AddressModel.cs

using PostSharp.Patterns.Contracts;
using PostSharp.Patterns.Model;
using System;
using System.ComponentModel;
using System.Text;

namespace PostSharp.Samples.Xaml
{
  public class AddressModel : ModelBase
  {
    [DisplayName("Address Line 1")]
    [Required]
    public string Line1 { get; set; }

    [DisplayName("Address Line 2")]
    public string Line2 { get; set; }

    [Required]
    public string Town { get; set; }

    public string Country { get; set; }

    public DateTime Expiration { get; set; }

    [IgnoreAutoChangeNotification]
    public TimeSpan Lifetime => DateTime.Now - Expiration;

    [SafeForDependencyAnalysis]
    public string FullAddress
    {
      get
      {
        var stringBuilder = new StringBuilder();
        if (Line1 != null)
        {
          stringBuilder.Append(Line1);
        }

        if (Line2 != null)
        {
          if (stringBuilder.Length > 0)
          {
            stringBuilder.Append("; ");
          }

          stringBuilder.Append(Line2);
        }
        if (Town != null)
        {
          if (stringBuilder.Length > 0)
          {
            stringBuilder.Append("; ");
          }

          stringBuilder.Append(Town);
        }
        if (Country != null)
        {
          if (stringBuilder.Length > 0)
          {
            stringBuilder.Append("; ");
          }

          stringBuilder.Append(Country);
        }


        return stringBuilder.ToString();
      }
    }
  }
}