iPhone sdk：倒數計時器

Question

請幫忙。我想用iphone sdk創建倒數計時器。我有當前時間：

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

和時間（s）從數據庫中。例如：currentTime是19:18:30，來自數據庫的時間是19:20:01。所以定時器應該設置爲0:01:31並開始倒計時。到達0:00:00時，再從數據庫中取出一些時間（例如19:21:00），重新設置計時器（0:00:59）和星形倒計時。當到達0:00:00時，採取...定時器應該由UILabel顯示。

請幫忙。它開始讓我發瘋。 :)

Answer 1

試試這個。我只寫了解決方案所需的方法。不要忘記實現的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