Jazz Hands is a simple, keyframe based animation framework for UIKit. Animations can be controlled via gestures, scroll views, kvo, or ReactiveCocoa.

Jazz Hands is used extensively in IFTTT for iPhone, most famously in the app intro:

##Demo App

Run JazzHandsDemo/JazzHandsDemo.xcodeproj to see a simple demonstration of moving, resizing, fading, and hiding views in a scrolling app intro.

##Installation

It's recommended that you install from CocoaPods, but you may alternatively just copy the contents of /src into your project.

##Quick Start

First, add JazzHands to your UIViewController.

import "IFTTTJazzHands.h"

Now, create an Animator to manage all of the animations in this UIViewController.

@property (nonatomic, strong) IFTTTAnimator *animator;

// later...

self.animator = [IFTTTAnimator new];

Create an animation for a view that you want to animate. There are multiple types of animation that can be applied to a view. For this example, we'll use IFTTTFrameAnimation, which moves and sizes a view.

IFTTTFrameAnimation *frameAnimation = [IFTTTFrameAnimation new];
frameAnimation.view = viewThatYouWantToAnimate;

Register the animation with the animator.

[self.animator addAnimation:frameAnimation];

Add some keyframes to the animation. Let's move this view 140 pixels left, and double the size, between times 30 and 60.

[frameAnimation addKeyFrame:[[IFTTTAnimationKeyFrame alloc] initWithTime:30 andFrame:CGRectMake(10, 10, 100, 100)]];
[frameAnimation addKeyFrame:[[IFTTTAnimationKeyFrame alloc] initWithTime:60 andFrame:CGRectMake(150, 10, 200, 200)]];

Now, to animate the view, tell the animator what time it is. For example, to tie this animation to a UIScrollView, notify the animator of time in the scroller's delegate method.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
  [self.animator animate:scrollView.contentOffset.x];
}

This will produce an effect where the view will be at 10,10 and sized 100x100 for scroll positions 0 to 30. Between scroll positions 30 and 60, the view will grow and move until scroll position 61, where it will be locked to 150, 10 and 200x200.

##Animation Types

Jazz Hands supports several types of animations:

• IFTTTFrameAnimation moves and sizes views.
• IFTTTAlphaAnimation creates fade effects.
• IFTTTHideAnimation hides and shows views.
• IFTTTAngleAnimation for rotation effects.

##More Examples

###ReactiveCocoa

Say you want to perform some animations based on a UITableView's scroll offset, but you don't want to be the delegate for that table? ReactiveCocoa is perfect for that.

[RACObserve(self.tableView, contentOffset) subscribeNext:^(NSValue *value) {
  NSInteger y = floor(self.tableView.contentOffset.y);
  [self.animator animate:y];
}];

Or, maybe you want to animate some views based upon the position of another view? Jazz Hands works well with KVO.

- (void)viewDidLoad
{
  [self.viewToMirror addObserver:self 
                      forKeyPath:@"frame" 
                         options:NSKeyValueObservingOptionInitial 
                         context:nil];
}

- (void)observeValueForKeyPath:(NSString *)keyPath 
                      ofObject:(id)object 
                        change:(NSDictionary *)change 
                       context:(void *)context {

  if ([keyPath isEqualToString:@"frame"]) {
    [self.animator animate:CGRectGetMinY(self.viewToMirror.frame)];
  } else {
    [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
  }
}

Jazz Hands is flexible enough that it can accept timer input from many different types of sources, including UIGestureRecognizer.

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {
  [self.animator animate:[recognizer locationOfTouch:0 inView:self.view]];
}

An animator can only handle one animation per type per view. If you want multiple animations of the same type on a view, use keyframes.

Copyright 2013 IFTTT Inc