Snails provide a dataflow mini-language for animations and things like that.

What are they

Snails are almost like tweaks, but are used when changing a widget property takes time. A snail is defined by a function WidgetClass ⇒ Future[Unit].


Snails can be defined using the Snail companion object:

import macroid.Snail

// plays a sound
// and returns a future to track when it ends
def playSound = {
  val done = Promise[Unit]()
  // set up media player
  // play sound
  // when complete, call `done.success(())`

// set focus and play a sound
val focusLoudly = Snail[View] { view ⇒


Snails can be composed by using the ++ operator:

val wink = fadeIn ++ fadeOut

It is also possible to combine snails with tweaks by using either + or ++. More specifically, snails are added with ++, and tweaks are added with + (see Understanding operators):

def textAndFade(str: String) =
  text(str) ++ fadeIn

val fadeAndDisappear =
  fadeOut + hide


“Snailing” is a made-up word that denotes the process of applying snails to widgets. Snailing is very similar to tweaking, except it uses the <~~ operator:

textView <~~ fadeIn

It can be chained:

textView <~~ fadeIn <~~ fadeOut

Snailing can be also mixed with tweaking:

editText <~ text("foo") <~~ fadeIn <~ enable

It you want to apply the snail without waiting for it to finish, you can use <~. By the way, if you are confused about all these operators, check the Understanding operators section.

Snailing returns a UI action, to be more specific, a Ui[Future[...]].

Snailing workflows

By combining UI actions, we can program complex asynchronous snailing (and tweaking) workflows, for example:

(myProgressBar <~~ fadeOut(400)) ~~
(myTextView <~~ blink) ~~
(myOtherTextView <~ text("’SUP?"))

Note the use of ~~ operator: it denotes that we need to wait for completion of the action.

Standard snails

A number of standard snails are included. You can always find them in the scaladoc. Note that all these snails can be imported with import macroid.FullDsl._ or just import macroid.Snails._.

A quick rundown:

  • Basic snails
    • delay — wait for a given time
    • wait — wait for a given Future
  • Progress
    • waitProgress — modify a ProgressBar to track a Future or a list of Futures
  • Animation
    • anim — apply an animation
    • fadeIn — apply a fade-in
    • fadeOut — apply a fade-out