1 // 2 // ViewController.m 3 // 06一次性代码-GCD 4 // 5 // Created by mac on 16/4/21. 6 // Copyright © 2016年 mac. All rights reserved. 7 // 8 9 #import "ViewController.h" 10 11 @interface ViewController () 12 13 @property (assign, nonatomic) BOOL isHave; 14 15 16 @end 17 18 @implementation ViewController 19 20 - (void)viewDidLoad { 21 [super viewDidLoad]; 22 23 } 24 25 /** 26 * 1. flag保证只打印一次 27 */ 28 - (void)download { 29 30 if (self.isHave) return; 31 32 NSLog(@"ishave"); 33 self.isHave = YES; 34 35 } 36 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event { 37 38 [self downLoadDispatch]; 39 } 40 41 /** 42 * 2. dispatch_once_t保证只打印一次 43 */ 44 - (void)downLoadDispatch { 45 46 static dispatch_once_t onceToken; 47 dispatch_once(&onceToken, ^{ 48 49 NSLog(@"downLoadDispatch"); 50 }); 51 } 52 53 @end