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using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms.CustomAttributes;
using Xamarin.Forms.Internals;
namespace Xamarin.Forms.Controls
{
[Preserve (AllMembers=true)]
[Issue (IssueTracker.Github, 1875, "NSRangeException adding items through ItemAppearing", PlatformAffected.iOS)]
public class Issue1875
: ContentPage
{
public Issue1875()
{
Button loadData = new Button { Text = "Load", HorizontalOptions = LayoutOptions.FillAndExpand };
ListView mainList = new ListView {
VerticalOptions = LayoutOptions.FillAndExpand,
HorizontalOptions = LayoutOptions.FillAndExpand
};
mainList.SetBinding (ListView.ItemsSourceProperty, "Items");
_viewModel = new MainViewModel ();
BindingContext = _viewModel;
loadData.Clicked += async (sender, e) => {
await LoadData ();
};
mainList.ItemAppearing += OnItemAppearing;
Content = new StackLayout {
Children = {
loadData,
mainList
}
};
}
readonly MainViewModel _viewModel;
int _start = 0;
const int NumberOfRecords = 15;
async void OnItemAppearing(object sender, ItemVisibilityEventArgs e)
{
var item = (int)e.Item;
if (!_viewModel.IsLoading && item == _viewModel.Items.Last())
await LoadData();
}
async Task LoadData ()
{
await _viewModel.LoadData (_start, NumberOfRecords);
_start = _start + NumberOfRecords;
}
public class MainViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public MainViewModel ()
{
}
ObservableCollection<int> _items;
public ObservableCollection<int> Items {
get {
if (_items == null)
_items = new ObservableCollection<int> ();
return _items;
}
set {
_items = value;
PropertyChanged (this, new PropertyChangedEventArgs ("Items"));
}
}
bool _isLoading;
public bool IsLoading {
get {
return _isLoading;
}
set {
if (_isLoading != value) {
_isLoading = value;
PropertyChanged (this, new PropertyChangedEventArgs ("IsLoading"));
}
}
}
#pragma warning disable 1998 // considered for removal
public async Task LoadData (int start, int numberOfRecords)
#pragma warning restore 1998
{
IsLoading = true;
for (int counter = 0; counter < numberOfRecords; counter++)
Items.Add (start + counter);
IsLoading = false;
}
}
}
}
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