double gridsplitters

Oh, you did not copy the Themes\Generic.xaml from my project to your project. This file contains the template of the Splitter, and my dragging code uses the rectangle in this template. Please copy the file into your project and include it in the project. Change the Generic.xaml code XMLNS as below:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:LWDMatch">

Sincerely,