iOS 单例模式简单实例

 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 1; 
} 
+ (id)copyWithZone:(struct _NSZone *)zone 
{ 
return _instace; 
} 

+ (id)mutableCopyWithZone:(struct _NSZone *)zone 
{ 
return _instace; 
}
#endif /* Singleton_m_h */