How to create singleton class in Symbian

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Article

Created: savaj (07 Mar 2009)

Last edited: hamishwillee (26 Jul 2012)

See Also

• WSD and the Singleton Pattern
• How to create singleton class in Symbian
• Implementing a Singleton using Symbian CCoeStatic class

What is Singleton class?

A class whose number of instances that can be instantiated is limited to one is called a singleton class. Thus, at any given time only one instance can exist.

How to implement it in symbian?

Symbian provided CCoeStatic base class for creating singleton class. To omplement singleton pattern you have to derive your class from CCoeStatic class.

Header file

//MySingleton.h
#include <coemain.h>
 
class CMySingleton: public CCoeStatic
{
	public:
		static CMySingleton* GetInstance();
		~CMySingleton();
 
	private:
		CMySingleton();
		void InitializeL();
	public:
		void UpdateData(const TDesC8& aText);
		TInt iNumber;
}

Implementation file.

//MySingleton.cpp
static const TUid KUidMySingleton = { 0x10000123 };
 
CMySingleton* CMySingleton::GetInstance()
{
	CMySingleton* pInstance = (CMySingleton*)CCoeEnv::Static(KUidMySingleton);
	if (!pInstance)
	{
		pInstance = new (ELeave) CMySingleton();
		pInstance->InitializeL();
	}
 
	return pInstance;
}
 
CMySingleton::~CMySingleton()
{
}
 
CMySingleton::CMySingleton():CCoeStatic(KUidMySingleton)
{
}
 
void CMySingleton::InitializeL()
{
iNumber = 8; //initialize data member here.
}
 
void CMySingleton::UpdateData(const TDesC8& aText)
{
}

How to use it?

Add header file mysingleton.h in your class. And use it in following manner.
TBuf8<20> data( _L8("singleton") );
CMySingleton* pMySingleton = CMySingleton::GetInstance(); //if instance of class is available then it return it, else it will create new instance
pMySingleton->UpdateData(data)