我的秒表出现NSTimer问题

Question

这是我的问题，当我点击开始按钮时，计时器运行，当我点击停止按钮时，它停止。然而，当我点击"开始"按钮时，它会回到零。我希望启动按钮在计时器停止的地方继续。

.h
NSTimer *stopWatchTimer;
    NSDate *startDate;
    @property (nonatomic, retain) IBOutlet UILabel *stopWatchLabel;
    - (IBAction)onStartPressed;
    - (IBAction)onStopPressed;
    - (IBAction)onResetPressed;
.m
    - (void)updateTimer
    {
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"HH:mm:ss.SSS"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString=[dateFormatter stringFromDate:timerDate];
    stopWatchLabel.text = timeString;
    }
    - (IBAction)onStartPressed {
    startDate = [NSDate date];
    // Create the stop watch timer that fires every 10 ms
    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
    target:self
    selector:@selector(updateTimer)
    userInfo:nil
    repeats:YES];
    }
    - (IBAction)onStopPressed {
    [stopWatchTimer invalidate];
    stopWatchTimer = nil;
    [self updateTimer];
    }
    - (IBAction)onResetPressed {
    stopWatchLabel.text = @”00:00:00:000″;
    }

请帮忙感谢

Answer 1

您在处理状态时遇到问题。一种状态是启动按钮被按下，但重置按钮在它之前没有被按下。另一种状态则是启动按钮已被按下，重置按钮已在它之前被按下。你可以做的一件事是创建一个iVar来跟踪这种状态。所以使用这样的BOOL：

首先声明iVar:

BOOL resetHasBeenPushed;

将值初始化为NO。

然后进行

 - (IBAction)onResetPressed {
    stopWatchLabel.text = @”00:00:00:000″;
    resetHasBeenPushed = YES;

现在，您需要在某个时刻将其设置回NO，这可能在启动方法中完成：

- (IBAction)onStartPressed {
    startDate = [NSDate date];
    // Create the stop watch timer that fires every 10 ms
    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
    target:self
    selector:@selector(updateTimer)
    userInfo:nil
    repeats:YES];
    resetHasBeenPushed = NO;
}
    }

顺便说一句，如果您在iVar中制作NSDateFormatter，则不需要重复初始化它。在代码中移动以下行，或者在这里只运行一次：

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"HH:mm:ss.SSS"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];

更新

试试这个：

- (IBAction)onStartPressed {
    if (resetHasBeenPushed== YES) {
        startDate = [NSDate date];  // This will reset the "clock" to the time start is set
    }
    // Create the stop watch timer that fires every 10 ms
    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
    target:self
    selector:@selector(updateTimer)
    userInfo:nil
    repeats:YES];
    }