IOS开发（63）之GCD执行延迟操作

1 前言

使用Dispatch_after ，能够在你想指定一定数量的延迟之后,使用 GCD 来执行代码。今天我们就来学习一下。

2 代码实例

Demo1：

ZYAppDelegate.m

- (void) printString:(NSString *)paramString{
    NSLog(@"%@", paramString);
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    /*
     推迟三秒执行printString方法
     withObject:传的参数
     */
    [self performSelector:@selector(printString:) withObject:@"Grand Central Dispatch" afterDelay:3.0];
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.viewController = [[[ZYViewController alloc] initWithNibName:@"ZYViewController" bundle:nil] autorelease];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

运行3秒后控制台结果：

2013-05-10 17:04:52.710 GCDAfterTest[2385:c07] Grand Central Dispatch

Demo2：

ZYAppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //设置时间为2
    double delayInSeconds = 2.0;
    //创建一个调度时间,相对于默认时钟或修改现有的调度时间。
    dispatch_time_t delayInNanoSeconds =dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    //推迟两纳秒执行
    dispatch_queue_t concurrentQueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_after(delayInNanoSeconds, concurrentQueue, ^(void){
        NSLog(@"Grand Center Dispatch!");
    });
    
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.viewController = [[[ZYViewController alloc] initWithNibName:@"ZYViewController" bundle:nil] autorelease];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

运行2秒后控制台结果

2013-05-10 17:06:27.023 GCDAfterTest2[2435:1303] Grand Center Dispatch!

Demo3：

ZYAppDelegate.m

void processSomething(void *paramContext){
    NSLog(@"Processing...");
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //设置时间
    double delayInSeconds = 2.0;
    dispatch_time_t delayInNanoSeconds =
    dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //调用C函数processSomething
    dispatch_after_f(delayInNanoSeconds, concurrentQueue,
                     NULL,
                     processSomething);
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.viewController = [[[ZYViewController alloc] initWithNibName:@"ZYViewController" bundle:nil] autorelease];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

运行2秒后控制台结果

2013-05-10 17:07:27.660 GCDAfterTest3[2476:1303] Processing...

3 结语

以上是所有内容，希望对大家有所帮助。

Demo代码下载：http://download.csdn.net/detail/u010013695/5353603