单例模式在软件开发中经常用到,在iOS系统framework也很多地方用到单例模式,例如 [NSUserDefaults standardUserDefaults], [NSBundle mainBundle]等,下面演示一下iOS如何实现单例模式
MRC模式
SingletonClass.h
#import <Foundation/Foundation.h> @interface SingletonClass : NSObject + (SingletonClass *)sharedInstance; @end
SingletonClass.m
#import "SingletonClass.h" @implementation SingletonClass static SingletonClass *_singletonInstance = nil;
+ (instancetype)sharedInstance{
@synchronized(self){
if (!_singletonInstance) {
_singletonInstance = [[self alloc] init];
}
}
return _singletonInstance;
} + (id)allocWithZone:(NSZone *)zone{
@synchronized(self){
if (!_singletonInstance) {
_singletonInstance = [super allocWithZone:zone];
}
return _singletonInstance;
}
return nil;
} - (instancetype)copyWithZone:(NSZone *)zone;
{
return self;
} - (instancetype)retain
{
return self;
} - (unsigned)retainCount
{
return UINT_MAX;
} - (instancetype)autorelease
{
return self;
} - (oneway void)release
{
} @end
懒人技巧:把单例的定义与实现定义成宏
//单例头宏
#define DEFINE_SINGLETON_HEADER(className) \
+ (className *)sharedInstance; \ //单例实现宏
#define DEFINE_SINGLETON_IMPLEMENTATION(className) \
static className *_singletonInstance = nil; \
+ (instancetype)sharedInstance{ \
@synchronized(self){ \
if (!_singletonInstance) { \
_singletonInstance = [[self alloc] init]; \
} \
} \
return _singletonInstance; \
} \
\
+ (id)allocWithZone:(NSZone *)zone{ \
@synchronized(self){ \
if (!_singletonInstance) { \
_singletonInstance = [super allocWithZone:zone]; \
} \
return _singletonInstance; \
} \
return nil; \
} \
\
- (instancetype)copyWithZone:(NSZone *)zone; \
{ \
return self; \
} \
\
- (instancetype)retain \
{ \
return self; \
} \
\
- (unsigned)retainCount \
{ \
return UINT_MAX; \
} \
\
- (instancetype)autorelease \
{ \
return self; \
} \
\
- (oneway void)release \
{ \
} \
SingletonDefine
#import <Foundation/Foundation.h>
#import "SingletonDefine.h" @interface SingletonClass : NSObject DEFINE_SINGLETON_HEADER(SingletonClass) @end
SingletonClass.h
#import "SingletonClass.h" @implementation SingletonClass DEFINE_SINGLETON_IMPLEMENTATION(SingletonClass) @end
SingletonClass.m
ARC模式
SingletonClass.h
#import <Foundation/Foundation.h> @interface SingletonClass : NSObject + (instancetype)sharedInstance; //禁用alloc,init,new 创建对象,否则编译会报错
+(instancetype) alloc __attribute__((unavailable("alloc not available, call sharedInstance instead")));
-(instancetype) init __attribute__((unavailable("init not available, call sharedInstance instead")));
+(instancetype) new __attribute__((unavailable("new not available, call sharedInstance instead"))); @end
SingletonClass.m
#import "SingletonClass.h" @implementation SingletonClass +(instancetype) sharedInstance {
static dispatch_once_t predicate;
static SingletonClass *instance = nil;
dispatch_once(&predicate, ^{
instance = [[super alloc] initUniqueInstance];
});
return instance;
} -(instancetype) initUniqueInstance {
return [super init];
} - (instancetype)copyWithZone:(NSZone *)zone
{
return self;
} @end
懒人模式
//单例头宏(ARC)
#define DEFINE_SINGLETON_HEADER(className) \
+ (instancetype)sharedInstance; \ //单例实现宏(ARC)
#define DEFINE_SINGLETON_IMPLEMENTATION(className) \
+(instancetype) sharedInstance { \
static dispatch_once_t predicate; \
static className *_singletonInstance = nil; \
dispatch_once(&predicate, ^{ \
_singletonInstance = [[super alloc] init]; \
}); \
return _singletonInstance; \
} \
\
- (instancetype)copyWithZone:(NSZone *)zone \
{ \
return self; \
} \
SingletonDefine.h
#import <Foundation/Foundation.h>
#import "SingletonDefine.h" @interface SingletonClass : NSObject DEFINE_SINGLETON_HEADER(SingletonClass) @end
SingletonClass.h
#import "SingletonClass.h" @implementation SingletonClass DEFINE_SINGLETON_IMPLEMENTATION(SingletonClass) @end
SingletonClass.m