How to determine the true final speed of panorama gestures?

Question

When used UIPanGestureRecognizerand detected UIGestureRecognizerStateEnded, gesture speed is not true speed. Instead, this is the old speed of the previous call to my action method. How can I access the true speed at the end of the gesture?

I create my UIPanGestureRecognizeras follows:

    UIPanGestureRecognizer* panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureRecognized:)];
    [panGestureRecognizer setMaximumNumberOfTouches:2];
    [panGestureRecognizer setMinimumNumberOfTouches:1];
    [panGestureRecognizer setDelegate:self];
    [panGestureRecognizer setDelaysTouchesBegan:NO];
    [panGestureRecognizer setDelaysTouchesEnded:NO];
    [panGestureRecognizer setCancelsTouchesInView:NO];
    [self addGestureRecognizer:panGestureRecognizer];

Beginning of my action:

- (IBAction) panGestureRecognized:(UIPanGestureRecognizer *)recognizer {

    UIGestureRecognizerState state = recognizer.state;

    CGPoint gestureTranslation = [recognizer translationInView:self];
    CGPoint gestureVelocity = [recognizer velocityInView:self];

    [CBAppDelegate log:@"panGestureRecognized: state: %s\n    translation: (%f, %f)\n    velocity: (%f, %f)", [self toString:state], gestureTranslation.x, gestureTranslation.y, gestureVelocity.x, gestureVelocity.y];

Log output example:

2013-09-30_10:46:32.830 panGestureRecognized: state: UIGestureRecognizerStateChanged
    translation: (-283.000000, 2.000000)
    velocity: (-43.046783, 45.551472)
2013-09-30_10:47:02.942 panGestureRecognized: state: UIGestureRecognizerStateEnded
    translation: (-283.000000, 2.000000)
    velocity: (-43.046783, 45.551472)

As you can see, the speed is the same in both entries of the magazine (the same story with the translation, but I only care about speed), although I held my finger for about 30 seconds without moving it, and then lifting the Finger. You can specify the time from timestamps of records. Of course, there should be no speed reported after 30 seconds without moving my finger.

iOS iPhone iOS 6.1.

Answer 1

velocityInView . , , . , .

, , , . - UIGestureRecognizerStateChanged UIGestureRecognizerStateEnded. , .

- (IBAction) panGestureRecognized:(UIPanGestureRecognizer *)recognizer {

    UIGestureRecognizerState state = recognizer.state;

    CGPoint gestureTranslation = [recognizer translationInView:self];
    CGPoint gestureVelocity = [recognizer velocityInView:self];

    if ( state == UIGestureRecognizerStateChanged )
         _lastChange = CFAbsoluteTimeGetCurrent();
    else if ( state == UIGestureRecognizerStateEnded ) {
         double curTime = CFAbsoluteTimeGetCurrent(); 
         double timeElapsed = curTime - _lastChange;
         if ( timeElapsed < MY_THRESHOLD )
              finalSpeed = gestureVelocity;
         else
              finalSpeed = CGPointZero;
    }   
 }

Answer 2

2019 ...

, :

...

var cat: CADisplayLink? = nil
var prevTime = CFAbsoluteTimeGetCurrent()
var lastKnownPosition: CGFloat = 0
var lastKnownActualVelocity: Double = 0

...

@objc func _checkVelocityEveryTrueFrame() {
    let newTime = CFAbsoluteTimeGetCurrent()
    let frameTime = newTime - prevTime
    prevTime = newTime

    let newPos = yourConstraint.constant
    lastKnownActualVelocity = Double(newPos - lastKnownPosition) / frameTime
    lastKnownPosition = newPos
    print("- \(frameTime) \(lastKnownPosition) \(lastKnownActualVelocity)")
}

@objc func dragOrFlick(_ p: UIPanGestureRecognizer) {
    if p.state == .began {
        cat?.invalidate()
        cat = nil
        cat = CADisplayLink(target: self,
             selector: #selector(_checkVelocityEveryTrueFrame))
        cat?.add(to: .main, forMode: .common)
    }

    if p.state == .changed {
        ... p.translation(in: ...
        yourConstraint.constant = new position...
    }

    if p.state == .ended {
        cat?.invalidate()
        cat = nil
        let trueFinalVelocity = lastKnownActualVelocity
        print("trueFinalVelocity is truly \(trueFinalVelocity)")
    }
}

. , .

⁺ . , ; : :/ .