倒计时计时器 - iPhone

Question

我想显示倒计时计时器。我有开始日期和结束日期。我需要显示剩余时间，如下：

天：小时：分钟：秒

我该怎么做？

- Dev

---

https://dev59.com/N1LTa4cB1Zd3GeqPcJ4H - Ramaraj T

我的代码已经实现了，它运行得很好。我只是添加了输出，请检查一下。 - Nitin Gohel

Answer 1

你可以像下面的代码一样设置倒计时：

 -(void) viewWillAppear:(BOOL)animated
 {
 timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(updateCountdown) userInfo:nil repeats: YES];
 }

与

 -(void) updateCountdown 
 {

NSString *dateString = @"14-12-2012";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setDateFormat:@"dd-MM-yyyy"];
NSDate *dateFromString = [[NSDate alloc] init];
// voila!
dateFromString = [dateFormatter dateFromString:dateString];


NSDate *now = [NSDate date];
NSCalendar *calendar = [NSCalendar currentCalendar];



NSDateComponents *componentsHours = [calendar components:NSHourCalendarUnit fromDate:now];
NSDateComponents *componentMint = [calendar components:NSMinuteCalendarUnit fromDate:now];    
NSDateComponents *componentSec = [calendar components:NSSecondCalendarUnit fromDate:now];        


NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *componentsDaysDiff = [gregorianCalendar components:NSDayCalendarUnit
                                                            fromDate:now
                                                              toDate:dateFromString
                                                             options:0];



lblDaysSetting.text=[NSString stringWithFormat:@"%02d",componentsDaysDiff.day];
lblHouresSetting.text=[NSString stringWithFormat:@"%02d",(24-componentsHours.hour)];    
lblMinitSetting.text=[NSString stringWithFormat:@"%02d",(60-componentMint.minute)];  
lblSecSetting.text=[NSString stringWithFormat:@"%02d",(60-componentSec.second)];  



 }

现在只需设置您的逻辑

它的代码输出如下所示：

- Nitin Gohel

---

从后台返回后，它能正常工作吗？ - Dev

当我最小化我的应用程序时，倒计时时钟会停止还是继续在后台运行？ - Dev

是的，当你重新打开应用时，它会运行并调用ViewwillApear方法，因此它将以当前时间运行，而不是从头开始。但是，如果你设置了静态的启动时间，它将从该时间开始运行。 - Nitin Gohel

Answer 2

以下是.h文件的代码：

@interface UIMyContoller : UIViewController {

NSTimer *timer;
IBOutlet UILabel *myCounterLabel;
}

@property (nonatomic, retain) UILabel *myCounterLabel;
-(void)updateCounter:(NSTimer *)theTimer;
-(void)countdownTimer;

@end

以下是 .m 文件的代码：

@implementation UIMyController
@synthesize myCounterLabel;

int hours, minutes, seconds;
int secondsLeft;

- (void)viewDidLoad {
[super viewDidLoad];

secondsLeft = 16925;
[self countdownTimer];
}

- (void)updateCounter:(NSTimer *)theTimer {
if(secondsLeft > 0 ){
    secondsLeft -- ;
    hours = secondsLeft / 3600;
    minutes = (secondsLeft % 3600) / 60;
    seconds = (secondsLeft %3600) % 60;
    myCounterLabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
}
else{
    secondsLeft = 16925;
}
}

-(void)countdownTimer{

secondsLeft = hours = minutes = seconds = 0;
if([timer isValid])
{
    [timer release];
}
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];  
timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES];
[pool release];
}

希望这可以帮到你。愉快编码。

阿德里安

- Adrian P

Answer 3

我建议使用以下方法获取从开始日期到结束日期的时间组件。

这种方法比手动递减3个整数变量（小时，分钟和秒）更加优雅，因为这样做意味着你必须手动检查何时秒钟归零，必须手动将分钟重置为59等等。我曾经尝试过这种方法，效果不太好。

此外，当你最小化应用程序时，倒计时时钟会停止。如果你手动递减3个整数（小时，分钟和秒）来进行倒计时，最小化你的应用程序会导致倒计时出错。

由于这种方法自动计算两个日期之间的差异，即使应用程序从后台最小化状态返回，它也会自动重新计算剩余时间，而无需任何额外的代码。

-(void)viewDidLoad
{
    // instantiate a calendar object.
    gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateClock:) userInfo:nil repeats:YES];
    [countDownTimer fire];
}

-(void)updateClock:(NSTimer *)timer
{
    countDownDateFormatter = [[NSDateFormatter alloc] init];
    [countDownDateFormatter setDateFormat:@"hh:mm:ss"];

    NSDate *now = [NSDate date];

    NSDateComponents *comp = [gregorianCalendar components:NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit 
                                                  fromDate:now
                                                    toDate:countDownEndDate 
                                                   options:0];

    NSString *strTimeRemaining = nil;

    // if date have not expired
    if([now compare:countDownEndDate] == NSOrderedAscending)
    {
        strTimeRemaining = [[NSString alloc] initWithFormat:@"%02d:%02d:%02d", [comp hour],  [comp minute], [comp second]];
    }
    else 
    {
        // time has expired, set time to 00:00 and set boolean flag to no
        strTimeRemaining = [[NSString alloc] initWithString:@"00:00:00"];

        [countDownTimer invalidate];
        countDownTimer = nil;
    }

    lblCountDown.text = strTimeRemaining;

    [countDownDateFormatter release];
    [strTimeRemaining release];
}

- Zhang

---

这里的gregorianCalendar是什么？ - Dev

gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];在头文件(.h文件)中声明这个变量为NSCalendar *gregorianCalendar，并在viewDidLoad中实例化它。我已经更新了我的答案。 - Zhang