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POCreating a continuous animation
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  1. POCreating a continuous animation
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    copied!<p>I want to create an animation that moves up or down the screen according to how fast the user taps the screen. The problem I am having is that I don't know how to create an infinite loop so I am firing a timer which presents issues. Here is my current code.</p> <pre><code>-(void)setPosOfCider { CGFloat originalY = CGRectGetMinY(cider.frame); float oY = originalY; float posY = averageTapsPerSecond * 100; float dur = 0; dur = (oY - posY) / 100; [UIImageView animateWithDuration:dur animations:^(void) { cider.frame = CGRectMake(768, 1024 - posY, 768, 1024); }]; } </code></pre> <p>Suggested fix(Doesn't work):</p> <pre><code> - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. scroll.pagingEnabled = YES; scroll.scrollEnabled = YES; scroll.contentSize = CGSizeMake(768 * 3, 1024); // 3 pages wide. scroll.delegate = self; self.speedInPointsPerSecond = 200000; self.tapEvents = [NSMutableArray array]; } -(void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; [self startDisplayLink]; } -(IBAction)tapped { [self.tapEvents addObject:[NSDate date]]; // if less than two taps, no average speed if ([self.tapEvents count] &lt; 1) return; // only average the last three taps if ([self.tapEvents count] &gt; 2) [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]; } - (void)startDisplayLink { self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(handleDisplayLink:)]; self.lastTime = CACurrentMediaTime(); [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; } - (CGFloat)yAxisValueBasedUponTapsPerSecond { CGFloat y = 1024 - (self.averageTapsPerSecond * 100.0); return y; } - (void)handleDisplayLink:(CADisplayLink *)displayLink { CFTimeInterval now = CACurrentMediaTime(); CGFloat elapsed = now - self.lastTime; self.lastTime = now; if (elapsed &lt;= 0) return; CGPoint center = self.cider.center; CGFloat destinationY = [self yAxisValueBasedUponTapsPerSecond]; if (center.y == destinationY) { // we don't need to move it at all return; } else if (center.y &gt; destinationY) { // we need to move it up center.y -= self.speedInPointsPerSecond * elapsed; if (center.y &lt; destinationY) center.y = destinationY; } else { // we need to move it down center.y += self.speedInPointsPerSecond * elapsed; if (center.y &gt; destinationY) center.y = destinationY; } self.cider.center = center; } </code></pre>
 

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