单例模式主要实现唯一实例，存活于整个程序范围内，一般存储用户信息经常用到单例，比如用户密码，密码在登录界面用一次，在修改密码界面用一次，而使用单例，就能保证密码唯一实例。如果不用单例模式，init 两个的实例的堆栈地址不一样，所以存放的数据的位置也不一样，当其中一个数据改变，另一个数据依然不变。单例模式的代码如下
.h文件
#ifndef Singleton_h
#define Singleton_h @interface Singleton : NSObject
@property (nonatomic, copy) NSString *pass;
+ (Singleton *) sharedInstance; @end
.m文件
#import <Foundation/Foundation.h>
#import "Singleton.h" @implementation Singleton
static id sharedSingleton = nil;
+ (id)allocWithZone:(struct _NSZone *)zone
{
if (sharedSingleton == nil) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedSingleton = [super allocWithZone:zone];
});
}
return sharedSingleton;
} - (id)init
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedSingleton = [super init];
});
return sharedSingleton;
} + (instancetype)sharedInstance
{
return [[self alloc] init];
}
+ (id)copyWithZone:(struct _NSZone *)zone
{
return sharedSingleton;
}
+ (id)mutableCopyWithZone:(struct _NSZone *)zone
{
return sharedSingleton;
} @end
宏实现单例
#ifndef Singleton_m_h
#define Singleton_m_h // 帮助实现单例设计模式 // .h文件的实现
#define SingletonH(methodName) + (instancetype)shared##methodName; // .m文件的实现
#if __has_feature(objc_arc) // 是ARC
#define SingletonM(methodName) \
static id _instace = nil; \
+ (id)allocWithZone:(struct _NSZone *)zone \
{ \
if (_instace == nil) { \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super allocWithZone:zone]; \
}); \
} \
return _instace; \
} \
\
- (id)init \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super init]; \
}); \
return _instace; \
} \
\
+ (instancetype)shared##methodName \
{ \
return [[self alloc] init]; \
} \
+ (id)copyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
} \
\
+ (id)mutableCopyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
} #else // 不是ARC #define SingletonM(methodName) \
static id _instace = nil; \
+ (id)allocWithZone:(struct _NSZone *)zone \
{ \
if (_instace == nil) { \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super allocWithZone:zone]; \
}); \
} \
return _instace; \
} \
\
- (id)init \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super init]; \
}); \
return _instace; \
} \
\
+ (instancetype)shared##methodName \
{ \
return [[self alloc] init]; \
} \
\
- (oneway void)release \
{ \
\
} \
\
- (id)retain \
{ \
return self; \
} \
\
- (NSUInteger)retainCount \
{ \
return ; \
} \
+ (id)copyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
} \
\
+ (id)mutableCopyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
}
#endif /* Singleton_m_h */