NSTimer 倒计时无法正常运行

Question

我正在尝试区分时间并在 ui 标签中向用户显示倒数计时器

NSTimer

的声明

@property (strong, nonatomic)NSTimer *timer;

这是我看到的计时器已加载

_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(updateCountdown:) userInfo:nil repeats: YES];

这是我的 updateCountdown 方法

-(void) updateCountdown:(int)secondsLeft {
    int hours, minutes, seconds;

    secondsLeft--;
    hours = secondsLeft / 3600;
    minutes = (secondsLeft % 3600) / 60;
    seconds = (secondsLeft %3600) % 60;
    _countDownlabel.text = [self timeFormatted:secondsLeft];///[NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
    NSLog(@"%@",[NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds]);
    if ( secondsLeft == 0 ) {
        [_timer invalidate];
      }
    }

我的日志详细信息是

2017-06-30 09:49:34.070 Barebones[845:56963] requestReply cust liqour category: {
date = "30-6-2017";
"end_time" = "11:41";
"market_crash" = true;
"start_time" = "09:41";
}
2017-06-30 09:49:34.070 Barebones[845:56963] true
2017-06-30 09:49:34.070 Barebones[845:56963] 09:41
2017-06-30 09:49:34.070 Barebones[845:56963] 11:41
2017-06-30 09:49:34.070 Barebones[845:56963] 30-6-2017
2017-06-30 09:49:34.073 Barebones[845:56963] 2016-12-25 08:58:00 +0000
2017-06-30 09:49:34.073 Barebones[845:56963] 2016-12-25 12:15:00 +0000
2017-06-30 09:49:34.073 Barebones[845:56963] 197.000000 is the time  difference
2017-06-30 09:49:34.073 Barebones[845:56963] 00:03:17
2017-06-30 09:49:35.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:36.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:37.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:38.075 Barebones[845:56963] 991:05:35

这个值继续执行

目标：- 倒计时到零并停止计时器实际上我会在倒计时结束后隐藏标签

更新：-

 int secondsLeft=[self timeFormatted:[date2 timeIntervalSinceDate:date1]/60];

上面的定时器已经初始化

这是我更新的计时器：-

int secondsLeft=[date2 timeIntervalSinceDate:date1]/60;

NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
                                  [NSNumber numberWithInt:secondsLeft], @"cID", nil];
_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(updateCountdown:) userInfo:userInfo repeats: YES];

这是我更新的计时器方法：-

- (void)updateCountdown:(NSTimer *)timer{
int hours, minutes, seconds;
NSDictionary *userInfo = [timer userInfo];
int secondsLeft = [[userInfo objectForKey:@"cID"] intValue];
secondsLeft--;

hours = secondsLeft / 3600;
minutes = (secondsLeft % 3600) / 60;
seconds = (secondsLeft %3600) % 60;
_countDownlabel.text = [self timeFormatted:secondsLeft];///[NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
NSLog(@"%@",[NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds]);
if ( secondsLeft == 0 ) {
    [_timer invalidate];
  }
}

Answer 1

你的操作方法不可行。

如果传递的参数必须是NSTimer实例

- (void)updateCountdown:(NSTimer *)timer

要传递自定义参数，请使用 userInfo 参数。

然而，更合适的解决方案是使用实例变量或属性，因为 userInfo 的值必须是一个对象，例如 NSNumber

Answer 2

创建属性

@property (nonatomic) int secondsLeft;

在viewDidLoad

self.secondsLeft = 5 * 60; // 5 minutes
_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(updateCountdown) userInfo:nil repeats: YES];

选择器：

-(void)updateCountdown{
    int secondsLeft = self.secondsLeft;
    if (secondsLeft >= 0) {
        int minutes, seconds;
        int hours;
        self.secondsLeft--;

        hours = secondsLeft / 3600;
        minutes = (secondsLeft % 3600) / 60;
        seconds = (secondsLeft %3600) % 60;
        NSString *time = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
        _countDownlabel.text = [self timeFormatted:secondsLeft];
    }
    if (secondsLeft <= 0) {
        NSLog(@"TIME ENDS");
        if ([self.timer isValid]) {
            [self.timer invalidate];
            self.timer = nil;
        }
    }
}

Answer 3

几件事。

正如 vadian 所说，如果您使用基于选择器的计时器，则计时器处理函数采用单个参数，该参数是对计时器本身的引用。如果你想跟踪倒计时，你可以定义属性来跟踪：

@interface ViewController ()

@property (nonatomic, weak) IBOutlet UILabel *label;
@property (nonatomic, weak) NSTimer *timer;
@property (nonatomic, strong) NSDateComponentsFormatter *formatter;
@property (nonatomic, strong) NSDate *stopTime;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.formatter = [[NSDateComponentsFormatter alloc] init];
    self.formatter.allowedUnits = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    self.formatter.unitsStyle = NSDateComponentsFormatterUnitsStylePositional;
    self.formatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;

    self.stopTime = [[NSDate date] dateByAddingTimeInterval:5 * 60];   // in 5 minutes, for example

    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(handleTimer:) userInfo:nil repeats:true];

    [self.timer fire];    // don't wait one second before firing the first time; fire now
}

- (void)handleTimer:(NSTimer *)timer {
    NSDate *now = [NSDate date];
    if ([now compare:self.stopTime] == NSOrderedDescending) {
        // do whatever you want when timer stops

        [timer invalidate];
        return;
    }

    self.label.text = [self.formatter stringFromDate:now toDate:self.stopTime];
}

// Note, when the view disappears, invalidate the timer so the timer doesn't
// keep strong reference to the view controller. Note that in this selector-based
// pattern, I can't attempt to do this in `dealloc`, because the scheduled timer
// will keep a strong reference, preventing `dealloc` from getting called. So do 
// this in `viewDidDisappear`.

- (void)viewDidDisappear:(BOOL)animated {
    [self.timer invalidate];
}

@end

如果仅支持 iOS 10 及更高版本，我建议使用完成块计时器，因为它进一步简化了过程：

@interface ViewController ()

@property (nonatomic, weak) IBOutlet UILabel *label;
@property (nonatomic, weak) NSTimer *timer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSDateComponentsFormatter *formatter = [[NSDateComponentsFormatter alloc] init];
    formatter.allowedUnits = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    formatter.unitsStyle = NSDateComponentsFormatterUnitsStylePositional;
    formatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;

    NSDate *stopTime = [[NSDate date] dateByAddingTimeInterval:5 * 60];  // in 5 minutes, for example
    typeof(self) __weak weakSelf = self; // make sure to not reference `self` in block below, but only reference `weakSelf` to avoid timer from maintaining strong reference

    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:true block:^(NSTimer * _Nonnull timer) {
        NSDate *now = [NSDate date];
        if ([now compare:stopTime] == NSOrderedDescending) {
            // do whatever you want when timer stops

            [timer invalidate];
            return;
        }

        weakSelf.label.text = [formatter stringFromDate:now toDate:stopTime];
    }];

    [self.timer fire];    // don't wait one second before firing the first time; fire now
}

// Because I was careful to not reference `self` inside the above block, 
// this block-based timer will NOT keep a strong reference to the view
// controller. Nonetheless, when the view controller is dismissed, I want
// to stop the timer, to avoid wasting CPU cycles on a timer that isn't
// needed anymore.

- (void)dealloc {
    [self.timer invalidate];
}

@end

显然，如果您也需要支持 iOS 9 和更早版本，那么您必须使用上述基于选择器的解决方案。

我建议不要依赖定时器来调整时间，因为你不能保证定时器会以你想要的频率被调用。在上面的两个例子中，我捕捉到我正在倒计时的时间，并且只显示 "now" 和预定的 "stop time".
注意，我还建议您不要自己构建格式字符串。有一个方便的 NSDateComponentsFormatter 可以为您格式化。如果可以，请使用它。
您创建了计时器参考 strong。您可以将其设置为 weak，因为计划的计时器在 invalidated 之前不会被释放。一旦它是 invalidated，自动为您解除分配就很方便了。

NSTimer 倒计时无法正常运行

NSTimer countdown not functioning correctly

ios

objective-c

timer

nstimer