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 */