AnimationController is one of the most used Flutter animation classes. It is derived from Animation<double> class and adds some fundamental methods for manipulating animations. The Animation class is the basis of animation in Flutter; as said before, it does not have any animation control-related methods. AnimationController adds these controls to the animation concept, such as the following:

• Play and stop controls: AnimationController adds the ability to play the animation forward, backward, or stop it
• Duration: Real animations have a finite time to play, that is, they play for a while and finish, or repeat
• Allows setting the animation current value: This causes a stop of the animation and notifies the status and value listeners
• Allows defining the upper and lower bound of the animation: This is so that we can know the deemed values before and after playing the animation

Let's check the AnimationController constructor and analyze its main properties:

AnimationController({
    double value,
    Duration duration,
    String debugLabel,
    double lowerBound: 0.0,
    double upperBound: 1.0,
    AnimationBehavior animationBehavior: AnimationBehavior.normal,
    @required TickerProvider vsync
})

As you can see, some properties are self-explanatory, but let's review them:

• value: This is the initial value of the animation, and it defaults to lowerBound if not specified.
• duration: This is the duration of the animation.
• debugLabel: This is a string to help during debugging. It identifies the controller in debug output.
• lowerBound: This cannot be null; it is the smallest value of the animation in which it is deemed to be dismissed, typically the start value when running.
• upperBound: Also, this cannot be null; it is the largest value of the animation at which it is deemed to be complete, typically the end value when running.
• animationBehavior: This configures how AnimationController behaves when animations are disabled. If it's AnimationBehavior.normal, the animation duration will be reduced, and if it's AnimationBehavior.preserve, AnimationController will preserve its behavior.
• vsync: This is a TickerProvider instance the controller will use to obtain a signal whenever a frame triggers.