Creating Custom Animations in Flutter

Are you tired of using the same pre-built animations offered by Flutter? Do you want to create something completely unique that really pops on your app? Then, you've come to the right place!

In this tutorial, we'll be diving deep into creating custom animations in Flutter. We'll look at how to create animations from scratch, how to use implicit and explicit animations, how to create advanced animations using physics, and much more. So, let's get started!

The Basics of Animation

Before we dive into creating custom animations, it's essential to understand the basics of animation in Flutter. Animation is essential to making user interfaces come alive, and creating user experiences that are engaging and memorable. Animations help provide feedback, convey state changes, and subtly guide users to interact with various UI elements in your app.

In Flutter, there are two primary types of animations: implicit animations and explicit animations. Implicit animations are built into widgets like AnimatedContainer, AnimatedOpacity, and AnimatedCrossFade. Explicit animations are created using the AnimationController class and can be fully customized to create unique effects.

Let's start with implicit animations.

Implicit Animations

Implicit animations can be used to create simple animations without having to create a custom animation class. They are built into many of Flutter's built-in widgets, like AnimatedContainer, AnimatedOpacity, and AnimatedCrossFade. For example, to create a simple opacity animation using AnimatedOpacity, you can do the following:

AnimatedOpacity(
  opacity: _opacityValue,
  duration: Duration(milliseconds: 500),
  child: Text('Animated Text'),
),

The widget works by taking a value (in this case, _opacityValue) and animating it over time to the specified values. In this example, _opacityValue could be an AnimationController, and the duration specifies how long it should take to animate the value from 0 to 1.

Implicit animations are great for simple effects, but they don't offer the same level of customization as explicit animations. For that, we need to create our own custom animations using AnimationController.

Explicit Animations

Creating custom animations with AnimationController requires a bit more code, but it offers great flexibility and endless possibilities. An AnimationController class can control one or more Animation<double> objects, each of which represents a value that changes over time. To create an explicit animation using an AnimationController, follow these steps:

Step 1: Create the AnimationController

The first step is to create an AnimationController. You can specify the duration of the animation and whether it should repeat or not.

AnimationController _animationController = AnimationController(
  duration: Duration(milliseconds: 1000),
  vsync: this,
);

In this example, we create an animation controller with a duration of 1 second, and we specify a TickerProviderStateMixin as the vsync. The vsync tells the animation controller which widget to sync to. It's usually one that's visible on the screen.

Step 2: Create the Animations

Next, we create the animations. There are various classes of animation that can be used, depending on the type of effect we want to create.

Animation<double> _opacityAnimation = Tween<double>(
  begin: 0.0,
  end: 1.0,
).animate(_animationController);

This example uses the Tween class to create an animation that goes from an opacity value of 0.0 to 1.0. We attach this animation to the _animationController.

The Tween class is a handy class that helps create animations between two values with automatic interpolation. However, it's essential to note that there are many other types of animations, such as CurvedAnimation for animating with easing curves, and RadialAnimation for creating circular animations.

Step 3: Add Listeners

Adding listeners to an animation can help you track its progress and update the UI accordingly.

_animationController.addListener(() {
  setState(() {});
});

In this example, we add a listener that calls setState each time the _animationController updates its state. You can use this listener to update the UI based on the current value of the animation.

Step 4: Animate!

Finally, we can animate the animation using the _animationController.

_animationController.forward();

In this example, we call the forward method that tells the _animationController to animate the animation forward. We can also reverse the animation or stop it using the stop method.

Customizing Animations

With the basics of animation down, we can now start creating more complex and customized animations. Here are some of the advanced techniques that we can use to customize our animations further:

Adding a Curve

Adding an easing curve to an animation can give it a more natural feel with acceleration and deceleration.

Animation<double> _animationWithCurve = CurvedAnimation(
  parent: _animationController,
  curve: Curves.easeInOut,
);

Here we're using the CurvedAnimation class to create a new animation that's controlled by _animationController and has easing applied using Curves.easeInOut.

Physics-based Animations

Physically-based animations offer a way to create more natural-looking effects. Flutter provides physics-based animations through the Flubber library.

final simulation = SpringSimulation(
  SpringDescription(
    mass: 1,
    stiffness: 50,
    damping: 1,
  ),
  0,
  100,
  -200,
);

AnimationController _springAnimation = AnimationController(
  duration: const Duration(seconds: 3),
  vsync: this,
)..animateWith(simulation); 

This example uses the SpringSimulation class to create a simulation for a spring-like effect. We then create an AnimationController, pass in the simulation, and the animation controller will automatically handle the physics of the spring simulation.

Animating Multiple Values

We can also use animations to animate multiple values at once. For example, we can alter the size, position, and color of a widget at once.

Animation<double> _opacity = Tween(begin: 0.1, end: 1.0).animate(CurvedAnimation(
        parent: _animationController,
        curve: Curves.easeIn,
      ));

      Animation<double> _scale = Tween(begin: 0.0, end: 1.0).animate(CurvedAnimation(
        parent: _animationController,
        curve: Curves.easeOut,
      ));

      Animation<Offset> _position = Tween<Offset>(
        begin: const Offset(0.0, 0.0),
        end: const Offset(3.0, 0.0),
      ).animate(CurvedAnimation(
        parent: _animationController,
        curve: Curves.fastOutSlowIn,
      ));

      Animation<Color> _color = ColorTween(
        begin: Colors.white.withOpacity(0.0),
        end: Colors.white,
      ).animate(_animationController);

In this example, we create new Animation objects - _scale, _position, and _color - for different properties of the widget. The animations are then added as listeners to the _animationController.

You can use the value of each animation to update the corresponding property of the widget in the setState method.

Conclusion

Custom animations are a crucial aspect of creating engaging user interfaces for your app. We hope this tutorial has given you a good understanding of how to get started with custom animations in Flutter.

We explored the different types of animation, the basics of creating explicit animations, and how to customize them. As you practice creating custom animations, you'll be able to create unique and memorable user interactions that will separate your app from the rest.

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