IOS第二天多线程-02一次性代码

**********

#import "HMViewController.h"
#import "HMImageDownloader.h"
 
@interface HMViewController ()
//@property (nonatomic, strong) HMImageDownloader *downloader;
@end
 
@implementation HMViewController
 
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
 
//    self.downloader = [[HMImageDownloader alloc] init];
} 
 
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"----touchesBegan");
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{  //只能执行一次
        NSLog(@"----once");
        HMImageDownloader *downloader = [[HMImageDownloader alloc] init];
        [downloader download];
    });
}
 
@end