iPhone sdk：倒数计时器

Question

请帮忙。我想用iphone sdk创建倒数计时器。我有当前时间：

NSDate *today = [NSDate date]; 
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; 
[dateFormatter setDateFormat:@"HH:mm"]; 
NSString *currentTime = [dateFormatter stringFromDate:today]; 
[dateFormatter release]; 

和时间（s）从数据库中。例如：currentTime是19:18:30，来自数据库的时间是19:20:01。所以定时器应该设置为0:01:31并开始倒计时。到达0:00:00时，再从数据库中取出一些时间（例如19:21:00），重新设置计时器（0:00:59）和星形倒计时。当到达0:00:00时，采取...定时器应该由UILabel显示。

请帮忙。它开始让我发疯。 :)

Answer 1

试试这个。我只写了解决方案所需的方法。不要忘记实现的dealloc等

CountdownViewController.h

@interface CountdownViewController : UIViewController {  
     IBOutlet UILabel *clockLabel; 
     NSDate *databaseDate; 
     NSTimer *timer; 
    } 

    @property(nonatomic, retain) IBOutlet UILabel *clockLabel; 
    @property(nonatomic, retain) NSDate *databaseDate; 

    @end 

CountdownViewController.m

@implementation CountdownViewController 

@synthesize clockLabel; 
@synthesize databaseDate; 

- (void) showClock { 
    NSTimeInterval remainingSec = [databaseDate timeIntervalSinceNow]; 
    if (!timer || remainingSec <= 0) { 
     [timer invalidate]; 
     timer = nil; 
     // getting time from database 
     self.databaseDate = [NSDate dateWithTimeIntervalSinceNow:20.0]; 
     remainingSec = [databaseDate timeIntervalSinceNow]; 
     timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self 
               selector:@selector(showClock) 
               userInfo:nil 
               repeats:YES]; 
    } 

    NSInteger hours = remainingSec/3600; 
    NSInteger remainder = ((NSInteger)remainingSec)% 3600; 
    NSInteger minutes = remainder/60; 
    NSInteger seconds = remainder % 60; 

    clockLabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds]; 
} 

@end