DelegateWeakEventManager.shared.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.CompilerServices;
using static System.String;

namespace Xamarin.CommunityToolkit.Helpers
{
	/// <summary>
	/// Weak Delegate event manager that allows for garbage collection when the EventHandler is still subscribed
	/// </summary>
	public class DelegateWeakEventManager
	{
		readonly Dictionary<string, List<Subscription>> eventHandlers = new Dictionary<string, List<Subscription>>();

		/// <summary>
		/// Adds the event handler
		/// </summary>
		/// <param name="handler">Handler</param>
		/// <param name="eventName">Event name</param>
		public void AddEventHandler(Delegate? handler, [CallerMemberName] string eventName = "")
		{
			if (IsNullOrWhiteSpace(eventName))
				throw new ArgumentNullException(nameof(eventName));

			if (handler == null)
				throw new ArgumentNullException(nameof(handler));

			var methodInfo = handler.GetMethodInfo() ?? throw new NullReferenceException("Could not locate MethodInfo");

			EventManagerService.AddEventHandler(eventName, handler.Target, methodInfo, eventHandlers);
		}

		/// <summary>
		/// Removes the event handler.
		/// </summary>
		/// <param name="handler">Handler</param>
		/// <param name="eventName">Event name</param>
		public void RemoveEventHandler(Delegate? handler, [CallerMemberName] string eventName = "")
		{
			if (IsNullOrWhiteSpace(eventName))
				throw new ArgumentNullException(nameof(eventName));

			if (handler == null)
				throw new ArgumentNullException(nameof(handler));

			var methodInfo = handler.GetMethodInfo() ?? throw new NullReferenceException("Could not locate MethodInfo");

			EventManagerService.RemoveEventHandler(eventName, handler.Target, methodInfo, eventHandlers);
		}

		/// <summary>
		/// Invokes the event EventHandler
		/// </summary>
		/// <param name="sender">Sender</param>
		/// <param name="eventArgs">Event arguments</param>
		/// <param name="eventName">Event name</param>
		public void HandleEvent(object? sender, object eventArgs, string eventName) => RaiseEvent(sender, eventArgs, eventName);

		/// <summary>
		/// Invokes the event Action
		/// </summary>
		/// <param name="eventName">Event name</param>
		public void HandleEvent(string eventName) => RaiseEvent(eventName);

		/// <summary>
		/// Invokes the event EventHandler
		/// </summary>
		/// <param name="sender">Sender</param>
		/// <param name="eventArgs">Event arguments</param>
		/// <param name="eventName">Event name</param>
		public void RaiseEvent(object? sender, object eventArgs, string eventName) =>
			EventManagerService.HandleEvent(eventName, sender, eventArgs, eventHandlers);

		/// <summary>
		/// Invokes the event Action
		/// </summary>
		/// <param name="eventName">Event name</param>
		public void RaiseEvent(string eventName) => EventManagerService.HandleEvent(eventName, eventHandlers);
	}
}