How +to create a singleton

diff -r 51a74ef9ed63 -r ae94777fff8f Symbian3/SDK/Source/GUID-7250950C-5502-5ACE-864B-0EFD5C253053.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/SDK/Source/GUID-7250950C-5502-5ACE-864B-0EFD5C253053.dita Fri Jun 11 12:39:03 2010 +0100 @@ -0,0 +1,76 @@ + + + + + +How +to create a singleton +

The CCoeStatic class allows singleton classes to be +created and stored by the environment (CCoeEnv) in Thread +Local Storage (TLS). This provides a means of creating writeable global static +data.

MySingleton.h

+ +class CMySingleton : public CCoeStatic + { +public: + static CMySingleton* SelfL() ; // Slightly slower + static CMySingleton* SelfL( CCoeEnv* aCoeEnv ) ; // Slightly faster + ... +private: + CMySingleton() ; + ~CMySingleton() ; + } ; + +

MySingleton.cpp

+ +const TUid KUidMySingleton = {0x10204232} ; + +CMySingleton::CMySingleton() : CCoeStatic( KUidMySingleton, CCoeStatic::EThread /*or EApp*/ ) + { + } + +CMySingleton* CMySingleton::SelfL() + { + CMySingleton* self = static_cast<CMySingleton*>( CCoeStatic::Static( KUidMySingleton ) ) ; + if(!self) + { + self = new( ELeave ) CMySingleton() ; + } + return self ; + } + +CMySingleton* CMySingleton::SelfL( CCoeEnv* aCoeEnv ) + { + CMySingleton* self = static_cast<CMySingleton*>( aCoeEnv->FindStatic( KUidMySingleton ) ) ; + if( !self ) + { + self = new( ELeave ) CMySingleton() ; + } + return self ; + } + +

A singleton must be given a UID. When it is instantiated for the first +time the base class constructor adds it to the list of singletons in the environment. +Any subsequent attempts to instantiate the same singleton will result in a +panic.

Singletons may be given a destruction priority and a scope.

The destruction priority determines when the singleton is destroyed +relative to any other singletons in the environment's list and relative to +the App Ui. The default priority, EDefaultDestructionPriority, +is 100. The higher the priority, the earlier the singleton will be destroyed. +A negative value indicates that the singleton should be destroyed after the +AppUi. The more negative the value, the later the destruction.

The scope may be EThread (the default) or EApp and +determines the visibility of the singleton.

Once a singleton has been created it may be accessed through the CCoeEnv API.

+// Singleton access +IMPORT_C static CCoeStatic* Static( TUid aUid ) ; +IMPORT_C CCoeStatic* FindStatic( TUid aUid ) ; + \ No newline at end of file