[置顶] GCD的使用

AppDelegate.m

#import "AppDelegate.h"
#import "UIImageView+Download.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];

    //使用GCD完成课堂实例1
//    UIImageView *imgView = [[UIImageView alloc] initWithFrame:self.window.bounds];
//    NSURL *url = [NSURL URLWithString:@"http://h.hiphotos.baidu.com/image/pic/item/10dfa9ec8a136327f5fb6544938fa0ec08fac7b7.jpg"];
//    [imgView loadImgWithUrl:url];
//    
//    [self.window addSubview:imgView];
//    [imgView release];

    //演示GCD延迟调用
    double delayInSeconds = 2.0;
    CFAbsoluteTime first = CFAbsoluteTimeGetCurrent();
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));

    dispatch_after(popTime, dispatch_get_main_queue(), ^{
        NSLog(@"dispatch_after:%lf",CFAbsoluteTimeGetCurrent() - first);
    });

    //dispatch_set_target_queue 使用
    dispatch_queue_t serialQueue = dispatch_queue_create("com.wxhl.serial", NULL);

    dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

    //把serialQueue的优先级设置成跟globalQueue一样
    //第一个参数为需要变更优先级的queue，第二个参数就是参照Queue
    dispatch_set_target_queue(serialQueue, globalQueue);

    dispatch_release(serialQueue);

    return YES;
}



@end

UIImageView + Download.h

@interface UIImageView (Download)

- (void)loadImgWithUrl:(NSURL *)url;

UIImageView + Download.m

- (void)loadImgWithUrl:(NSURL *)url
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *img = [UIImage imageWithData:data];

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


}