avaloniavalidation/AvaloniaValidationSample/Item.cs

using System;

namespace AvaloniaValidationSample;

public class Item
{
    public int Id { get; set; }
    private string _Password { get; set; }
    public string Password
    {
        get => _Password;
        set
        {
            validatePassword(value);
            _Password = value;
        }
    }

    public string Text { get; set; }

    private void validatePassword(string password)
    {
        if (password.Length < 3)
        {
            throw new ArgumentException(nameof(password), "Password length > 7 symbols");
        }
    }
}