willowtreeapps/spruce-android

Spruce is an Android library that helps coordinate animations across multiple views at the same time. On a screen with many elements, getting each item to animate at the right moment, in the right order, and with the right delay can become complicated to manage by hand. Spruce takes care of that coordination: you give it a group of views, specify how you want them sorted, and assign an animation, and the library figures out the timing for each individual element. The library works through two main concepts. The first is a sort function, which controls the order in which views begin animating. Eight built-in sort functions cover common patterns: top-to-bottom linear, radial (spreading outward from the center), random, cornered, inline, and a few variations. You can also write a custom sort function if none of the built-in options fits. The second concept is the animation itself, which uses Android's standard Animator class. Spruce includes a small set of ready-made animations (fade in, fade out, shrink) for common cases, but you can supply any custom Animator. The API is a builder chain: you attach a view group, a sort function, and one or more animators, then call .start(). An inter-object delay value controls how much time passes between each successive view starting its animation, which produces the wave or cascade effect that makes multi-view animations look polished. The library also includes a view exclusion feature for skipping specific views or list positions from the animation, useful when certain elements should animate independently or stay still. Spruce is added to an Android project through Gradle and has a companion iOS version in a separate repository. It is released under the MIT license.