GazpromApp/ViewModels/MainWindowViewModel.cs

using CommunityToolkit.Mvvm.ComponentModel;
using GazpromApp.Messages;
using CommunityToolkit.Mvvm.Input;
using CommunityToolkit.Mvvm.Messaging;
using System.Collections.ObjectModel;
using System.Threading.Tasks;
using Avalonia.Controls;
using GazpromApp.Models;

namespace GazpromApp.ViewModels;

public partial class MainWindowViewModel : ViewModelBase
{
    public ObservableCollection<PointViewModel> Points { get; } = [];

    [RelayCommand]
    private async Task AddPoint()
    {
        PointViewModel? point = await WeakReferenceMessenger.Default.Send(new NewPointMessage());
        
        if (point != null)
            Points.Add(point);
        
        IsLineVisible = Points.Count > 0;
    }

    [RelayCommand]
    private async Task EditPoint(PointViewModel point)
    {
        PointViewModel p = await WeakReferenceMessenger.Default.Send(new EditPointMessage(point)) ?? point;
        Points[Points.IndexOf(point)] = p;
    }

    [RelayCommand]
    private void RemovePoint(PointViewModel point)
    {
        Points.Remove(point);
        
        IsLineVisible = Points.Count > 0;
    }
    
    // Visual properties
    
    [ObservableProperty]
    private bool _isLineVisible;

    public MainWindowViewModel()
    {
        if (Design.IsDesignMode)
            Points = [new PointViewModel(new Point()) { Name = "Name test", Description = "Description test" }];
        else Points = [];
    }
}