PropertyGrid/Examples/QuickStartExample/MainWindow.axaml.cs

using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.LogicalTree;
using QuickStartExample.Models;

namespace QuickStartExample;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        var vehicle = new Vehicle();
        DataContext = vehicle;

        // Find the PropertyGrid and set its SelectedObject directly
        this.Opened += (s, e) =>
        {
            var propertyGrid = this.FindDescendantOfType<Avalonia.PropertyGrid.Controls.PropertyGrid>();
            if (propertyGrid != null)
            {
                propertyGrid.SelectedObject = vehicle;
                System.Diagnostics.Debug.WriteLine("PropertyGrid found and SelectedObject set directly");
            }
            else
            {
                System.Diagnostics.Debug.WriteLine("PropertyGrid NOT found!");
            }
        };
    }
}

public static class ControlExtensions
{
    public static T? FindDescendantOfType<T>(this Control control) where T : class
    {
        if (control is T result)
            return result;

        foreach (var child in control.GetLogicalChildren())
        {
            if (child is Control childControl)
            {
                var found = FindDescendantOfType<T>(childControl);
                if (found != null)
                    return found;
            }
        }

        return null;
    }
}