1.单例模式（Singleton）基本概念
- 什么是单例模式
- 单例模式即一个类的对象为唯一的一个实例对象，内存地址相同
2.单例模式的简单实现
- 自定义
QLPlayer类，使其成为单例- 遵守苹果的规范，单例一般会提供
sharedXXX或者defaultXXX方法 - 为实现
copy和mutableCopy方法，遵守NSCopying和NSMutableCopying协议
- 遵守苹果的规范，单例一般会提供
#import <Foundation/Foundation.h>
@interface QLPlayer : NSObject <NSCopying, NSMutableCopying>
+ (instancetype)sharedPlayer;
@end
- 类的实现
- 因为alloc方法内部会调用
allocWithZone，故重写allocWithZone方法实现单例 - 调用
dispatch_once函数，保证了在多线程同时调用的情况下，依然返回单例对象
#import "QLPlayer.h"
@implementation QLPlayer
+ (instancetype)sharedPlayer
{
QLPlayer *instance = [[self alloc] init];
return instance;
}
static QLPlayer *_instance = nil;
+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[super allocWithZone:zone] init];
});
return _instance;
}
- (id)copyWithZone:(NSZone *)zone
{
return _instance;
}
- (id)mutableCopyWithZone:(NSZone *)zone
{
return _instance;
}
验证
- 用五种不同的方法创建
QLPlayer对象，打印对象内存地址
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
QLPlayer *player1 = [QLPlayer sharedPlayer];
QLPlayer *player2 = [[QLPlayer alloc] init];
QLPlayer *player3 = [QLPlayer new];
QLPlayer *player4 = [player1 copy];
QLPlayer *player5 = [player1 mutableCopy];
NSLog(@"%p, %p, %p, %p, %p", player1, player2, player3, player4, player5);
}
@end
-
结果如下，内存地址相同，说明是单例对象！
3.单例模式宏抽取
- 用
interfaceSingleton(Name)来代替自定义单例对象类方法的声明
#define interfaceSingleton(Name) +(instancetype)shared##Name
- 用
implementationSingleton(Name)来代替自定义单例对象类方法的实现
#define implementationSingleton(Name) \
+ (instancetype)shared##Name \
{ \
Name *instance = [[self alloc] init]; \
return instance; \
} \
static Name *_instance = nil; \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[super allocWithZone:zone] init]; \
}); \
return _instance; \
} \
- (id)copyWithZone:(NSZone *)zone \
{ \
return _instance; \
} \
- (id)mutableCopyWithZone:(NSZone *)zone \
{ \
return _instance; \
}
注意：如果是在MRC中，还需实现以下方法：
- (instancetype)retain
{
return _player;
}
- (oneway void)release
{
//为了保证只有一个实例对象，这里do nothing
}
- (NSUInteger)retainCount
{
return MAXFLOAT; //表示这是个单例对象
}
相应的，抽取的宏中，方法的声明部分不许改变，方法的实现部分，需改为：
#if __has_feature(objc_arc)
// 说明是ARC模式
#define implementationSingleton(Name) \
+ (instancetype)shared##Name \
{ \
Name *instance = [[self alloc] init]; \
return instance; \
} \
static Name *_instance = nil; \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[super allocWithZone:zone] init]; \
}); \
return _instance; \
} \
- (id)copyWithZone:(NSZone *)zone \
{ \
return _instance; \
} \
- (id)mutableCopyWithZone:(NSZone *)zone \
{ \
return _instance; \
}
#else
// 说明是MRC模式
#define implementationSingleton(Name) \
+ (instancetype)shared##Name \
{ \
Name *instance = [[self alloc] init]; \
return instance; \
} \
static Name *_instance = nil; \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[super allocWithZone:zone] init]; \
}); \
return _instance; \
} \
- (id)copyWithZone:(NSZone *)zone \
{ \
return _instance; \
} \
- (id)mutableCopyWithZone:(NSZone *)zone \
{ \
return _instance; \
} \
- (instancetype)retain \
{ \
return _player; \
} \
- (oneway void)release \
{ \
} \
- (NSUInteger)retainCount \
{ \
return MAXFLOAT; \
}
#endif
验证
- 自定义
QLCar类，.h、.m文件如下
#import <Foundation/Foundation.h>
#import "QLSingleton.h"
@interface QLCar : NSObject
interfaceSingleton(QLCar);
@end
#import "QLCar.h"
@implementation QLCar
implementationSingleton(QLCar)
@end
- 用五种不同的方法创建
QLCar对象，打印对象内存地址
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
QLCar *car1 = [QLCar sharedQLCar];
QLCar *car2 = [[QLCar alloc] init];
QLCar *car3 = [QLCar new];
QLCar *car4 = [car1 copy];
QLCar *car5 = [car1 mutableCopy];
NSLog(@"%p, %p, %p, %p, %p", car1, car2, car3, car4, car5);
}
@end
-
结果如下，内存地址相同，说明是单例对象！
