Dynamic grid row count and column count with XAML

using System.Windows;
using System.ComponentModel;

namespace GridHelperTest
{
  /// <summary>
  /// Interaction logic for MainWindow.xaml
  /// </summary>
  public partial class MainWindow : Window, INotifyPropertyChanged
  {
    public int RowCount { get; set; }
    public int ColumnCount { get; set; }

    public MainWindow ( )
    {
      InitializeComponent ();
      DataContext = this ;
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void TestButton_Click (object sender, RoutedEventArgs e)
    {
      MessageBox.Show ( "HELLO!", "Greetings", MessageBoxButton.OK, MessageBoxImage.Information );
    }

    private void CreateGrid_Click (object sender, RoutedEventArgs e)
    {
      if (int.TryParse ( rowSizeText.Text, out int rowResult ))
      {
        RowCount = rowResult;
        OnPropertyChanged("RowCount");
      }

      if (int.TryParse ( columnSizeText.Text, out int columnResult ))
      {
        ColumnCount = rowResult;
        OnPropertyChanged("ColumnCount");
      }
    }
    protected virtual void OnPropertyChanged(string propertyName = null)
    {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
  }
}

<Window x:Class="GridHelperTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:GridHelperTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="900" Width="800">

  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition Height="*"/>
      <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <Grid Grid.Row="0">
      <Label x:Name="colourName" Content="PURPLE" HorizontalAlignment="Left" Height="93" Margin="284,88,0,0" VerticalAlignment="Top" Width="243" FontWeight="Bold" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" FontSize="50" Foreground="#FFDC00FF"/>
      <Button x:Name="testButton" Content="Button" HorizontalAlignment="Left" Margin="354,234,0,0" VerticalAlignment="Top" Width="75" Click="TestButton_Click"/>
      <Label x:Name="label" Content="Row Size" HorizontalAlignment="Left" Margin="222,296,0,0" VerticalAlignment="Top" Foreground="#FFDC00FF"/>
      <Label x:Name="label_Copy" Content="Column Size" HorizontalAlignment="Left" Margin="438,296,0,0" VerticalAlignment="Top" Foreground="#FFDC00FF"/>
      <Button x:Name="createGrid" Content="Create Grid" HorizontalAlignment="Left" Margin="357,348,0,0" VerticalAlignment="Top" Width="75" Click="CreateGrid_Click"/>
      <TextBox x:Name="rowSizeText" HorizontalAlignment="Left" Height="23" Margin="296,299,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="62"/>
      <TextBox x:Name="columnSizeText" HorizontalAlignment="Left" Height="23" Margin="528,300,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="62"/>

    </Grid>
    <Grid Grid.Row="1"
          local:GridHelpers.RowCount="{Binding RowCount}"
          local:GridHelpers.ColumnCount="{Binding ColumnCount}">
      <Rectangle Grid.Row="0" Grid.Column="0" Fill="Red" Width="100" Height="100"/>
      <Rectangle Grid.Row="0" Grid.Column="1" Fill="Green" Width="100" Height="100"/>
      <Rectangle Grid.Row="1" Grid.Column="0" Fill="Blue" Width="100" Height="100"/>
      <Rectangle Grid.Row="1" Grid.Column="1" Fill="Yellow" Width="100" Height="100"/>

    </Grid>
  </Grid>
</Window>