自定义单例

#import <Foundation/Foundation.h>

@interface Person : NSObject


// 获取单例
+ (instancetype)sharePerson;

@end

#import "Person.h"

@implementation Person
// 程序启动时候创建对象

// 静态变量
static Person *_instance = nil;

// 作用:加载类
// 什么调用:每次程序一启动,就会把所有的类加载进内存
+ (void)load
{
    NSLog(@"%s",__func__);
    
   _instance = [[self alloc] init];
    
}

+ (instancetype)sharePerson
{
    return _instance;
}

+ (instancetype)alloc
{
    
    if (_instance) {
        // 标示已经分配好了,就不允许外界在分配内存
        
        // 抛异常,告诉外界不运用分配
        // 'NSInternalInconsistencyException', reason: 'There can only be one UIApplication instance.'

        // 创建异常类
        // name:异常的名称
        // reson:异常的原因
        // userInfo:异常的信息
        NSException *excp = [NSException exceptionWithName:@"NSInternalInconsistencyException" reason:@"There can only be one Person instance." userInfo:nil];
        
        // 抛异常
        [excp raise];
        
    }
    
    
    // super -> NSObject 才知道怎么分配内存
    // 调用系统默认的做法, 当重写一个方法的时候,如果不想要覆盖原来的实现,就调用super
    return [super alloc];
}

@end

 

ARC下,另一种单例的自定义方法:

#import "Tools.h"

@implementation Tools

static Tools *_instance;

//保证只分配一次存储空间
+(instancetype)allocWithZone:(struct _NSZone *)zone
{
//    @synchronized(self) {
//        if (_instance == nil) {
//            _instance = [super allocWithZone:zone];
//        }
//    }
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
   
    return _instance;
}

//返回一个实例化对象,供外界访问
+(instancetype)shareTools
{
    //注意:最好是写self
    
    return [[self alloc]init];
}

//严谨起见
-(id)copyWithZone:(NSZone *)zone
{
//    return [[self class]allocWithZone:zone];
    return _instance;
}

-(id)mutableCopyWithZone:(NSZone *)zone
{
    return _instance;
}
@end

 

MRC下,自定义单例的方法:

#define singleM static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
return _instance;\
}\
\
+(instancetype)shareTools\
{\
return [[self alloc]init];\
}\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
-(oneway void)release\
{\
}\
\
-(instancetype)retain\
{\
    return _instance;\
}\
\
-(NSUInteger)retainCount\
{\
    return MAXFLOAT;\
}