We can implement Flutter animations manually or with Animated Builder, but if we only need to implement animations for Container only, there is a short way to do that with AnimatedContainer widget.

1. Create new AnimatedContainer

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   @override
     Widget build(BuildContext context) {
    return AnimatedContainer(
      duration: const Duration( // duration
        milliseconds: 300,
      ),
      curve: Curves.easeIn, // animation
      child: const Center(
        child: Text('Hello World!'),
      ),
      height: triggeredValue ? 500 : 300, // trigger by value
    );
     }
   }
   

With this short way, you do not need to explicit animation controller, animation widget and ticker provider mixin.