Avalonia/samples/ControlCatalog/ViewModels/ItemsRepeaterPageViewModel.cs

using System;
using System.Collections.ObjectModel;
using System.Linq;
using Avalonia.Media;
using MiniMvvm;

namespace ControlCatalog.ViewModels
{
    public class ItemsRepeaterPageViewModel : ViewModelBase
    {
        private int _newItemIndex = 1;
        private int _newGenerationIndex = 0;
        private ObservableCollection<ItemsRepeaterPageViewModelItem> _items;

        public ItemsRepeaterPageViewModel()
        {
            _items = CreateItems();
        }

        public ObservableCollection<ItemsRepeaterPageViewModelItem> Items
        {
            get => _items;
            set => this.RaiseAndSetIfChanged(ref _items, value);
        }

        public ItemsRepeaterPageViewModelItem? SelectedItem { get; set; }

        public void AddItem()
        {
            var index = SelectedItem != null ? Items.IndexOf(SelectedItem) : -1;
            Items.Insert(index + 1, new ItemsRepeaterPageViewModelItem(index + 1, $"New Item {_newItemIndex++}"));
        }

        public void RemoveItem()
        {
            if (SelectedItem is not null)
            {
                Items.Remove(SelectedItem);
                SelectedItem = null;
            }
            else if (Items.Count > 0)
            {
                Items.RemoveAt(Items.Count - 1);
            }
        }

        public void RandomizeHeights()
        {
            var random = new Random();

            foreach (var i in Items)
            {
                i.Height = random.Next(240) + 10;
            }
        }

        public void ResetItems()
        {
            Items = CreateItems();
        }

        private ObservableCollection<ItemsRepeaterPageViewModelItem> CreateItems()
        {
            var suffix = _newGenerationIndex == 0 ? string.Empty : $"[{_newGenerationIndex.ToString()}]";

            _newGenerationIndex++;

            return new ObservableCollection<ItemsRepeaterPageViewModelItem>(
                Enumerable.Range(1, 100000).Select(i => new ItemsRepeaterPageViewModelItem(i, $"Item {i.ToString()} {suffix}")));
        }
    }
    
    public class ItemsRepeaterPageViewModelItem : ViewModelBase
    {
        private double _height = double.NaN;

        public ItemsRepeaterPageViewModelItem(int index, string text)
        {
            Index = index;
            Text = text;
        }
        public int Index { get; }
        public string Text { get; }
            
        public double Height 
        {
            get => _height;
            set => this.RaiseAndSetIfChanged(ref _height, value);
        }
    }
}