触摸测量不起作用

Question

我正在尝试实现一些代码来衡量用户触摸屏幕的时间，触摸之间的时间和触摸量。用户触摸屏幕的时间非常好。但是，触摸量始终等于1，触摸之间的时间总是nan。我在这里做错了什么？

首先我做：

@property (nonatomic, strong) NSDate *touchStart;
@property (nonatomic, strong) NSDate *touchFinish;
@property (nonatomic) NSTimeInterval touchTime;

@property (nonatomic, strong) NSDate *untouchStart;
@property (nonatomic, strong) NSDate *untouchFinish;
@property (nonatomic) NSTimeInterval untouchTime;

@property (nonatomic, assign) NSInteger numberOfTouched;

然后：

- (void)viewDidLoad
{
    self.untouchStart = [NSDate date];
    self.numberOfTouched = 0;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesBegan:touches withEvent:event];
    self.backgroundColorBackup = self.backgroundColor;
    self.backgroundColor = self.tintColor;
    UIColor *textColor = ([self.backgroundColorBackup isEqual:[UIColor clearColor]] ?
                          [self.class averageContentColor] : self.backgroundColorBackup);
    self.numberLabel.textColor = textColor;
    self.lettersLabel.textColor = textColor;

    self.touchStart = [NSDate date];
    self.untouchFinish = [NSDate date];
    self.untouchTime = [self.untouchFinish timeIntervalSinceDate:self.untouchStart];

    NSLog(@"This button was touched after: %f", self.untouchTime);
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesEnded:touches withEvent:event];
    [self resetHighlight];

    self.numberOfTouched = self.numberOfTouched + 1;

    self.touchFinish = [NSDate date];
    self.touchTime = [self.touchFinish timeIntervalSinceDate:self.touchStart];

    NSLog(@"This button was touched for: %f", self.touchTime);
    self.untouchStart = [NSDate date];

    NSLog(@"The number of buttons touched is: %ld", (long)self.numberOfTouched);
}