iOS开发笔记－两种单例模式的写法

#import "ServiceManager.h"

static ServiceManager *defaultManager;

@implementation ServiceManager

+(ServiceManager *)defaultManager{
    if(!defaultManager)
        defaultManager=[[self allocWithZone:NULL] init];
    return  defaultManager;
}

@end

#import "ServiceManager.h"


@implementation ServiceManager


+(ServiceManager *)sharedManager{
    static dispatch_once_t predicate;
    static ServiceManager * sharedManager;
    dispatch_once(&predicate, ^{
        sharedManager=[[ServiceManager alloc] init];
    });
    return sharedManager;
}

@end