UIView+EasingFunctions

This is a category on UIView that allows to attach custom easing functions to animatable UIView properties.

UIView+EasingFunctions works great with AHEasing, a library of easing functions. The library contains almost every easing function you might ever need.

Of course you can write your own easing functions as well.

Easing functions?

Easing functions specify the rate of change of a parameter over time. Objects in real life don’t just start and stop instantly, and almost never move at a constant speed. When we open a drawer, we first move it quickly, and slow it down as it comes out. Drop something on the floor, and it will first accelerate downwards, and then bounce back up after hitting the floor.

from easings.net (you should probably check the site, it does a great job explaining and illustrating various easing functions)

Installation

###Cocoapods###

Cocoapods is an Objective-C library manager.

Adding UIView+EasingFunctions to your project using Cocoapods is as easy as adding the following line to your Podfile:

pod 'UIView+EasingFunctions'

UIView+EasingFunctions podspec automatically adds AHEasing to the project as well. If that's not something you want, use pod 'UIView+EasingFunctions/Bare' instead.

###Manually###

1. Download and unarchive.
2. Drag and drop UIView+EasingFunctions subfolder, containing UIView+EasingFunctions.h and .m files into your Xcode project's Project Navigator (left pane), click Finish.
3. Add QuartzCore.framework to your project's Link Binary With Libraries build phase.

Usage

Let's say you want to make a bouncy frame animation:

#import <UIView+EasingFunctions/UIView+EasingFunctions.h>

#import <AHEasing/easing.h>

/* ... */

[view setEasingFunction:BounceEaseOut forKeyPath:@"frame"];

That's it. Now any frame animation of this view will use BounceEaseOut easing function (defined in AHEasing/easing.h):

[UIView animateWithDuration:.5 animations:^{
    
    view.frame = CGRectMake(10, 110, 100, 32);
    
}];

What if you only want one specific animation block to be affected? Use the completion block to remove the easing function:

[UIView animateWithDuration:.6 animations:^{
    
    [view setEasingFunction:ElasticEaseOut forKeyPath:@"center"];
    
    view.center = CGPointMake(160, 415);
    
} completion:^(BOOL finished) {
    
    [view removeEasingFunctionForKeyPath:@"center"];
    
}];

There's a sample app project available (make sure to open .xcworkspace file, not the .xcodeproj).

What properties are supported?

All animatable properties of UIView.

Gotchas

Animating backgroundColor between two colors in different color spaces (including pattern images) won't do any good.

How it works

It swizzles addAnimation:forKey: of the view's backing CALayer.

Acknowledgement

The entire idea of hijacking the backing layer's addAnimation:forKey: comes from this blog post by Evadne Wu.

License

Do whatever you want.