(转)Objective-C的单例模式(singleton)
(转自:http://blog.csdn.net/arthurchenjs/article/details/6699598)
如果你准备写一个类,希望保证只有一个实例存在,同时可以得到这个特定实例提供服务的入口,那么可以使用单态设计模式。
单态模式在Java、C++中很常用,在Cocoa里,也可以实现。
但是,
Objective-C的单例模式绝对和你所想象不一样,他的写法和你所见过的所有语言的写法都不一样。
官方建议
由于自己设计单态模式存在一定风险,主要是考虑到可能在多线程情况下会出现的问题,因此苹果官方建议使用以下方式来实现单态模式:
static MyGizmoClass *sharedGizmoManager = nil;
+ (MyGizmoClass*)sharedManager
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
[[self alloc] init]; // assignment not done here
}
}
return sharedGizmoManager;
}
+ (id)allocWithZone:(NSZone *)zone
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
sharedGizmoManager = [super allocWithZone:zone];
return sharedGizmoManager; // assignment and return on first allocation
}
}
return nil; //on subsequent allocation attempts return nil
}
- (id)copyWithZone:(NSZone *)zone
{
return self;
}
- (id)retain
{
return self;
}
- (unsigned)retainCount
{
return UINT_MAX; //denotes an object that cannot be released
}
- (void)release
{
//do nothing
}
- (id)autorelease
{
return self;
}
开源模板(附下载地址)
程序员都是偷懒的,现在流行使用一个宏定义来搞定这许多的事,而且考虑的更加周全。
单例包含以下接口
+ (MyClass*) sharedInstance;
+ (void) purgeSharedInstance;
调用sharedInstance会创建并返回单例
调用purgeSharedInstance会销毁单例
手动调用alloc也可以保证是单例,你可以这样调用
[[MyClass alloc] initWithParam:firstParam secondParam:secondParam];
只是要保证在sharedInstance之前调用,因为只有一次创建机会。
下面是使用宏的写法“
MyClass.h:
========================================
#import "SynthesizeSingleton.h"
@interface MyClass: SomeSuperclass
{
...
}
SYNTHESIZE_SINGLETON_FOR_CLASS_HEADER(MyClass);
@end
========================================
MyClass.m:
========================================
#import "MyClass.h"
@implementation MyClass
SYNTHESIZE_SINGLETON_FOR_CLASS(MyClass);
...
@end
========================================
下载地址
http://arthurchen.blog.51cto.com/attachment/201108/2483760_1313658868.rar
以上转载完毕。
----------------------------------分割线------------------------------------
以下是本人(xiaou)补充的:
上面下载地址下载下来的开源模板内容如下:(经本人在xcode4环境下验证修改了一两处compiled error)
文件名:SynthesizeSingleton.h
----------------------------------分割线------------------------------------
#ifndef SYNTHESIZE_SINGLETON_FOR_CLASS
#import <objc/runtime.h>
#pragma mark -
#pragma mark Singleton
/* Synthesize Singleton For Class
*
* Creates a singleton interface for the specified class with the following methods:
*
* + (MyClass*) sharedInstance;
* + (void) purgeSharedInstance;
*
* Calling sharedInstance will instantiate the class and swizzle some methods to ensure
* that only a single instance ever exists.
* Calling purgeSharedInstance will destroy the shared instance and return the swizzled
* methods to their former selves.
*
*
* Usage:
*
* MyClass.h:
* ========================================
* #import "SynthesizeSingleton.h"
*
* @interface MyClass: SomeSuperclass
* {
* ...
* }
* SYNTHESIZE_SINGLETON_FOR_CLASS_HEADER(MyClass);
*
* @end
* ========================================
*
*
* MyClass.m:
* ========================================
* #import "MyClass.h"
*
* @implementation MyClass
*
* SYNTHESIZE_SINGLETON_FOR_CLASS(MyClass);
*
* ...
*
* @end
* ========================================
*
*
* Note: Calling alloc manually will also initialize the singleton, so you
* can call a more complex init routine to initialize the singleton like so:
*
* [[MyClass alloc] initWithParam:firstParam secondParam:secondParam];
*
* Just be sure to make such a call BEFORE you call "sharedInstance" in
* your program.
*/
#define SYNTHESIZE_SINGLETON_FOR_CLASS_HEADER(__CLASSNAME__) \
\
+ (__CLASSNAME__*) sharedInstance; \
+ (void) purgeSharedInstance;
#define SYNTHESIZE_SINGLETON_FOR_CLASS(__CLASSNAME__) \
\
static __CLASSNAME__* volatile _##__CLASSNAME__##_sharedInstance = nil; \
\
+ (__CLASSNAME__*) sharedInstanceNoSynch \
{ \
return (__CLASSNAME__*) _##__CLASSNAME__##_sharedInstance; \
} \
\
+ (__CLASSNAME__*) sharedInstanceSynch \
{ \
@synchronized(self) \
{ \
if(nil == _##__CLASSNAME__##_sharedInstance) \
{ \
_##__CLASSNAME__##_sharedInstance = [[self alloc] init]; \
} \
else \
{ \
NSAssert2(1==0, @"SynthesizeSingleton: %@ ERROR: +(%@ *)sharedInstance method did not get swizzled.", self, self); \
} \
} \
return (__CLASSNAME__*) _##__CLASSNAME__##_sharedInstance; \
} \
\
+ (__CLASSNAME__*) sharedInstance \
{ \
return [self sharedInstanceSynch]; \
} \
\
+ (id)allocWithZone:(NSZone*) zone \
{ \
@synchronized(self) \
{ \
if (nil == _##__CLASSNAME__##_sharedInstance) \
{ \
_##__CLASSNAME__##_sharedInstance = [super allocWithZone:zone]; \
if(nil != _##__CLASSNAME__##_sharedInstance) \
{ \
Method newSharedInstanceMethod = class_getClassMethod(self, @selector(sharedInstanceNoSynch)); \
method_setImplementation(class_getClassMethod(self, @selector(sharedInstance)), method_getImplementation(newSharedInstanceMethod)); \
method_setImplementation(class_getInstanceMethod(self, @selector(retainCount)), class_getMethodImplementation(self, @selector(retainCountDoNothing))); \
method_setImplementation(class_getInstanceMethod(self, @selector(release)), class_getMethodImplementation(self, @selector(releaseDoNothing))); \
method_setImplementation(class_getInstanceMethod(self, @selector(autorelease)), class_getMethodImplementation(self, @selector(autoreleaseDoNothing))); \
} \
} \
} \
return _##__CLASSNAME__##_sharedInstance; \
} \
\
+ (void)purgeSharedInstance \
{ \
@synchronized(self) \
{ \
if(nil != _##__CLASSNAME__##_sharedInstance) \
{ \
Method newSharedInstanceMethod = class_getClassMethod(self, @selector(sharedInstanceSynch)); \
method_setImplementation(class_getClassMethod(self, @selector(sharedInstance)), method_getImplementation(newSharedInstanceMethod)); \
method_setImplementation(class_getInstanceMethod(self, @selector(retainCount)), class_getMethodImplementation(self, @selector(retainCountDoSomething))); \
method_setImplementation(class_getInstanceMethod(self, @selector(release)), class_getMethodImplementation(self, @selector(releaseDoSomething))); \
method_setImplementation(class_getInstanceMethod(self, @selector(autorelease)), class_getMethodImplementation(self, @selector(autoreleaseDoSomething))); \
[_##__CLASSNAME__##_sharedInstance release]; \
_##__CLASSNAME__##_sharedInstance = nil; \
} \
} \
} \
\
- (id)copyWithZone:(NSZone *)zone \
{ \
return self; \
} \
\
- (id)retain \
{ \
return self; \
} \
\
- (NSUInteger)retainCount \
{ \
NSAssert1(1==0, @"SynthesizeSingleton: %@ ERROR: -(NSUInteger)retainCount method did not get swizzled.", self); \
return NSUIntegerMax; \
} \
\
- (NSUInteger)retainCountDoNothing \
{ \
return NSUIntegerMax; \
} \
- (NSUInteger)retainCountDoSomething \
{ \
return [super retainCount]; \
} \
\
- (oneway void)release \
{ \
NSAssert1(1==0, @"SynthesizeSingleton: %@ ERROR: -(void)release method did not get swizzled.", self); \
} \
\
- (void)releaseDoNothing{} \
\
- (void)releaseDoSomething \
{ \
@synchronized(self) \
{ \
[super release]; \
} \
} \
\
- (id)autorelease \
{ \
NSAssert1(1==0, @"SynthesizeSingleton: %@ ERROR: -(id)autorelease method did not get swizzled.", self); \
return self; \
} \
\
- (id)autoreleaseDoNothing \
{ \
return self; \
} \
\
- (id)autoreleaseDoSomething \
{ \
return [super autorelease]; \
}
#endif