单例模式的设计

#import "NetworkTools.h"

//GCD方式实现单例

@implementation NetworkTools

+ (instancetype)shareTools{

static id instance;

static dispatch_once_t onceToken;

dispatch_once (&onceToken),^{

//这个方法只会执行一次

instance = [[NetworkTools alloc] init];

})

return instance;

}

//同步锁方式实现单例

+(instancetype)shareTools{

static id instance;

@synchronized(self){

if (instance== nil){

instancetype = [NetworkTools alloc] init];

  }

}

return instance;

}