线程NSOperationQueue

1.NSOperationQueue下载图片

#import "ViewController.h"
#import "ImageOperation.h"

@interface ViewController ()
{
    NSOperationQueue *_queue;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //图片视图
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(50, 100, 200, 100)];
    [self.view addSubview:imageView];
    
    //创建线程下载
    _queue = [[NSOperationQueue alloc] init];
    ImageOperation *op = [[ImageOperation alloc] init];
    op.urlString = @"http://g.hiphotos.baidu.com/image/pic/item/4034970a304e251fb3145e6ca586c9177e3e5346.jpg";
    op.imageView = imageView;
    
    [_queue addOperation:op];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

2.封装ImageOperation

#import "ImageOperation.h"

@implementation ImageOperation

//线程执行体方法
-(void)main
{
    //下载图片
    NSURL *url = [NSURL URLWithString:self.urlString];
    NSData *data = [NSData dataWithContentsOfURL:url];

　 //在主线程执行方法
    [self performSelectorOnMainThread:@selector(refreshUI:) withObject:data waitUntilDone:YES];
}

-(void)refreshUI:(NSData *)data
{
    self.imageView.image = [UIImage imageWithData:data];
}

@end