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

[plain]
- (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; 
} 

- (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

 

[plain]
- (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; 
} 

- (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

 

[plain]
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; 
} 

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...