Singleton

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Oct 11, 2013

CPOL

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Singleton The Singleton Design Pattern ensures that only a single instance of a given object can exist.It does this by making the class

Singleton

The Singleton Design Pattern ensures that only a single instance of a given object can exist.

It does this by making the class constructor private so that it [the singleton itself] has full control over when the class instance is created. In order to gain access to an instance of a class that implements the Singleton pattern, the developer must call a shared/static method of that Singleton class.

A VB example of a Singleton

Public Class SingletonSample
 
    'shared members
    Private Shared _instance As New SingletonSample
 
    Public Shared Function Instance() As SingletonSample
        Return _instance
    End Function
 
    'instance members
    Private Sub New()
        'public instantiation disallowed
    End Sub
 
    'other instance members
    '...
 
End Class

A C# example of a Singleton

public class SingletonSample
{
    //shared members
    private static SingletonSample _instance = new SingletonSample();
 
    public static SingletonSample Instance()
    {
        return _instance;
    }
 
    //instance members
    private SingletonSample()
    {
        //public instantiation disallowed
    }
 
    //other instance members
    //...
}

With the Singleton Design Pattern in place, the developer can easily access that single object instance without needing to worry about inadvertently creating multiple instances, and provides a global point of access to it.

VB - Dim mySingleton As SingletonSample = SingletonSample.Instance

C# - SingletonSample mySingleton = SingletonSample.Instance();