XSDVisualizer/XSDVisualiser.Desktop/ViewModels/MainWindowViewModel.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using XSDVisualiser.Models;

namespace XSDVisualiser.Desktop.ViewModels
{
    public class MainWindowViewModel : INotifyPropertyChanged
    {
        private SchemaModel _model;
        private SchemaNode? _selectedRootElement;

        public MainWindowViewModel(SchemaModel model)
        {
            _model = model ?? throw new ArgumentNullException(nameof(model));
        }

        public event PropertyChangedEventHandler? PropertyChanged;

        private void OnPropertyChanged([CallerMemberName] string? name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }

        public SchemaModel Model
        {
            get => _model;
            set
            {
                if (!ReferenceEquals(_model, value))
                {
                    _model = value ?? throw new ArgumentNullException(nameof(value));
                    OnPropertyChanged();
                    OnPropertyChanged(nameof(RootElements));
                    OnPropertyChanged(nameof(VisibleRootElements));
                }
            }
        }

        public IEnumerable<SchemaNode> RootElements => _model?.RootElements ?? Enumerable.Empty<SchemaNode>();

        public SchemaNode? SelectedRootElement
        {
            get => _selectedRootElement;
            set
            {
                if (!EqualityComparer<SchemaNode?>.Default.Equals(_selectedRootElement, value))
                {
                    _selectedRootElement = value;
                    OnPropertyChanged();
                    OnPropertyChanged(nameof(VisibleRootElements));
                }
            }
        }

        public IEnumerable<SchemaNode> VisibleRootElements
        {
            get
            {
                if (SelectedRootElement != null)
                    return new[] { SelectedRootElement };
                return RootElements;
            }
        }
    }
}