namespace NinjaTrader.NinjaScript.AddOns
{
    public class TestWPFWindowSelector : System.Windows.Controls.WpfPropertyGrid.PropertyEditor
    {
        public TestWPFWindowSelector()
        {
            InlineTemplate = CreateTemplate();
        }

        System.Windows.DataTemplate CreateTemplate()
        {
            const string xamlTemplate = @"
<DataTemplate >
      <Grid>
        <Grid.ColumnDefinitions>
          <ColumnDefinition Width=""30""/>
          <ColumnDefinition Width=""*""/>
        </Grid.ColumnDefinitions>

    <Button Grid.Column=""0"" Content=""..."" Padding=""0"" Margin=""0""
              HorizontalAlignment=""Stretch"" VerticalAlignment=""Stretch""
              HorizontalContentAlignment=""Center""
              Style=""{x:Null}""
              Command =""pg:PropertyEditorCommands.ShowDialogEditor""
              CommandParameter=""{Binding}"" />

        <TextBox Grid.Column=""1""
                 Text=""{Binding StringValue}""
                 ToolTip=""{Binding Value}""/>


      </Grid>
    </DataTemplate>
";

            System.Windows.Markup.ParserContext context = new System.Windows.Markup.ParserContext();
            context.XmlnsDictionary.Add("", "http://schemas.microsoft.com/winfx/2006/xaml/presentation");
            context.XmlnsDictionary.Add("x", "http://schemas.microsoft.com/winfx/2006/xaml");
            context.XmlnsDictionary.Add("pg", "http://schemas.denisvuyka.wordpress.com/wpfpropertygrid");
            System.Windows.DataTemplate template = (System.Windows.DataTemplate)System.Windows.Markup.XamlReader.Parse(xamlTemplate, context);
            return template;
        }

        public override void ClearValue(System.Windows.Controls.WpfPropertyGrid.PropertyItemValue propertyValue, System.Windows.IInputElement commandSource)
        {
            if (propertyValue == null || propertyValue.IsReadOnly)
            {
                return;
            }
            propertyValue.StringValue = string.Empty;
        }

        public override void ShowDialog(System.Windows.Controls.WpfPropertyGrid.PropertyItemValue propertyValue, System.Windows.IInputElement commandSource)
        {
            System.Windows.Controls.WpfPropertyGrid.PropertyGrid propGrid = commandSource as System.Windows.Controls.WpfPropertyGrid.PropertyGrid;
            if (propGrid == null) return;

            NinjaTrader.Gui.Tools.NTWindow myWindow = new NinjaTrader.Gui.Tools.NTWindow();
            myWindow.Width = 100;
            myWindow.Height = 100;
            myWindow.WindowStartupLocation = System.Windows.WindowStartupLocation.CenterOwner;
            bool? result = myWindow.ShowDialog();
            propertyValue.StringValue = "success"; // change this string and compile, the ui does not see this change
            propGrid.DoReload();
            propGrid.RaiseEvent(new System.Windows.Controls.WpfPropertyGrid.PropertyValueChangedEventArgs(System.Windows.Controls.WpfPropertyGrid.PropertyGrid.PropertyValueChangedEvent, propertyValue.ParentProperty, ""));
        }
    }
}

//*********************************************************************************************************************************
Use in a script:

[Display(Name = "TestProperty", GroupName = "Test")]
[PropertyEditor("NinjaTrader.NinjaScript.AddOns.TestWPFWindowSelector")]
public string TestProperty { get; set; }