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;

这是我的计时器在视图中加载

_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

，此值继续执行

目标： - 倒计时直到零并停止计时器实际上我将在倒计时结束后隐藏标签

更新： -

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

初始化了上面的计时器

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

您的行动方法无效。

如果传递参数，则它必须是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NSNumber

之类的对象

Answer 2

创建属性

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<body ng-app="myApp" ng-controller="myCrtl">

<select ng-model="selectedItem" ng-options="item.login for item in data.items"></select>
<br>Selected Item:{{selectedItem}}
</body>

@property (nonatomic) int secondsLeft;

中的

viewDidLoad

选择器：

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

Answer 3

有几件事。

正如vadian所说，如果使用基于选择器的计时器，计时器处理程序函数将获取一个参数，该参数是对计时器本身的引用。如果要跟踪倒计时，可以定义属性以跟踪它：

@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，如果您还需要支持iOS 9及更早版本，那么您必须使用上述基于选择器的解决方案。

我建议不要依赖计时器来调整时间，因为您不能确保以您想要的频率调用计时器。在上面的两个例子中，我捕捉到我倒计时的时间，并且只显示＆＃34;现在＆＃34;之间的时间量。那个预定的＆＃34;停止时间＆＃34;。
请注意，我还建议你不要自己构建格式字符串。这是一个方便的NSDateComponentsFormatter，可以为您格式化。如果可以，请使用它。
您制作了计时器参考strong。您可以将其设为weak，因为计划的计时器在invalidated之前不会被取消分配。一旦它invalidated，就可以自动为您解除分配。

NSTimer倒计时无法正常运行

3 个答案: