Animated Constraint (Instead of AnimatedContainer)

animated_constraints.dart

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class AnimatedConstraints extends ImplicitlyAnimatedWidget {
  const AnimatedConstraints({
    super.key,
    required this.constraints,
    required super.duration,
    super.curve,
    this.child,
    super.onEnd,
  });
  final BoxConstraints constraints;
  final Widget? child;

  @override
  AnimatedWidgetBaseState<AnimatedConstraints> createState() =>
      _AnimatedConstraintsState();

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(
      DiagnosticsProperty<BoxConstraints>(
        'constraints',
        constraints,
        defaultValue: null,
        showName: false,
      ),
    );
  }
}

class _AnimatedConstraintsState
    extends AnimatedWidgetBaseState<AnimatedConstraints> {
  BoxConstraintsTween? _constraints;

  @override
  void forEachTween(TweenVisitor<Object?> visitor) {
    _constraints =
        visitor(_constraints, widget.constraints, (value) {
              return BoxConstraintsTween(begin: value! as BoxConstraints);
            })
            as BoxConstraintsTween?;
  }

  @override
  Widget build(BuildContext context) {
    return ConstrainedBox(
      constraints: _constraints?.evaluate(animation) ?? const BoxConstraints(),
      child: widget.child,
    );
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder description) {
    super.debugFillProperties(description);
    description.add(
      DiagnosticsProperty<BoxConstraintsTween>(
        'constraints',
        _constraints,
        showName: false,
        defaultValue: null,
      ),
    );
  }
}