Singleton Design Pattern

This design pattern is come under Creational Pattern in .Net. It is pattern is one of the simplest design patterns. This pattern ensures that a class has only one instance.Make the class of the single instance object responsible for creation, initialization, access, and enforcement. Declare the instance as a private static data member. Provide a public static member function that encapsulates all initialization code, and provides access to the instance. We can use the pattern for creating / controlled access for an object. The below example shows the implementation for this one.
Real time usage
Dbconnection , Utility projects, etc.
Example

       // .NET guarantees thread safety for static initialization

        private static SingletonConnaction instance = null;

        SqlConnection sqlConnection = null;

       

        private SingletonConnaction()

        {

            //To DO: Remove below line

            Console.WriteLine("Singleton Instance ");

            Console.WriteLine("-----------------");

           

            //Replace the Connection string by the below string.

            sqlConnection = new SqlConnection();

        }

        // Lock synchronization object

        private static object syncLock = new object();

       

        /// <summary>

        /// DB Connection Object.

        /// </summary>

        public static SingletonConnaction DBConnection

        {

            get

            {

                // Support multithreaded applications through

                lock (syncLock)

                {

                    if (SingletonConnaction.instance == null)

                        SingletonConnaction.instance = new SingletonConnaction();

                    return SingletonConnaction.instance;

                }

            }

        }

 

        public void Connect()

        {

            Console.WriteLine("Connect.......!");

        }

 

        public void Disconnect()

        {

            sqlConnection.Dispose();

            instance = null;

 

            Console.WriteLine("DisConnect.......!");

        }

We can call this method from one main function .You can see the object created only the instance became null.

//Connecting to SQL/Initialize SQL Connection

            SingletonConnaction.DBConnection.Connect();

            //Reuse Existing Connection

            SingletonConnaction.DBConnection.Connect();

            //Disconnecting Connection

            SingletonConnaction.DBConnection.Disconnect();

            //ReConnecting to SQL/ReInitialize SQL Connection

            SingletonConnaction.DBConnection.Connect();

            SingletonConnaction.DBConnection.Disconnect();

            Console.ReadLine();

Output:
Singleton Instance
---------------------------
Connect………….!
Connect………….!
Disconnect………….!
Singleton Instance
---------------------------
Connect………….!
Disconnect………….!