How do I to create an infinite ListView in Xamarin?

Issue

I have many records on database, next to 5000 records on a table and to get this informations I am trying to use OFFSET and LIMIT at my webservice, it works well. On Xamarin I am trying to create an infinite ListView that will loading data while user make the scroll. The problem that I cannot do this works.

How do I to fix this ?

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"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             x:Class="MyApp.View.LimitOffsetTest">

    <ContentPage.Content>

        <StackLayout>            

            <ListView x:Name="MyList" ItemAppearing="OnItemAppearing" VerticalOptions="FillAndExpand">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <StackLayout>
                                <Label Text="{Binding numero}"></Label>
                                <Label Text="{Binding valor}"></Label>
                            </StackLayout>
                        </ViewCell>
                    </DataTemplate>
                </ListView.ItemTemplate>              

            </ListView>

            <StackLayout HorizontalOptions="FillAndExpand" BackgroundColor="Yellow">
                <Label x:Name="FooterLoading" Text="Loading..." IsVisible="False" TextColor="Red" FontAttributes="Bold" HorizontalOptions="Center"></Label>
            </StackLayout>

        </StackLayout>

    </ContentPage.Content>

</ContentPage>

LimitOffsetTest

public partial class LimitOffsetTest : ContentPage{
        private SmartCollection<NumerosSorteioDTO> smartCollection;

        private static ConcursoDTO _values = new ConcursoDTO();
        private static int OFFSET = 0;
        private const int LIMIT = 5;

        public LimitOffsetTest(){
            InitializeComponent();

            firstLoad();

        }

        private void firstLoad(){
            try{

                FooterLoading.IsVisible = true;

                smartCollection = new SmartCollection<NumerosSorteioDTO>();

                _values.offset = OFFSET;
                _values.limit = LIMIT;
                ConcursoDTO dto = ConcursoService.GetNumerosSorteConcursoLO(_values);
                smartCollection.AddRange(dto.numeros);
                this.BindingContext = smartCollection;
                this.MyList.ItemsSource = smartCollection;

            }catch(Exception e){
                Debug.WriteLine("Erro: " + e.Message);
            }
            finally{
                FooterLoading.IsVisible = false;
            }


        }

        private void OnItemAppearing(object sender, ItemVisibilityEventArgs args){

            try{
                FooterLoading.IsVisible = true;

                var _item = (NumerosSorteioDTO)args.Item;
                if (_item == smartCollection[smartCollection.Count - 1])
                {
                    _values.offset += 5;
                    ConcursoDTO dto = ConcursoService.GetNumerosSorteConcursoLO(_values);
                    smartCollection.AddRange(dto.numeros);
                }


            } catch(Exception e){
                Debug.WriteLine("Erro: " + e.Message);
            }finally{
                FooterLoading.IsVisible = false;
            }

        }




    }//class

Controller

public class SmartCollection<T> : ObservableCollection<T>
{
    public SmartCollection()
        : base()
    {
    }

    public SmartCollection(IEnumerable<T> collection)
        : base(collection)
    {
    }

    public SmartCollection(List<T> list)
        : base(list)
    {
    }

    public void AddRange(IEnumerable<T> range)
    {
        foreach (var item in range)
        {
            Items.Add(item);
        }

        this.OnPropertyChanged(new PropertyChangedEventArgs("Count"));
        this.OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
        this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }

    public void Reset(IEnumerable<T> range)
    {
        this.Items.Clear();

        AddRange(range);
    }
}

Solution

I use your code and add some local data, your codes works well on my side. You should check whether ConcursoService.GetNumerosSorteConcursoLO get the right data:

ConcursoDTO dto = ConcursoService.GetNumerosSorteConcursoLO(_values);

Here is some part of my codes:

private void OnItemAppearing(object sender, ItemVisibilityEventArgs args)
{
    try
    {
        FooterLoading.IsVisible = true;

        var _item = (NumerosSorteioDTO)args.Item;
        if (_item == smartCollection[smartCollection.Count - 1])
        {
            _values.offset += 5;
            //ConcursoDTO dto = ConcursoService.GetNumerosSorteConcursoLO(_values);
            NumerosSorteioDTO obj1 = new NumerosSorteioDTO { numero = "1", valor = "1" };
            NumerosSorteioDTO obj2 = new NumerosSorteioDTO { numero = "2", valor = "2" };
            NumerosSorteioDTO obj3 = new NumerosSorteioDTO { numero = "3", valor = "3" };
            NumerosSorteioDTO obj4 = new NumerosSorteioDTO { numero = "4", valor = "4" };
            NumerosSorteioDTO obj5 = new NumerosSorteioDTO { numero = "5", valor = "5" };

            ConcursoDTO dto = new ConcursoDTO();
            dto.numeros.Add(obj1);
            dto.numeros.Add(obj2);
            dto.numeros.Add(obj3);
            dto.numeros.Add(obj4);
            dto.numeros.Add(obj5);

            smartCollection.AddRange(dto.numeros);
        }
    }
    catch (Exception e)
    {
        Debug.WriteLine("Erro: " + e.Message);
    }
    finally
    {
        FooterLoading.IsVisible = false;
    }
}

I uploaded my test project here and you can check.

Here is the result:

Answered By - nevermore