An attached property to add spacing inside layout controls like stack-panels in WPF

SpacingSetter.cs

using System.Windows;
using System.Windows.Controls;

public class SpacingSetter
{
    public static readonly DependencyProperty SpacingProperty =
        DependencyProperty.RegisterAttached("Spacing", typeof(int), typeof(SpacingSetter),
            new UIPropertyMetadata(0, MarginChanged));

    public static int GetSpacing(DependencyObject dependencyObject)
    {
        return (int) dependencyObject.GetValue(SpacingProperty);
    }

    public static void SetSpacing(DependencyObject dependencyObject, int value)
    {
        dependencyObject.SetValue(SpacingProperty, value);
    }

    private static void MarginChanged(object sender, DependencyPropertyChangedEventArgs eventArgs)
    {
        if (sender is Panel panel)
        {
            panel.Loaded += PanelLoaded;
        }
    }

    private static void PanelLoaded(object sender, RoutedEventArgs eventArgs)
    {
        var panel = (Panel) sender;
        var firstIterate = true;

        foreach (var child in panel.Children)
        {
            if (child is FrameworkElement frameworkElement)
            {
                if (!firstIterate)
                {
                    frameworkElement.Margin = new Thickness(GetSpacing(panel), 0, 0, 0);
                }
                else
                {
                    firstIterate = false;
                }
            }
        }
    }
}