GroupExpanderStateStore.cs

using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;

namespace NETworkManager.Controls
{
    public class GroupExpanderStateStore : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName) =>
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

        /// <summary>
        /// Stores the expansion state of each group by its name.
        /// </summary>
        private readonly Dictionary<string, bool> _states = [];

        /// <summary>
        /// The indexer to get or set the expansion state of a group by its name.
        /// </summary>
        /// <param name="groupName">Name of the group.</param>
        /// <returns>True if expanded, false if collapsed.</returns>
        public bool this[string groupName]
        {
            get
            {
                // Default to expanded if not set
                if (!_states.TryGetValue(groupName, out var val))
                    _states[groupName] = val = true;

                return val;
            }
            set
            {
                if (_states.TryGetValue(groupName, out var existing) && existing == value)
                    return;

                Debug.WriteLine("GroupExpanderStateStore: Setting state of '{0}' to {1}", groupName, value);

                _states[groupName] = value;
                OnPropertyChanged($"Item[{groupName}]");
            }
        }
    }
}