Any way to determine when the last listboxitem comes into view?

Question

I am new to windows phone and coming from an ios background. My question is, how can i programmatically determine when the last listboxitem comes into view? I am currently using a custom listboxitem and programmatically adding each item.

Answer 1

In most scenarios on Windows Phone 8 it's better to use the LongListSelector instead of the ListBox control.

Instead of loading all the items at once, the LongListSelector virtualizes its content, only loading data as needed to show in its viewport.

The ItemRealized event fires when a new item is assigned a UI container (realized). Use this event to determine if you are close to the end of the items in the datasource, then load more data.

XAML

<phone:LongListSelector x:Name='longListFlights'
                        ItemsSource='{Binding}'
                        ItemRealized='longListFlights_ItemRealized'
                        Height='205'
                        Margin='20'>
  <phone:LongListSelector.ItemTemplate>
    <DataTemplate>

      <StackPanel Orientation='Horizontal'>
        <TextBlock Text='{Binding FlightNumber}'
                     Foreground='Yellow' />

        <TextBlock Text='{Binding TimeStamp}'
                     Margin='20,0,0,0' />
      </StackPanel>
    </DataTemplate>
  </phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>

CODE

public partial class MainPage : PhoneApplicationPage {
    private ObservableCollection<Flight> _flights = 
                         new ObservableCollection<Flight>();
    private bool _isLoadingData;

    public MainPage() {
      InitializeComponent();

      AddFlights(60);
      this.DataContext = _flights;
    }

    private void AddFlights(int numberFlightsToAdd) {
      _isLoadingData = true;
      int max = _flights.Count + numberFlightsToAdd;
      for (int i = _flights.Count; i < max; i++)
      {
        _flights.Add(new Flight { FlightNumber = string.Format("AB-{0:D3}", i),
                                  TimeStamp = DateTime.Now });
      }
      _isLoadingData = false;
    }

    private void longListFlights_ItemRealized(object sender, 
                                              ItemRealizationEventArgs e) {

      Flight flight = e.Container.Content as Flight;
       if (flight != null)
      {
        if (!_isLoadingData)
        {
          // get current count of data-source
          int count = _flights.Count;

          // get index of item being realized (placed in container)
          int index = _flights.IndexOf(flight);

          // if we are close to the end, load more data
          if (count - index <= 5)
          {
            AddFlights(10);
          }
        }
        Console.WriteLine(flight.FlightNumber);
      }
    }
  }

  internal class Flight {

    public string FlightNumber { get; set; }
    public DateTime TimeStamp { get; set; }
  }
}

Screenshot