Object Oriented Programming Patterns for Geeks

The Memento Pattern

namespace ooppatterns
{
    using System;
    using System.Collections.Generic;
    using System.Reflection;

    internal class Program
    {
        private static void Main( string[] args )
        {
            CustomerData CD = new CustomerData( "Mr", "Matt", "Warren" );

            CD.Email = "matt@foo.com";

            Memento<CustomerData> mem = new Memento<CustomerData>();
            //try
            //{
            // temporaily store object
            mem.Store( CD );

            // Attempt update
            CD.Email = "fizz@bang.com";

            // if there are no errors... continue...
            //}
            //catch
            //{
            // If there is an error, restore object to previous state
            mem.Restore( CD );
            //}

            Console.WriteLine();

            //try
            //{
            // temporaily store object
            CD.Store( mem );

            // Attempt update
            CD.Email = "someone@somewhere.com";

            // if there are no errors... continue...
            //}
            //catch
            //{
            // If there is an error, restore object to previous state
            CD.Restore( mem );
            //}

            Console.ReadLine();
        }
    }

    interface IStorable<T>
        where T : class
    {
        void Store( Memento<T> item );

        void Restore( Memento<T> item );
    }

    class Memento<T>
        where T : class
    {
        private const BindingFlags BINDINGS 
            = BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public;
        private Dictionary<int, Dictionary<string, object>> _storeage;

        public Memento()
        {
            this._storeage = new Dictionary<int, Dictionary<string, object>>();
        }

        public void Store( T item )
        {
            if ( this._storeage.ContainsKey( item.GetHashCode() ) )
                throw new InvalidOperationException( 
                        "Object supplied is already stored!" );

            Dictionary<string, object> _data = new Dictionary<string, object>();

            FieldInfo[] FIs = typeof( T ).GetFields( BINDINGS );

            foreach ( FieldInfo FI in FIs )
                _data.Add( FI.Name, FI.GetValue( item ) );

            this._storeage.Add( item.GetHashCode(), _data );

            Console.WriteLine( " OBJECT STATE STORED : {0}", item.ToString() );
        }

        public void Restore( T item )
        {
            if ( !this._storeage.ContainsKey( item.GetHashCode() ) )
                throw new InvalidOperationException( 
                        "Object supplied is does not have any stored data!" );

            Console.WriteLine( "STATE BEFORE RESTORE : {0}", item.ToString() );

            Dictionary<string, object> _data = this._storeage[item.GetHashCode()];

            foreach ( string field in _data.Keys )
            {
                FieldInfo FI = typeof( T ).GetField( field, BINDINGS );

                FI.SetValue( item, _data[field] );
            }

            this._storeage.Remove( item.GetHashCode() );

            Console.WriteLine( " STATE AFTER RESTORE : {0}", item.ToString() );
        }
    }

    class CustomerData : IStorable<CustomerData>
    {
        private string _title = @"";
        private string _forename = @"";
        private string _surname = @"";
        private string _email = @"";
        private string _phone = @"";
        private string _cellular = @"";

        public CustomerData( string title, string forename, string surname )
        {
            this._title = title;
            this._forename = forename;
            this._surname = surname;
        }

        public string Title
        {
            get { return this._title; }
            set { this._title = value; }
        }

        public string Forename
        {
            get { return this._forename; }
            set { this._forename = value; }
        }

        public string Surname
        {
            get { return this._surname; }
            set { this._surname = value; }
        }

        public string Email
        {
            get { return this._email; }
            set { this._email = value; }
        }

        public string Phone
        {
            get { return this._phone; }
            set { this._phone = value; }
        }

        public string Cellular
        {
            get { return this._cellular; }
            set { this._cellular = value; }
        }

        // Store data...
        public void Store( Memento<CustomerData> item )
        {
            item.Store( this );
        }

        // Restore data
        public void Restore( Memento<CustomerData> item )
        {
            item.Restore( this );
        }

        public override string ToString()
        {
            return string.Format( "{0} {1} {2}, {3} {4} {5}", 
                  this._title, this._forename, this._surname, 
                  this._email, this._phone, this._cellular );
        }
    }
}