Trying to implement INotifyPropertyChanged in my own container.

BusinessRules.cs

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


namespace CS_3260_Lab_07
{
	/// <summary>
	/// This class will perform the background 'business' logic for our program.
	/// </summary>
	[Serializable]
	public sealed class BusinessRules : INotifyPropertyChanged
	{
		private SortedDictionary<uint, Employee>sortedEmployees = new SortedDictionary<uint, Employee>();

		// Create an event handler to track changes.
		public event PropertyChangedEventHandler PropertyChanged;
		public BusinessRules()
		{
		}
		
		// This method is called by the Set accessor of each property.
		// The CallerMemberName attribute that is applied to the optional propertyName
		// parameter causes the property name of the caller to be substituted as an argument.
		private void NotifyPropertyChanged( Employee emp )
		{
			PropertyChanged?.Invoke( this, new PropertyChangedEventArgs( emp.FirstName ) );
		}
		

		/// <summary>
		/// This method adds an employee to this container.
		/// Currently, this does not check for data validity (such as unique Employee ID numbers).
		/// </summary>
		/// <param name="toAdd">The Employee class object to add to this BusinessRules container.</param>
		public uint AddEmp( Employee toAdd )
		{
			if ( sortedEmployees.ContainsKey( toAdd.EmpID ) )
			{
				// Fail
				return 0;
			}
			else
			{
				// Add the passed object to our SortedDisctionary.
				sortedEmployees.Add( toAdd.EmpID, toAdd );
				return toAdd.EmpID;
			}
		}


		/// <summary>
		/// This method returns an employee class object located at the specified index.
		/// </summary>
		/// <param name="offset">The key into our SortedDictionary.</param>
		/// <returns>An Employee class object, if one exists at that location, otherwise null.</returns>
		public Employee GetEmp( uint offset )
		{
			// Check to make sure the requested location exists, and that it is not empty.
			if( sortedEmployees.ContainsKey( offset ) )
			{
				// Return the requested object.
				return sortedEmployees[offset];
			}
			else
			{
				// If we reach this code, the requested object does not exist.
				return null;
			}
		}


		/// <summary>
		/// This method just validates the existance of a key in our container.
		/// </summary>
		/// <param name="offset">The key to search for.</param>
		/// <returns></returns>
		public bool Contains( uint offset )
		{
			// Check to see if the key exists in our SortedDictionary.
			if ( sortedEmployees.ContainsKey( offset ) )
			{
				// Return true to indicate that the value exists as a key in our SortedDictionary.
				return true;
			}
			else
			{
				// Return false to indicate that the value does not exist as a key in our SortedDictionary.
				return false;
			}
		}
		
		
		/// <summary>
		/// This returns the number of Employee objects in this container.
		/// </summary>
		/// <returns>An integer representing the quantity of Employee objects in this container.</returns>
		public int Size()
		{
			// Return the count of objects in the SortedDictionary.
			return sortedEmployees.Count;
		}


		/// <summary>
		/// This method will remove an employee from the SortedDictionary that has the passed key.
		/// </summary>
		/// <param name="offset">The key of the employee to remove.</param>
		public void DeleteEmp( uint offset )
		{
			// If the employeeID exists in the SortedDictionary...
			if ( sortedEmployees.ContainsKey( offset ) )
			{
				//...remove the Employee class object from the SortedDictionary.
				sortedEmployees.Remove( offset );
			}
		}


		/// <summary>
		/// This will return every Employee class object in this container.
		/// </summary>
		/// <returns>A string containing all data for every Employee in this container.</returns>
		public override string ToString()
		{
			// Create a StringBuilder to hold all Employee information.
			System.Text.StringBuilder outString = new System.Text.StringBuilder();

			// Parse through every Employee and add it to our StringBuilder.
			foreach ( KeyValuePair<uint, Employee>employee in sortedEmployees )
			{
				// Append the Employee to our StringBuilder.
				outString.Append( employee.Value.ToString() );
			}
			// Return our StringBuilder, which now contains every Employee.
			return outString.ToString();
		}
	}
}