GazpromApp/Views/MainWindow.axaml.cs

using Avalonia.Controls;
using GazpromApp.Messages;
using GazpromApp.ViewModels;
using CommunityToolkit.Mvvm.Messaging;

namespace GazpromApp.Views;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        if (Design.IsDesignMode)
            return;

        WeakReferenceMessenger.Default.Register<MainWindow, NewPointMessage>(this, static (w, m) =>
        {
            NewPointDialog dialog = new NewPointDialog()
            {
                DataContext = new NewPointDialogViewModel()
            };
            m.Reply(dialog.ShowDialog<PointViewModel?>(w));
        });
        
        WeakReferenceMessenger.Default.Register<MainWindow, EditPointMessage>(this, static (w, m) =>
        {
            EditPointDialog dialog = new EditPointDialog()
            {
                DataContext = new EditPointDialogViewModel(m.Point)
            };
            m.Reply(dialog.ShowDialog<PointViewModel?>(w));
        });
    }
}