1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // Support for using the Singleton<T> pattern with Objective-C objects. A 6 // SingletonObjC is the same as a Singleton, except the default traits are 7 // appropriate for Objective-C objects. A typical Objective-C object of type 8 // NSExampleType can be maintained as a singleton and accessed with: 9 // 10 // NSExampleType* exampleSingleton = SingletonObjC<NSExampleType>::get(); 11 // 12 // The first time this is used, it will create exampleSingleton as the result 13 // of [[NSExampleType alloc] init]. Subsequent calls will return the same 14 // NSExampleType* object. The object will be released by calling 15 // -[NSExampleType release] when Singleton's atexit routines run 16 // (see singleton.h). 17 // 18 // For Objective-C objects initialized through means other than the 19 // no-parameter -init selector, DefaultSingletonObjCTraits may be extended 20 // as needed: 21 // 22 // struct FooSingletonTraits : public DefaultSingletonObjCTraits<Foo> { 23 // static Foo* New() { 24 // return [[Foo alloc] initWithName:@"selecty"]; 25 // } 26 // }; 27 // ... 28 // Foo* widgetSingleton = SingletonObjC<Foo, FooSingletonTraits>::get(); 29 30 #ifndef BASE_MEMORY_SINGLETON_OBJC_H_ 31 #define BASE_MEMORY_SINGLETON_OBJC_H_ 32 #pragma once 33 34 #import <Foundation/Foundation.h> 35 #include "base/memory/singleton.h" 36 37 // Singleton traits usable to manage traditional Objective-C objects, which 38 // are instantiated by sending |alloc| and |init| messages, and are deallocated 39 // in a memory-managed environment when their retain counts drop to 0 by 40 // sending |release| messages. 41 template<typename Type> 42 struct DefaultSingletonObjCTraits : public DefaultSingletonTraits<Type> { NewDefaultSingletonObjCTraits43 static Type* New() { 44 return [[Type alloc] init]; 45 } 46 DeleteDefaultSingletonObjCTraits47 static void Delete(Type* object) { 48 [object release]; 49 } 50 }; 51 52 // Exactly like Singleton, but without the DefaultSingletonObjCTraits as the 53 // default trait class. This makes it straightforward for Objective-C++ code 54 // to hold Objective-C objects as singletons. 55 template<typename Type, 56 typename Traits = DefaultSingletonObjCTraits<Type>, 57 typename DifferentiatingType = Type> 58 class SingletonObjC : public Singleton<Type, Traits, DifferentiatingType> { 59 }; 60 61 #endif // BASE_MEMORY_SINGLETON_OBJC_H_ 62