arquivoMediaFile.GetStream(), 
                              Path.GetFileName(arquivoMediaFile.Path));
                await DisplayAlert("Sucesso", "Imagem enviada ao Storage com sucesso.", "OK");
            }
        }

        private async void btnDownload_Clicked(object sender, EventArgs e)
        {
            string path = await fbStorageService.GetFile(txtNomeArquivo.Text);
            if (path != null)
            {
                lblPath.Text = path;
                await DisplayAlert("Sucesso", "Arquivo :  " + path + "  baixado", "OK");
            }
        }

        private async void btnDeleta_Clicked(object sender, EventArgs e)
        {
            await fbStorageService.DeleteFile(txtNomeArquivo.Text);
            lblPath.Text = string.Empty;
            await DisplayAlert("Sucesso", "Deletado", "OK");
        }
    }