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copied!<p>An even simpler approach is to employ the <a href="https://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/UIView/UIView.html#//apple_ref/doc/c_ref/UIViewAnimationOptions" rel="nofollow"><code>UIViewAnimationOptionBeginFromCurrentState</code></a> option when using block-based animations:</p> <pre><code>[UIView animateWithDuration:2.0 delay:0.0 options:UIViewAnimationOptionBeginFromCurrentState | UIViewAnimationOptionAllowUserInteraction animations:^{ // set the new frame } completion:NULL]; </code></pre> <p>That stops the current block-based animation and starts the new one from the current location. Note, effective iOS 8 and later, this is now the default behavior, generally obviating the need for the <code>UIViewAnimationOptionBeginFromCurrentState</code> altogether. In fact, the default behavior considers not only the position of the view in question, but also the current velocity, ensuring a smooth transition. See WWDC 2014 video <a href="https://developer.apple.com/videos/wwdc/2014/?id=236" rel="nofollow">Building Interruptible and Responsive Interactions</a> for more information.)</p> <hr> <p>Another approach would be to have your taps (which adjust the <code>averageTapsPerSecond</code>) to stop any existing animation, grab the view's current <code>frame</code> from the presentation layer (which reflects the state of the view mid-animation), and then just start a new animation:</p> <pre><code>// grab the frame from the presentation layer (which is the frame mid-animation) CALayer *presentationLayer = self.viewToAnimate.layer.presentationLayer; CGRect frame = presentationLayer.frame; // stop the animation [self.viewToAnimate.layer removeAllAnimations]; // set the frame to be location we got from the presentation layer self.viewToAnimate.frame = frame; // now, starting from that location, animate to the new frame [UIView animateWithDuration:3.0 delay:0.0 options:UIViewAnimationOptionCurveLinear animations:^{ self.viewToAnimate.frame = ...; // set the frame according to the averageTapsPerSecond } completion:nil]; </code></pre> <p>In iOS 7, you would use the rendition of <code>animateWithDuration</code> with the <code>initialSpringVelocity:</code> parameter, to ensure a smooth transition from the object's current movement to the new animation. See the aforementioned <a href="https://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/UIView/UIView.html#//apple_ref/doc/c_ref/UIViewAnimationOptions" rel="nofollow">WWDC video</a> for examples.</p> <hr> <p>Original answer:</p> <p>To adjust a view on the basis of the number of taps per second, you could use a <code>CADisplayLink</code>, which is like a <code>NSTimer</code>, but ideally suited for animation efforts like this. Bottom line, translate your <code>averageTapsPerSecond</code> into a <code>y</code> coordinate, and then use the <code>CADisplayLink</code> to animate the moving of some view to that <code>y</code> coordinate:</p> <pre><code>#import "ViewController.h" #import <QuartzCore/QuartzCore.h> @interface ViewController () @property (nonatomic, strong) CADisplayLink *displayLink; @property (nonatomic) CFTimeInterval lastTime; @property (nonatomic) CGFloat speedInPointsPerSecond; @property (nonatomic, strong) NSMutableArray *tapEvents; @property (nonatomic) CGFloat averageTapsPerSecond; @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; self.speedInPointsPerSecond = 200.0; self.tapEvents = [NSMutableArray array]; UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)]; [self.view addGestureRecognizer:tap]; } - (void)handleTap:(UITapGestureRecognizer *)gesture { [self.tapEvents addObject:[NSDate date]]; // if less than two taps, no average speed if ([self.tapEvents count] < 2) return; // only average the last three taps if ([self.tapEvents count] > 3) [self.tapEvents removeObjectAtIndex:0]; // now calculate the average taps per second of the last three taps NSDate *start = self.tapEvents[0]; NSDate *end = [self.tapEvents lastObject]; self.averageTapsPerSecond = [self.tapEvents count] / [end timeIntervalSinceDate:start]; } - (CGFloat)yAxisValueBasedUponTapsPerSecond { CGFloat y = 480 - self.averageTapsPerSecond * 100.0; return y; } - (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; [self startDisplayLink]; } - (void)viewDidDisappear:(BOOL)animated { [super viewDidDisappear:animated]; [self stopDisplayLink]; } - (void)startDisplayLink { self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(handleDisplayLink:)]; self.lastTime = CACurrentMediaTime(); [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; } - (void)stopDisplayLink { [self.displayLink invalidate]; self.displayLink = nil; } - (void)handleDisplayLink:(CADisplayLink *)displayLink { CFTimeInterval now = CACurrentMediaTime(); CGFloat elapsed = now - self.lastTime; self.lastTime = now; if (elapsed <= 0) return; CGPoint center = self.viewToAnimate.center; CGFloat destinationY = [self yAxisValueBasedUponTapsPerSecond]; if (center.y == destinationY) { // we don't need to move it at all return; } else if (center.y > destinationY) { // we need to move it up center.y -= self.speedInPointsPerSecond * elapsed; if (center.y < destinationY) center.y = destinationY; } else { // we need to move it down center.y += self.speedInPointsPerSecond * elapsed; if (center.y > destinationY) center.y = destinationY; } self.viewToAnimate.center = center; } @end </code></pre> <p>Hopefully this illustrates the idea.</p> <p>Also, to use the above, make sure you've added the QuartzCore framework to your project (though in Xcode 5, it seems to do that for you).</p> <hr> <p>For standard, constant speed animation, you can use the following:</p> <p>You would generally do this with an animation that repeats (i.e. <code>UIViewAnimationOptionRepeat</code>) and that autoreverses (i.e. <code>UIViewAnimationOptionAutoreverse</code>):</p> <pre><code>[UIView animateWithDuration:1.0 delay:0.0 options:UIViewAnimationOptionAutoreverse | UIViewAnimationOptionRepeat animations:^{ cider.frame = ... // specify the end destination here } completion:nil]; </code></pre> <p>For a simple up-down-up animation, that's all you need. No timers needed.</p>

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