Keyframes is an open source tool and library from Facebook that allows you to convert Adobe After Effects shape based animations to a format which can then be loaded by the included library on both iOS and Android.
Keyframe images are vector based so they can be resized without losing image quality, feature very high quality animations with great detail, and a small file size. Keyframes was designed because engineers wanted to display Facebook reaction animations with maximum animation detail on a wide variety of devices.
You can find more about Keyframes over on the Facebook code site.
In addition to Adobe After Effects you will need the Adobe ExtendScript Toolkit.
You can find Keyframes on Github here.
A great tool for creating iOS animations.