Chaining seperate animations that work on the same properties

Question

I have looked at Staggered animations for chaining animations but there they use one animation for one widget's properties, e.g. a opacity animation is controlling the fade in, but what if I want to first fade in and then later fade out that same widget? I mean I already have created the fade in animation and that is used for the widget opacity value like this:

_opacityDontWorry = Tween(
  begin: 0.0,
  end: 1.0,
).animate(
  CurvedAnimation(parent: _animationController, curve: Interval(0.0, 0.75, curve: Curves.easeIn)),
);

so those two are now bound together like this:

Opacity(
  opacity: _opacityDontWorry.value,
  child: Text("Don't worry"),
)

This work just fine and my Opacity get faded in, but after it is faded in I would like it to fade out after a short pause, but how can I do this? Do I create a new Tween and overwrite the _opacityDontWorry with that, or? Am I even on the right path here, how do I chain multiple animations that alter the same properties on a widget?

Thank you
Søren

Answer 1

May be this is a late answer. But a TweenSequence is the right class for animating the same attribute(s) mutations one after another. Docs reference.

Answer 2

You can use addStatusListener on your Animation. Check when the animation is completed and then call reverse() on your AnimationController.

If you want to, you can call reverse() inside a Future.delayed() for making a pause.

I've made this example for you:

import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> with TickerProviderStateMixin {
  AnimationController _animationController;
  Animation _opacityDontWorry;

  @override
  void initState() {
    super.initState();

    _animationController = AnimationController(duration: Duration(seconds: 1), vsync: this);
    _opacityDontWorry = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(
      CurvedAnimation(parent: _animationController, curve: Curves.easeIn),
    )..addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        Future.delayed(Duration(seconds: 3), () {
          _animationController.reverse();
        });
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton.extended(
        label: Text('Animate'),
        onPressed: () => _animationController.forward(),
      ),
      body: Center(
        child: AnimatedBuilder(
          animation: _opacityDontWorry,
          builder: (context, widget) {
            return Opacity(
              opacity: _opacityDontWorry.value,
              child: Text("Don't worry"),
            );
          },
        ),
      ),
    );
  }
}

UPDATE

In case you need to play this animation, and call another one after that, you can extract the opacity value to a variable. Then update that value from as many consecutive animations as you need.

  _firstAnimation = Tween(
    begin: 0.0,
    end: 1.0,
  ).animate(
    CurvedAnimation(parent: _animationController, curve: Interval(0.0, 0.20, curve: Curves.easeIn)),
  )..addListener(() {
      setState(() => _opacity = _firstAnimation.value);
    });

  // Leave an interval pause if you need
  _secondAnimation = Tween(
    begin: 1.0,
    end: 0.0,
  ).animate(
    CurvedAnimation(parent: _animationController, curve: Interval(0.40, 0.60, curve: Curves.easeIn)),
  )..addListener(() {
      setState(() => _opacity = _secondAnimation.value);
    });

In your widget's opacity property, instead of using _firstAnimation.value use _opacity.