Future<Null> repeat({double min, double max, Duration period })

Starts running this animation in the forward direction, and restarts the animation when it completes.

Defaults to repeating between the lower and upper bounds.

Source 

Future<Null> repeat({ double min, double max, Duration period }) {
  min ??= lowerBound;
  max ??= upperBound;
  period ??= duration;
  assert(() {
    if (duration == null) {
      throw new FlutterError(
        'AnimationController.repeat() called with no explicit Duration and default Duration.\n'
        'Either the "duration" argument to the repeat() method should be provided, or the '
        '"duration" property should be set, either in the constructor or later, before '
        'calling the repeat() function.'
      );
    }
    return true;
  });
  return animateWith(new _RepeatingSimulation(min, max, period));
}