Do not show the items in the list after registration

Question

I’m taking a course in Xamarin and I stopped in the following item: I have two view, one to register a description of a food and a calorie value of this food. In the other view appears registered foods, or better should appear.

Hometabbedpage.Cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Reflection.Emit;
using System.Text;

using Xamarin.Forms;

namespace AluraNutricao
{
    public class HomeTabbedPage : TabbedPage
    {
        public HomeTabbedPage()
        {
            //criar uma lista de refeicoes ("lista ObservableCollection") que armazena o tipo Refeicao
            ObservableCollection<Refeicao> refeicoes = new ObservableCollection<Refeicao>();
            this.Children.Add(new CadastroRefeicao(refeicoes));
            this.Children.Add(new ListaRefeicoes(refeicoes));
        }
    }
}

Listarefeicoes.xaml.Cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;

namespace AluraNutricao
{
public partial class ListaRefeicoes : ContentPage
{
    public ObservableCollection<Refeicao> Refeicoes { get; private set; }

    public ListaRefeicoes(ObservableCollection<Refeicao> refeicoes)
    {
        Refeicoes = refeicoes;       

        BindingContext = this;

        InitializeComponent();
    }
    }
    }

Lists refeicoes.xaml

   <?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="AluraNutricao.ListaRefeicoes"
             Title="Lista Refeições">
  <ContentPage.Content>
      <StackLayout Padding ="25">
        <ListView ItemsSource="{Binding Refeicoes}">
          <ListView.ItemTemplate>
            <DataTemplate>
              <ViewCell>
                <ViewCell.View>
                  <StackLayout Padding="5" Spacing="1">
                    <Label Text="{Binding Teste}" FontSize="12" />
                    <StackLayout Orientation="Horizontal">
                      <Label Text="Calorias" FontSize="10" />
                      <Label Text="{Binding Calorias}" FontSize="10" />
                    </StackLayout>
                  </StackLayout>
                </ViewCell.View>
              </ViewCell>
            </DataTemplate>
          </ListView.ItemTemplate>
        </ListView>
      </StackLayout>    
    </ContentPage.Content>  
</ContentPage>

Refeicao.Cs

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="AluraNutricao.ListaRefeicoes"
         Title="Lista Refeições">
<ContentPage.Content>
  <StackLayout Padding ="25">
    <ListView ItemsSource="{Binding Refeicoes}">
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <ViewCell.View>
              <StackLayout Padding="5" Spacing="1">
                <Label Text="{Binding Teste}" FontSize="12" />
                <StackLayout Orientation="Horizontal">
                  <Label Text="Calorias" FontSize="10" />
                  <Label Text="{Binding Calorias}" FontSize="10" />
                </StackLayout>
              </StackLayout>
            </ViewCell.View>
          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>
  </StackLayout>    
  </ContentPage.Content>  
</ContentPage>

Criminal record.xaml

  <Label Text="Cadastro de refeição" FontSize="24" />

  <Entry x:Name="entDescricao" Placeholder="ex: File de frango" />

  <StackLayout Orientation="Horizontal">
    <Label Text="Calorias" />
    <Label Text=""  x:Name="lblCalorias" />
  </StackLayout>

  <Slider Minimum="0" Maximum="1000" x:Name="sldCalorias" 
   ValueChanged="UpdateCalorias"/>

  <Button Text="Cadastrar" Clicked="SalvaRefeicao" />

</StackLayout>
 </ContentPage.Content>
</ContentPage>

Cadastrorefeicao.xaml.Cs

    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.Linq;
     using System.Text;
    using System.Threading.Tasks;

    using Xamarin.Forms;

    namespace AluraNutricao
    {
    public partial class CadastroRefeicao : ContentPage
    {
        public ObservableCollection<Refeicao> refeicoes { get; set; }

        public CadastroRefeicao(ObservableCollection<Refeicao> refeicoes)
        {
            refeicoes = new ObservableCollection<Refeicao>();
            this.refeicoes = refeicoes;
            InitializeComponent();
        }

        //public CadastroRefeicao(ObservableCollection<Refeicao> refeicoes)
        //{
           // this.refeicoes = refeicoes;
       // }

        public void UpdateCalorias(Object sender, EventArgs e)
        {
            //pega valor do stepper
            double valor = sldCalorias.Value;
            lblCalorias.Text = valor.ToString();
        }

       public void SalvaRefeicao(Object sender, EventArgs e)
        {
            string descricao = entDescricao.Text;
            double valor = sldCalorias.Value;
            string calorias = sldCalorias.Value.ToString();

            if (descricao == "" || calorias=="0"){
                string msg = "Por favor, entrar com dados!";
                DisplayAlert("Cadastro de refeição", msg, "Ok");
            }
            else
            {
                Refeicao refeicao = new Refeicao(descricao, valor);
                refeicoes.Add(refeicao);
                string msg = "A refeição " + descricao + " de " + calorias + " calorias foi salva com sucesso";
                DisplayAlert("Cadastro de refeição", msg, "Ok");
                Clear();
            }

        }

        private void Clear()
        {
            entDescricao.Text = "";
            sldCalorias.Value = 0;
        }
    }
}

App.Cs

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    using Xamarin.Forms;

namespace AluraNutricao
{
    public class App : Application
    {
        public App()
        {
            // The root page of your application
            MainPage = new HomeTabbedPage();
        }

        protected override void OnStart()
        {
            // Handle when your app starts
        }

        protected override void OnSleep()
        {
            // Handle when your app sleeps
        }

        protected override void OnResume()
        {
            // Handle when your app resumes
        }
    }
}

Answer 1

Good afternoon, your code is a bit confusing but...

Your Binding is with the Refeicoes property that is filled through a constructor, put a break point in that constructor and see the moments when it is called and if there is record within the last parameter.

Answer 2

Another thing, you are instantiating the refections parameter within your Registry.

 public CadastroRefeicao(ObservableCollection<Refeicao> refeicoes)
    {
        refeicoes = new ObservableCollection<Refeicao>();
        this.refeicoes = refeicoes;
        InitializeComponent();
    }

Try to remove the section where you are instantiating:

 public CadastroRefeicao(ObservableCollection<Refeicao> refeicoes)
    {
        this.refeicoes = refeicoes;
        InitializeComponent();
    }