多线程：GCD 基本使用

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////  ViewController.m//  05-GCD基本使用////  Created by gzxzmac on 16/1/29.//  Copyright © 2016年 gzxzmac. All rights reserved.//#import "ViewController.h"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {    [self gcdDemo3];}/**  跟NSThread 对比 1. GCD使用block ，代码都放在一起，比较直观。NSThread 需要使用selector 来指定线程入口 2. GCD 回到主线程使用 dispatch_get_main_queue .NSThread 回到主线程，只能通过NSObject 的分类方法来实现 */// 同步- (void)gcdDemo {    // 同步    // 任务    void (^task)() = ^ {        NSLog(@"%@",[NSThread currentThread]);    };    dispatch_sync(dispatch_get_global_queue(0, 0), task);}//异步- (void)gcdDemo1 {    void (^task)() = ^ {        NSLog(@"%@",[NSThread currentThread]);    };    dispatch_async(dispatch_get_global_queue(0, 0), task);}// 精简- (void)gcdDemo2 {    dispatch_async(dispatch_get_global_queue(0, 0), ^{        NSLog(@"%@",[NSThread currentThread]);    });}// 线程间通讯- (void)gcdDemo3 {    // 下载    dispatch_async(dispatch_get_global_queue(0, 0), ^{        NSLog(@"正在下载%@",[NSThread currentThread]);        // 回到主线程刷新UI        dispatch_sync(dispatch_get_main_queue(), ^{            NSLog(@"刷新UI%@",[NSThread currentThread]);        });    });}@end
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