AvaloniaProject/AvaloniaApplication4/Views/MessageBox.axaml.cs

using Avalonia.Controls;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Interactivity;
using AvaloniaApplication4.ViewModels;

namespace AvaloniaApplication4.Views
{
    public partial class MessageBox : Window
    {
        public MessageBox(string Message)
        {
            InitializeComponent();
            message.Text = Message;
        }
    }
}