1. override
void update(double t)

Sets the action to a specific point in time. The t value that is passed in is a normalized value 0.0 to 1.0 of the duration of the action. Every action will always recieve a callback with the end time point (1.0), unless it is cancelled.

Source

@override
void update(double t) {
  fire();
  _finished = true;
}