ios - NSDate 返回一个负的 NSTimeInterval

Question

我有以下代码:

- (void)pointsStartedDisplaying {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        dispatch_async(dispatch_get_main_queue(), ^{
            self.timeStartedDisplayingPoint = [NSDate date];
            self.stopButton.enabled = YES;

            [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateElapsedTime:) userInfo:nil repeats:YES];
        });
    });
}

- (void)updateElapsedTime:(NSTimer *)timer {
    NSTimeInterval elapsedTimeDisplayingPoints = [self.timeStartedDisplayingPoint timeIntervalSinceDate:[NSDate date]];
    self.elapsedTimeValueLabel.text = [NSString stringWithFormat:@"%f seconds", elapsedTimeDisplayingPoints];
}

但是，elapsedTimeDisplayingPoints 的值非常准确，只是每次都是负值。为什么它会返回 -3、-4、-5、 等？

Answer 1

If the receiver is earlier than anotherDate, the return value is negative .你的例子就是这种情况。您可以使用 fabs() 获得正值。