单利模式
单例模式的作用
- 可以保证在程序运行过程，一个类只有一个实例，而且该实例易于供外界访问从而方便地控制了实例个数，并节约系统资源
单例模式的使用场合
-在整个应用程序中，共享一份资源（这份资源只需要创建初始化1次）
ARC中，单例模式的实现
在.m中保留一个全局的static的实例
static id _instance;
重写allocWithZone:方法，在这里创建唯一的实例（注意线程安全）
- (instancetype)allocWithZone:(struct _NSZone *)zone
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [super allocWithZone:zone];
});
return _instance;
}
提供1个类方法让外界访问唯一的实例
- (instancetype)sharedInstance
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[self alloc] init];
});
return _instance;
}
实现copyWithZone:方法
- (id)copyWithZone:(struct _NSZone *)zone
{
return _instance;
}
#import <Foundation/Foundation.h>
@interface XMGPerson : NSObject
/** 名字 */
@property (nonatomic, strong) NSString *name;
+ (instancetype)sharedPerson;
@end
#import "XMGPerson.h"
@interface XMGPerson() <NSCopying>
@end
@implementation XMGPerson
static XMGPerson *_person;
//因为alloc内部会调用allocWithZone
+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_person = [super allocWithZone:zone];
});
return _person;
}
+ (instancetype)sharedPerson
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_person = [[self alloc] init];
});
return _person;
}
- (id)copyWithZone:(NSZone *)zone
{
return _person;
}
@end
单利模式提示宏
// .h文件
#define XMGSingletonH(name) + (instancetype)shared##name;
// .m文件
#define XMGSingletonM(name) \
static id _instance; \
\
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super allocWithZone:zone]; \
}); \
return _instance; \
} \
\
+ (instancetype)shared##name \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[self alloc] init]; \
}); \
return _instance; \
} \
\
- (id)copyWithZone:(NSZone *)zone \
{ \
return _instance; \
}
单利模式宏的使用
#import <Foundation/Foundation.h>
#import "XMGSingleton.h"
@interface XMGPerson : NSObject
/** 名字 */
@property (nonatomic, strong) NSString *name;
XMGSingletonH(Person)
@end
#import "XMGPerson.h"
@interface XMGPerson()
@end
@implementation XMGPerson
XMGSingletonM(Person)
@end
#import "ViewController.h"
#import "XMGPerson.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[XMGPerson sharedPerson];
}
@end
非GCD实现单利模式
#import <Foundation/Foundation.h>
@interface XMGPerson : NSObject
+ (instancetype)sharedInstance;
@end
#import "XMGPerson.h"
@interface XMGPerson()
@end
@implementation XMGPerson
static id _instance;
+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
@synchronized(self) {
if (_instance == nil) {
_instance = [super allocWithZone:zone];
}
}
return _instance;
}
+ (instancetype)sharedInstance
{
@synchronized(self) {
if (_instance == nil) {
_instance = [[self alloc] init];
}
}
return _instance;
}
- (id)copyWithZone:(NSZone *)zone
{
return _instance;
}
@end
