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 IF and DO by IFTTT for iPhone and iPad, most famously in the app intro.

##Demo App

Open JazzHandsDemo.xcworkspace to see a simple demonstration of moving, scaling, fading, and transforming views in a scrolling app intro.

To run the example project, clone the repo, and run pod install from the Example directory.

##JazzHands in Swift

Looking to incorporate Jazz Hands into your Swift project? Check out RazzleDazzle, our brand new scrolling keyframe animations library reimagined in Swift.

##Installation

JazzHands is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "JazzHands"

You may alternatively just copy the contents of the JazzHands folder 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 IFTTTAlphaAnimation, which fades a view in and out.

IFTTTAlphaAnimation *alphaAnimation = [IFTTTAlphaAnimation animationWithView: viewThatYouWantToAnimate];

Register the animation with the animator.

[self.animator addAnimation: alphaAnimation];

Add some keyframes to the animation. Let's fade this view out between times 30 and 60.

[alphaAnimation addKeyframeForTime:30 alpha:1.f];
[alphaAnimation addKeyframeForTime:60 alpha:0.f];

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
{
  [super scrollViewDidScroll:scrollView];
  [self.animator animate:scrollView.contentOffset.x];
}

This will produce an effect where the view will be fully faded in and visible for scroll positions 0 to 30. Between scroll positions 30 and 60, the view will fade out to be invisible, and it will stay faded out for scroll positions greater than 60.

##Animation Types

Jazz Hands supports several types of animations:

• IFTTTAlphaAnimation animates the alpha property (creates fade effects).
• IFTTTRotationAnimation animates a rotation transform in degrees (for rotation effects).
• IFTTTBackgroundColorAnimation animates the backgroundColor property.
• IFTTTCornerRadiusAnimation animates the layer.cornerRadius property.
• IFTTTHideAnimation animates the hidden property (hides and shows views).
• IFTTTScaleAnimation applies a scaling transform (to scale view sizes).
• IFTTTTranslationAnimation applies a translation transform (to translate view position).
• IFTTTTransform3DAnimation animates the layer.transform property (for 3D transforms).
• IFTTTTextColorAnimation animates the textColor property of a UILabel.
• IFTTTFillColorAnimation animates the fillColor property of a CAShapeLayer.
• IFTTTStrokeStartAnimation animates the strokeStart property of a CAShapeLayer (does not work with IFTTTStrokeEndAnimation).
• IFTTTStrokeEndAnimation animates the strokeEnd property of a CAShapeLayer (does not work with IFTTTStrokeStartAnimation).
• IFTTTPathPositionAnimation animates the layer.position property of a UIView.
• IFTTTConstraintConstantAnimation animates an AutoLayout constraint constant.
• IFTTTConstraintMultiplierAnimation animates an AutoLayout constraint constant as a multiple of an attribute of another view (to offset or resize views based on another view's size)
• IFTTTScrollViewPageConstraintAnimation animates an AutoLayout constraint constant to place a view on a scroll view page (to position views on a scrollView using AutoLayout)
• IFTTTFrameAnimation animates the frame property (moves and sizes views. Not compatible with AutoLayout).

##More Examples

Easy Paging Scrollview Layouts in an AutoLayout World

JazzHands's keepView:onPage: method of the IFTTTAnimatedPagingScrollViewController is a super easy way to lay out a paging scroll view that does what you expect it to when your app is rotated or used in the new split-screen iPad views of iOS9, a notoriously tricky aspect of getting your apps fully AutoLayout-ready. JazzHands sets up an AutoLayout-friendly paging scroll view controller for you, and all you need to do to make your layout respond properly to any view size changes is tell JazzHands which page you'd like things on.

As a bonus, because it's built on top of the animations library, you can even tell JazzHands that you'd like one of your views to show up on multiple pages while other views scroll past, with a single call to keepView:onPages:.

To see the new JazzHands 2.0 AutoLayout magic in action, check out the example project.

###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) {
	CGFloat y = self.tableView.contentOffset.y;
	[self.animator animate:y];
}];

KVO

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];
  }
}

Gestures

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].x];
}

Notes

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.

IFTTTFrameAnimation is not compatible with AutoLayout or any of the constraint animations.

Looking for libraries to build awesome keyframe animations like JazzHands on Android? Check out SparkleMotion.

Contributors

• Devin Foley, creator.
• Laura Skelton

Contributing

1. Fork it ( https://github.com/[my-github-username]/JazzHands/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Copyright 2015 IFTTT Inc.