Object Oriented Programming Patterns for Geeks

A Simple Factory

The basic idea to factories is that they create objects for you. 

The simplest example is given here:

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

    internal class Program
    {
        private static void Main( string[] args )
        {
            List<IDoSomething> aList = new List<IDoSomething>();

            SimpleMethodFactory factory = new SimpleMethodFactory();

            for ( int i = 0; i < 32; i++ )
                aList.Add( factory.Create( i ) );

            foreach ( IDoSomething ID in aList )
                Console.WriteLine( ID.DoSomething );

            Console.ReadLine();
        }
    }

    // product
    interface IDoSomething
    {
        string DoSomething { get; }
    }

    // Concrete Creator
    class SimpleMethodFactory
    {
        /// <summary>
        /// Manufactures and object based on criteria.
        /// </summary>
        /// <param name="manufactureCriteria">The manufacture criteria.</param>
        /// <returns>An IDoSomething derived object</returns>
        public IDoSomething Create( int manufactureCriteria )
        {
            if ( manufactureCriteria % 15 == 0 )
                return new Example01( "This is created using MOD 15  FIZZBANG" );

            if ( manufactureCriteria % 5 == 0 )
                return new Example02( "This is created using MOD 5   FIZZ" );

            if ( manufactureCriteria % 3 == 0 )
                return new Example03( "This is created using MOD 3   BANG" );

            return new Example00( manufactureCriteria.ToString() );
        }
    }

    // Concrete Product 00
    class Example00 : IDoSomething
    {
        private string _value;

        public Example00( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example00 : {0}", this._value ); }
        }
    }

    // Concrete Product 01
    class Example01 : IDoSomething
    {
        private string _value;

        public Example01( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example01 : {0}", this._value ); }
        }
    }

    // Concrete Product 02
    class Example02 : IDoSomething
    {
        private string _value;

        public Example02( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example02 : {0}", this._value ); }
        }
    }

    // Concrete Product 03
    class Example03 : IDoSomething
    {
        private string _value;

        public Example03( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example03 : {0}", this._value ); }
        }
    }
}

Another take for GoF purists:

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

    internal class Program
    {
        private static void Main( string[] args )
        {
            SimpleMethodFactoryBase[] factories = 
            {
                new SimpleMethodFactoryA(),
                new SimpleMethodFactoryB()
            };

            List<IDoSomething> aList = new List<IDoSomething>();

            for ( int i = 0; i < 32; i++ )
                aList.Add( factories[1-(i % 2)].Create( i ) );

            foreach ( IDoSomething ID in aList )
                Console.WriteLine( ID.DoSomething );

            Console.ReadLine();
        }
    }

    // Product
    interface IDoSomething
    {
        string DoSomething { get; }
    }

    // Creator
    abstract class SimpleMethodFactoryBase
    {
        /// <summary>
        /// Manufactures and object based on criteria.
        /// </summary>
        /// <param name="manufactureCriteria">The manufacture criteria.</param>
        /// <returns>An IDoSomething derived object</returns>
        public abstract IDoSomething Create( int manufactureCriteria );
    }

    // Concrete Creator A
    class SimpleMethodFactoryA : SimpleMethodFactoryBase
    {
        public override IDoSomething Create( int manufactureCriteria )
        {
            if ( manufactureCriteria % 15 == 0 )
                return new Example01( "This is created using MOD 15  FIZZBANG" );

            if ( manufactureCriteria % 5 == 0 )
                return new Example02( "This is created using MOD 5   FIZZ" );

            if ( manufactureCriteria % 3 == 0 )
                return new Example03( "This is created using MOD 3   BANG" );

            return new Example00( manufactureCriteria.ToString() );
        }
    }

    // Concrete Creator B
    class SimpleMethodFactoryB : SimpleMethodFactoryBase
    {
        public override IDoSomething Create( int manufactureCriteria )
        {
            if ( manufactureCriteria % 13 == 0 )
                return new Example03( "This is created using MOD 13  Wibble" );

            if ( manufactureCriteria % 10 == 0 )
                return new Example01( "This is created using MOD 10  Wobble" );

            if ( manufactureCriteria % 7 == 0 )
                return new Example02( "This is created using MOD 7   Wubble" );

            return new Example00( manufactureCriteria.ToString() );
        }
    }

    // Concrete Product 00
    class Example00 : IDoSomething
    {
        private string _value;

        public Example00( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example00 : {0}", this._value ); }
        }
    }

    // Concrete Product 01
    class Example01 : IDoSomething
    {
        private string _value;

        public Example01( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example01 : {0}", this._value ); }
        }
    }

    // Concrete Product 02
    class Example02 : IDoSomething
    {
        private string _value;

        public Example02( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example02 : {0}", this._value ); }
        }
    }

    // Concrete Product 03
    class Example03 : IDoSomething
    {
        private string _value;

        public Example03( string value )
        {
            this._value = value;
        }

        public string DoSomething
        {
            get { return string.Format( "Example03 : {0}", this._value ); }
        }
    }
}