單例模式

有時(shí)候我們需要一個(gè)全局的對(duì)象葬荷，而且要保證全局有且僅有一份即可,這時(shí)候就需要用到單例設(shè)計(jì)模式,但是需要注意的是：在多線程的環(huán)境下也需要做好線程保護(hù)。其實(shí)系統(tǒng)已經(jīng)有很多單例存在，例如UIApplication娜膘、NSNotification痕届、NSFileManager、NSUserDefaults等.以下代碼詳解

ARC環(huán)境下嚴(yán)謹(jǐn)?shù)膯卫Ｊ?/h4>

#import <Foundation/Foundation.h>
@interface JHTool : NSObject<NSCopying,NSMutableCopying>
//類方法
//1.方便訪問(wèn)
//2.標(biāo)明身份
//3.注意:share+類名|default + 類名 | share | default | 類名
+(instancetype)shareTool;
@end

#import "JHTool.h"
@implementation JHTool
//提供一個(gè)全局靜態(tài)變量
static JHTool * _instance;

+(instancetype)shareTool{
    return [[self alloc]init];
}

//當(dāng)調(diào)用alloc的時(shí)候會(huì)調(diào)用allocWithZone
+(instancetype)allocWithZone:(struct _NSZone *)zone{
    //方案一:加互斥鎖,解決多線程訪問(wèn)安全問(wèn)題
//    @synchronized(self){//同步的
//        if (!_instance) {
//            _instance = [super allocWithZone:zone];
//        }
//    }
    //方案二.GCD dispatch_onec,本身是線程安全的,保證整個(gè)程序中只會(huì)執(zhí)行一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
    return _instance;
}
//嚴(yán)謹(jǐn)
//遵從NSCopying協(xié)議,可以通過(guò)copy方式創(chuàng)建對(duì)象
- (nonnull id)copyWithZone:(nullable NSZone *)zone {
    return _instance;
}
//遵從NSMutableCopying協(xié)議,可以通過(guò)mutableCopy方式創(chuàng)建對(duì)象
- (nonnull id)mutableCopyWithZone:(nullable NSZone *)zone {
    return _instance;
}
@end

#import "ViewController.h"
#import "JHTool.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor redColor];
    JHTool * tool1 = [[JHTool alloc]init];
    JHTool * tool2 = [JHTool shareTool];
    JHTool * tool3 = tool1.copy;
    JHTool * tool4 = tool2.mutableCopy;
    NSLog(@"tool1:%p,tool2:%p,tool3:%p,tool4:%p,",tool1,tool2,tool3,tool4);
    printf("tool1:%p,tool2:%p,tool3:%p,tool4:%p,",tool1,tool2,tool3,tool4);
    
}
@end

打印結(jié)果:

ARC單例模式

MRC環(huán)境下嚴(yán)謹(jǐn)?shù)膯卫Ｊ?/h4>

Xcode5以后項(xiàng)目默認(rèn)都是ARC,所以把項(xiàng)目設(shè)置成MRC環(huán)境,選擇項(xiàng)目 Target -> Build Sttings -> All -> 搜索‘Automatic’ -> 把 Objective-C Automatic Reference Counting 設(shè)置為 NO 徘公，如下圖：

項(xiàng)目設(shè)置成MRC環(huán)境

MRC單例模式代碼詳解

#import <Foundation/Foundation.h>
@interface HJTool : NSObject<NSCopying,NSMutableCopying>
//類方法
+(instancetype)shareTool;
@end

#import "HJTool.h"

@implementation HJTool
//修改環(huán)境為MRC:選擇項(xiàng)目 Target -> Build Sttings -> All -> 搜索‘Automatic’ -> 把 Objective-C Automatic Reference Counting 設(shè)置為 NO
//提供一個(gè)靜態(tài)全局變量
static HJTool * _instance;
//實(shí)現(xiàn)類方法
+(instancetype)shareTool{
    return [[self alloc]init];
}
//alloc會(huì)調(diào)用allocWithZone
+(instancetype)allocWithZone:(struct _NSZone *)zone{
    //方法一.互斥鎖保證線程安全
//    @synchronized(self){
//        if (_instance == nil) {
//            _instance = [super allocWithZone:zone];
//        }
//    }
    //方法一.GCD-> dispatch_once_t 該方法只會(huì)執(zhí)行一次,本身線程安全
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
    return _instance;
}
-(id)copyWithZone:(NSZone *)zone{
    return _instance;
}
-(id)mutableCopyWithZone:(NSZone *)zone{
    return _instance;
}
//MRC特有的
-(instancetype)retain{
    return _instance;
}
-(oneway void)release{
    NSLog(@"%zd",_instance.retainCount);
}

#import "ViewController.h"
#import "HJTool.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor yellowColor];
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    HJTool * t1 = [[HJTool alloc]init];
    HJTool * t2 = [[HJTool alloc]init];
    HJTool * t3 = [HJTool shareTool];
    HJTool * t4 = [t1 copy];
    HJTool * t5 = [t2 mutableCopy];
    HJTool * t6 = [t1 retain];
    NSLog(@"t6.retainCount : %zd",t1.retainCount);
    NSLog(@"t1:%p t2:%p t3:%p t4:%p t5:%p t6:%p",t1,t2,t3,t4,t5,t6);
}

打印結(jié)果

MRC單例模式

拓展:區(qū)分是MRC還是ARC的宏

#if __has_feature(objc_arc)
    //條件滿足 ARC,可以處理ARC的代碼
    NSLog(@"ARC");
#else
    //條件滿足 MRC,,可以處理MRC的代碼
    NSLog(@"MRC");
#endif

通用的單例模式

在SingleDog.h文件中定義一個(gè)宏, SingleH(name)定義單例.h文件的類方法聲明,SingleM(name)定義和實(shí)現(xiàn)單例.m文件的方法,定義的宏的代碼如下

#define SingleH(name) +(instancetype)share##name;//.h文件替換
//.m文件替換
#if __has_feature(objc_arc)//arc
//條件滿足 ARC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}

#else
//條件滿足 MRC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
-(oneway void)release\
{\
}\
\
-(instancetype)retain\
{\
return _instance;\
}
#endif

單例SingleTool文件,頭文件和實(shí)現(xiàn)文件分別調(diào)用宏的SingleH(name),SingleM(name)即可,代碼如下

#import <Foundation/Foundation.h>
#import "SingleDog.h"

@interface SingleTool : NSObject
//替換頭文件
SingleH(SingleTool)

@end

#import "SingleTool.h"

@implementation SingleTool
SingleM(SingleTool)
@end

#import "ViewController.h"
#import "SingleTool.h"

@interface ViewController ()

@end

@implementation ViewController

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    SingleTool * t1 = [[SingleTool alloc]init];
    SingleTool * t2 = [SingleTool shareSingleTool];
    SingleTool * t3 = [t1 copy];
    SingleTool * t4 = [t1 mutableCopy];
#if __has_feature(objc_arc)
    //條件滿足 ARC,可以處理ARC的代碼
    NSLog(@"ARC");
#else
    //條件滿足 MRC,,可以處理MRC的代碼
    NSLog(@"MRC");
    SingleTool * t5 = [t1 retain];
    NSLog(@"t6.retainCount : %zd",t1.retainCount);
    NSLog(@"t1:%p t2:%p t3:%p t4:%p t5:%p",t1,t2,t3,t4,t5);
#endif
}

@end

MRC環(huán)境下打印結(jié)果如下:

MRC通用單例模式