IOS-单例模式（singleton）

 单例模式

//
//  BWMusicTool.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface BWMusicTool : NSObject<NSCopying>

//@property (nonatomic, strong) NSMutableArray *musics;

+ (instancetype)sharedMusicTool;
@end


//
//  BWMusicTool.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//  懒汉式

#import "BWMusicTool.h"

@interface BWMusicTool ()

@end


@implementation BWMusicTool

static id _instance;


//- (NSArray *)musics
//{
//    if (!_musics) {
//        _musics = [NSMutableArray array];
//        //加载歌曲
//    }
//    return _musics;
//}

//+ (instancetype)alloc
//{
//
//}

//alloc方法内部会调用这个方法
+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
//    NSLog(@"allocWithZone");
    
    if (_instance == nil) {//防止频繁枷锁
        
        @synchronized(self){
            
            if (_instance == nil) {//防止创建多次
                _instance = [super allocWithZone:zone];
            }
        }
    }    return _instance;
}

+ (instancetype)sharedMusicTool
{
    if (_instance == nil) {//防止频繁枷锁
        
        @synchronized(self){
            if (_instance == nil) {//防止创建多次
                
                _instance = [[BWMusicTool alloc] init];
            }
        }
    }
    //return [[self alloc] init];
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}

@end

//
//  BWSoundTool.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface BWSoundTool : NSObject

+ (instancetype)sharedSoundTool;

@end

//
//  BWSoundTool.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//  饿汉式

#import "BWSoundTool.h"

@implementation BWSoundTool

static id _instance;

//当类加载到OC运行时环境中（内存），就会调用一次（一个类只会加载一次）
+ (void)load
{
//    NSLog(@"load1 ----");
    _instance = [[self alloc] init];
//    NSLog(@"load2 ---- %@",_instance);
}

/*
//第一次使用这个类时才会调用
+ (void)initialize
{
   NSLog(@"initialize");
}
*/

//alloc方法内部会调用这个方法
+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
//    NSLog(@"allocWithZone");
    
    if (_instance == nil) {//防止创建多次
        _instance = [super allocWithZone:zone];
    }

    return _instance;
}

+ (instancetype)sharedSoundTool
{
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}


@end

//
//  BWDataModel.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface BWDataModel : NSObject<NSCopying>

+ (instancetype)sharedDataTool;

@end


//
//  BWDataModel.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "BWDataModel.h"

@implementation BWDataModel
//用来保存唯一的单例对象
static id _instance;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
    return _instance;
}
+ (instancetype)sharedDataTool
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [[BWDataModel alloc] init];
    });
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}

@end

//
//  ViewController.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "ViewController.h"
#import "BWMusicTool.h"
#import "BWSoundTool.h"
#import "BWDataModel.h"

@interface ViewController ()

@end

//单例模式可以保证运行过程中，一个类只有一个实例（对象）
@implementation ViewController
/*
 static:修饰变量
 1>修饰全局变量：全局变量的作用域仅限于当前文件内部；
   不用static，在当前文件外部也可以访问（extern id _musicTool;）
 
 2>修饰局部变量：能保证局部变量永远只初始化一次，在运行过程中，永远只有一份
 */
- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor cyanColor];
    
    /***************************懒汉式*********************************/
    BWMusicTool *musicTool1 = [[BWMusicTool alloc] init];
    BWMusicTool *musicTool2 = [BWMusicTool sharedMusicTool];
    // copy 有可能产生新的对象
    BWMusicTool *musicTool3 = [musicTool2 copy];
    NSLog(@"
BWMusicTool:%@ --  %@ -- %@",musicTool1,musicTool2,musicTool3);
    //引用全局变量（并非定义）
//    extern id _musicTool;
//    NSLog(@"%@",_musicTool);
    
    /***************************饿汉式*********************************/
    BWSoundTool *soundTool1 = [[BWSoundTool alloc] init];
    BWSoundTool *soundTool2 = [BWSoundTool sharedSoundTool];
    NSLog(@"
BWSoundTool:%@ --  %@",soundTool1,soundTool2);
    
    /***************************GCD*********************************/
    BWDataModel *dataModel1 = [[BWDataModel alloc] init];
    BWDataModel *dataModel2 = [BWDataModel sharedDataTool];
    NSLog(@"
BWDataModel:%@ --  %@",dataModel1,dataModel2);

}

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

@end

非ARC情况下-保证单例不被释放

//
//  BWDataModel.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "BWSingleton.h"
@interface BWDataModel : NSObject<NSCopying>

+ (instancetype)sharedInstance;
@end


//
//  BWDataModel.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "BWDataModel.h"

@implementation BWDataModel

//用来保存唯一的单例对象
static id _instance;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
    return _instance;
}
+ (instancetype)sharedInstance
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [[BWDataModel alloc] init];
    });
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}

- (oneway void)release
{
    
}

- (instancetype)retain
{
    return  self;
}

- (NSUInteger)retainCount
{
    return 1;
}

- (instancetype)autorelease
{
    return self;
}
 
@end



//
//  ViewController.m
//  IOS_0118_singleton
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "ViewController.h"
#import "BWDataModel.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    BWDataModel *dataModel1 = [[BWDataModel alloc] init];
    BWDataModel *dataModel2 = [BWDataModel sharedInstance];
    NSLog(@"
%@---------%@",dataModel1,dataModel2);
    
}

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

@end

宏定义单例模式

// .h文件
#define BWSingletonH + (instancetype)sharedInstance;

// .m文件
#define BWSingletonM 
 
static id _instance; 
 
+ (instancetype)allocWithZone:(struct _NSZone *)zone 
{ 
    static dispatch_once_t onceToken; 
    dispatch_once(&onceToken, ^{ 
        _instance = [super allocWithZone:zone]; 
    }); 
    return _instance; 
} 
 
+ (instancetype)sharedInstance 
{ 
    static dispatch_once_t onceToken; 
    dispatch_once(&onceToken, ^{ 
        _instance = [[self alloc] init]; 
    }); 
    return _instance; 
} 
 
- (id)copyWithZone:(NSZone *)zone 
{ 
    return _instance; 
} 

//
//  BWDataModel.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "BWSingleton.h"
@interface BWDataModel : NSObject<NSCopying>

BWSingletonH

@end


//
//  BWDataModel.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "BWDataModel.h"

@implementation BWDataModel

BWSingletonM

@end


@end

//
//  ViewController.m
//  IOS_0118_singleton
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "ViewController.h"
#import "BWDataModel.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    BWDataModel *dataModel1 = [[BWDataModel alloc] init];
    BWDataModel *dataModel2 = [BWDataModel sharedInstance];
    NSLog(@"
%@---------%@",dataModel1,dataModel2);
    
}

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

@end

宏定义单例模式(更改方法名及适配MRC和ARC)

BWSingleton.h

// .h文件
#define BWSingletonH(name) + (instancetype)shared##name;


// .m文件
#if __has_feature(objc_arc)

#define BWSingletonM(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;
}

#else

#define BWSingletonM(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;
}

- (oneway void)release
{

}

- (instancetype)retain
{
    return  self;
}

- (NSUInteger)retainCount
{
    return 1;
}

- (instancetype)autorelease
{
    return self;
}

#endif

//
//  BWDataModel.h
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "BWSingleton.h"
@interface BWDataModel : NSObject

BWSingletonH(dataModel)

@end

//
//  BWDataModel.m
//  IOS_0118_hehe
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "BWDataModel.h"

@implementation BWDataModel

BWSingletonM(dataModel)

@end

//
//  ViewController.m
//  IOS_0118_singleton
//
//  Created by ma c on 16/1/18.
//  Copyright (c) 2016年 博文科技. All rights reserved.
//

#import "ViewController.h"
#import "BWDataModel.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    BWDataModel *dataModel1 = [[BWDataModel alloc] init];
    BWDataModel *dataModel2 = [BWDataModel shareddataModel];
    NSLog(@"
%@---------%@",dataModel1,dataModel2);
    
#if __has_feature(objc_arc)
    //编译器环境是ARC
    
#else
    //编译器环境是MRC
    [dataModel2 release];
    [dataModel1 release];
#endif

}

@end