Flutter AnimationController – Floating Balloon Animation

AnimationController

The AnimationController class gives you increased flexibility in animation. The animation can be played forward or reverse, and you can stop it.

The AnimationController class produces linear values for a giving duration, and it tries to display a new frame at around 60 frames per second. The AnimationController class needs a Ticker-Provider class by passing the vsync argument in the constructor. The vsync prevents off-screen animations from consuming unnecessary resources.

AnimationController(duration: Duration(seconds: 4), vsync: this)

If the animation needs only one AnimationController, use SingleTickerProviderStateMixin. If the animation needs multiple AnimationControllers, use TickerProviderStateMixin. The Ticker class is driven by the ScheduleBinding.scheduleFrameCallback reporting once per animation frame. It is trying to sync the animation to be as smooth as possible.

class _AnimatedBalloonWidgetState extends State<AnimatedBalloonWidget> with SingleTickerProviderStateMixin {}

AnimationController Steps

The AnimationController class at first can seem complex to use because of the different classes needed. The following are the basic steps that you take to create a custom animation or multiple animations running at the same time.

1. Add AnimationController.
2. Add Animation.
3. Initiate AnimationController with Duration (milliseconds, seconds, and so on).
4. Initiate Animation with Tween with begin and end values and chain the animate method with a CurvedAnimation (for this example).
5. Use the AnimatedBuilder with Animation using a Container with a balloon to start Animation by calling the AnimationController.forward() and .reverse() to run the animation backward. The AnimatedBuilder widget is used to create a widget that performs a reusable animation.

As you can see, once you break down the steps, it becomes more manageable and less complicated.

Using Staggered Animations

A staggered animation triggers visual changes in sequential order. The animation changes can occur one after the other; they can have gaps without animations and overlap each other. One AnimationController class controls multiple Animation objects that specify the animation in a timeline (Interval).

Animation<double> _animationFloatUp;Animation<double> _animationGrowSize;

Now you’ll walk through an example of using one AnimationController class and the Interval() curve property to start different animations at different times. As noted in the preceding section, a staggered animation uses Interval() to begin and end animations sequentially or to overlap one another.

Interval(0.0, 1.0, curve: Curves.fastOutSlowIn)Interval(0.0, 0.75, curve: Curves.elasticInOut)

How It Works

Declaring SingleTickerProviderStateMixin to the AnimatedBalloonWidget widget class allows you to set the AnimationController vsync argument. The SingleTickerProviderStateMixin allows only one AnimationController. You added AnimationController and declared the _controller variable to animate both the floating upward or downward and the inflation or deflation of the balloon.

You declared the _animationFloatUp variable to hold the value from the Tween animation to show the balloon either floating upward or downward by setting the top margin of the Container widget. You also declared the _animationGrowSize variable to hold the value from the Tween animation to show the balloon either inflating or deflating by setting the width value of the Container widget.

The AnimatedBuilder constructor takes animation, builder, and child arguments. Next, you passed the _animationFloatUp animation to the AnimatedBuilder constructor. The AnimatedBuilder builder argument returns a Container widget with the child as an Image wrapped in a GestureDetector widget.

You used one AnimationController class with multiple Animation classes to create staggered animations.

AnimationController

This creates custom animations by using TickerProviderStateMixin, SingleTickerProviderStateMixin, AnimationController, Animation, Tween, and CurvedAnimation.