An interface implemented by classes that can vend Ticker objects.
Tickers can be used by any object that wants to be notified whenever a frame
triggers, but are most commonly used indirectly via an
AnimationController. AnimationControllers need a TickerProvider to
obtain their Ticker. If you are creating an AnimationController from a
State, then you can use the TickerProviderStateMixin and
SingleTickerProviderStateMixin classes to obtain a suitable
TickerProvider. The widget test framework
WidgetTester object can be
used as a ticker provider in the context of tests. In other contexts, you
will have to either pass a TickerProvider from a higher level (e.g.
indirectly from a State that mixes in TickerProviderStateMixin), or
create a custom TickerProvider subclass.
Abstract const constructor. This constructor enables subclasses to provide
const constructors so that they can be used in const expressions.