IOS 单例模式

 单例模式:
 1.永远只分配一块内存来创建对象
 2.提供一个类方法, 返回内部唯一的一个对象(一个实例)
 3.最好保证init方法也只初始化一次
 

单例模式 ：定义一份变量(整个程序运行过程中, 只有1份)

//static id _instance;

ARC 与非ARC 控制内存内存

// ## : 连接字符串和参数
#define singleton_h(name) + (instancetype)shared##name;

#if __has_feature(objc_arc) // ARC

#define singleton_m(name) 
static id _instance; 
+ (id)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:(struct _NSZone *)zone 
{ 
    return _instance; 
}

#else // 非ARC

#define singleton_m(name) 
static id _instance; 
+ (id)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; 
} 

- (oneway void)release 
{ 

} 

- (id)autorelease 
{ 
return _instance; 
} 

- (id)retain 
{ 
return _instance; 
} 

- (NSUInteger)retainCount 
{ 
return 1; 
} 

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

#endif

调用

#import "HMAudioTool.h"

@interface HMAudioTool()
@end

@implementation HMAudioTool
//// 定义一份变量(整个程序运行过程中, 只有1份)
//static id _instance;

- (id)init
{
    if (self = [super init]) {
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            // 加载资源
            
        });
    }
    return self;
}
singleton_m(AudioTool)

///**
// *  重写这个方法 : 控制内存内存
// */
//+ (id)allocWithZone:(struct _NSZone *)zone
//{
//    // 里面的代码永远只执行1次
//    static dispatch_once_t onceToken;
//    dispatch_once(&onceToken, ^{
//        _instance = [super allocWithZone:zone];
//    });
//    
//    // 返回对象
//    return _instance;
//}
//
//+ (instancetype)sharedAudioTool
//{
//    // 里面的代码永远只执行1次
//    static dispatch_once_t onceToken;
//    dispatch_once(&onceToken, ^{
//        _instance = [[self alloc] init];
//    });
//    
//    // 返回对象
//    return _instance;
//}
//
//+ (id)copyWithZone:(struct _NSZone *)zone
//{
//    return _instance;
//}

调用 HMAudioTool

@interface HMViewController ()

@end

@implementation HMViewController

/**
 单例模式:
 1.永远只分配一块内存来创建对象
 2.提供一个类方法, 返回内部唯一的一个对象(一个实例)
 3.最好保证init方法也只初始化一次
 */

- (void)viewDidLoad
{
    [super viewDidLoad];
    
//    NSObject *obj = [[NSObject alloc] init];
//#if ! __has_feature(objc_arc)
//    [obj release];
//#endif
//    
//    NSObject *obj1 = [[NSObject alloc] init];
//#if ! __has_feature(objc_arc)
//    [obj1 release];
//#endif
//    
//    NSObject *obj2 = [[NSObject alloc] init];
//#if ! __has_feature(objc_arc)
//    [obj2 release];
//#endif
    
    HMAudioTool *tool1 = [HMAudioTool sharedAudioTool];
    HMAudioTool *tool2 = [HMAudioTool sharedAudioTool];
    HMAudioTool *tool3 = [[HMAudioTool alloc] init];
    HMAudioTool *tool4 = [[HMAudioTool alloc] init];
    HMAudioTool *tool5 = [[HMAudioTool alloc] init];
    HMAudioTool *tool6 = [[HMAudioTool alloc] init];

    
//    [tool1 play:@"win.mp3"];
    
    NSLog(@"%p %p %p %p", tool1, tool2, tool3, tool4);
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end