1 前言

使用Dispatch_after ，能夠在你想指定一定數量的延遲之後,使用 GCD 來執行代碼。今天我們就來學習一下。

2 代碼實例
Demo1：

ZYAppDelegate.m

[plain]
- (void) printString:(NSString *)paramString{ 
    NSLog(@"%@", paramString); 
} 
 
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    /* 
     推遲三秒執行printString方法 
     withObject:傳的參數 
     */ 
    [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; 
} 

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

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    /*
     推遲三秒執行printString方法
     withObject:傳的參數
     */
    [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;
}
運行3秒後控制台結果：

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

Demo2：

ZYAppDelegate.m

 

[plain]
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    //設置時間為2 
    double delayInSeconds = 2.0; 
    //創建一個調度時間,相對於默認時鐘或修改現有的調度時間。 
    dispatch_time_t delayInNanoSeconds =dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC); 
    //推遲兩納秒執行 
    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; 
} 

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //設置時間為2
    double delayInSeconds = 2.0;
    //創建一個調度時間,相對於默認時鐘或修改現有的調度時間。
    dispatch_time_t delayInNanoSeconds =dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    //推遲兩納秒執行
    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;
}
運行2秒後控制台結果

 

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

Demo3：

ZYAppDelegate.m

 

[plain]
void processSomething(void *paramContext){ 
    NSLog(@"Processing..."); 
} 
 
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    //設置時間 
    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); 
    //調用C函數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; 
} 

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

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //設置時間
    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);
    //調用C函數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;
}
運行2秒後控制台結果

 

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