iOS 单例的标准写法

.h

#import <Foundation/Foundation.h>

@interface Singleton : NSObject

+ (instancetype)shareInstance;

@end

.m

#import "Singleton.h"

static Singleton *_instance = nil;

@implementation Singleton

+ (instancetype)shareInstance{
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [[super allocWithZone:NULL]init];
    });
    return _instance;
}

+(id)allocWithZone:(struct _NSZone *)zone
{
    return [Singleton shareInstance] ;
}

-(id)copyWithZone:(struct _NSZone *)zone
{
    return [Singleton shareInstance];
}

@end