State loss

[nhaarman]

State loss can occur when a Scene transition occurs after the Activity has called onSaveInstanceState. If the Activity isn't restored after the transition occurred, the transition is lost and the application will be restored to the point it was in onSaveInstanceState.

Android's FragmentManager throws an exception if a transaction is executed after the state has been saved (commit) and allows you to ignore state loss (commitAllowingStateLoss). Currently, Acorn ignores state loss.

[nhaarman]

A solution could be to create our own state saving mechanism. If no Activity is active and a Scene transition occurs, a new call to the main Navigator's saveInstanceState could be done to avoid losing this state. This would result in an entirely custom state persistence layer just for Acorn.

The solution is more correct though: losing presentation state just because the UI layer isn't present is unwanted behavior. Since the application instance is kept alive when the Activity is gone for a certain period of time, it can be used to do this saving of state until the entire process is being killed.

A potential drawback could be that this state saving is costly when happening for every Scene transition.