NSOperationQueue 多线程

staticNSOperationQueue * queue;

- (void)viewDidLoad

{

 　　[superviewDidLoad];

 　　queue = [[NSOperationQueuealloc] init];

    　NSInvocationOperation * op = [[NSInvocationOperationalloc] initWithTarget:selfselector:@selector(download) object:nil];

   　[queueaddOperation:op];

 

}

- (void)download {

    NSURL * url = [NSURLURLWithString:@"http://www.youdao.com"];

    NSError * error;

    NSString * data = [NSStringstringWithContentsOfURL:url encoding:NSUTF8StringEncodingerror:&error];

    if (data != nil) {

        [selfperformSelectorOnMainThread:@selector(download_completed:) withObject:data waitUntilDone:NO];

    } else {

        NSLog(@"error when download:%@", error);

        queue = nil;

    }

}

- (void) download_completed:(NSString *) data {

    NSLog(@"call back");

 

    self->contentLabel.text = data;

    queue = nil;

}