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();
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