wpftoolkit/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/PropertyGrid/Implementation/EditorDefinitionCollection.cs

using System;
using System.Linq;
using System.Collections.ObjectModel;

namespace Microsoft.Windows.Controls.PropertyGrid
{
    public class EditorDefinitionCollection : ObservableCollection<EditorDefinition>
    {
        public EditorDefinition this[string propertyName]
        {
            get
            {
                foreach (var item in Items)
                {
                    if (item.PropertiesDefinitions.Where(x => x.Name == propertyName).Any())
                        return item;
                }

                return null;
            }
        }

        public EditorDefinition this[Type targetType]
        {
            get
            {
                foreach (var item in Items)
                {
                    if (item.TargetType == targetType)
                        return item;
                }

                return null;
            }
        }
    }
}