GCD使用三 -- 线程间通信

#define HMGlobalQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
#define HMMainQueue dispatch_get_main_queue()

dispatch_async(HMGlobalQueue, ^{
NSLog(@"donwload---%@", [NSThread currentThread]);
// 1.子线程下载图片
NSURL *url = [NSURL URLWithString:@"http://d.hiphotos.baidu.com/image/pic/item/37d3d539b6003af3290eaf5d362ac65c1038b652.jpg"];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *image = [UIImage imageWithData:data];

// 2.回到主线程设置图片
dispatch_async(HMMainQueue, ^{
NSLog(@"setting---%@ %@", [NSThread currentThread], image);
[self.button setImage:image forState:UIControlStateNormal];
});
});

GCD使用三 -- 线程间通信

原文：http://www.cnblogs.com/fangchun/p/4691291.html