iOS多线程---GCD中线程的通信

   [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];

  dispatch_async(dispatch_get_main_queue(), ^{             
          self.imageView.image=image;          
  });

//
//  ViewController.m
//  GCDTest
//
//  Created by 登 on 2017/6/16.
//  Copyright ? 2017年 登. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"主线程----%@",[NSThread mainThread]);

}

-(void)touchesBegan:(NSSet*)touches withEvent:(UIEvent *)event
{
    //1 获取一个全局队列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 2 把任务添加到队列中执行
    dispatch_async(queue, ^{
        
        //打印当前的线程
        NSLog(@"%@",[NSThread currentThread]);
        
        //3.从网络下载图片
        NSURL *urlStr = [NSURL URLWithString:@"http://h.hiphotos.baidu.com/baike/w%3D268/sign=30b3fb747b310a55c424d9f28f444387/1e30e924b899a9018b8d3ab11f950a7b0308f5f9.jpg"];
        NSData *data = [NSData dataWithContentsOfURL:urlStr];
        UIImage *image = [UIImage imageWithData:data];
        
        //提示
        NSLog(@"图片加载完毕");
        
        //4.回到主线程，展示图片
       // [self.imageView performSelectorOnMainThread:@selector(setImageView:) withObject:image waitUntilDone:NO];
        dispatch_async(dispatch_get_main_queue(), ^{
            _imageView.image = image;
            
            NSLog(@"%@",[NSThread currentThread]);
        });
    });
    
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

@end