simple expandable widget

lib/widgets/expandable.dart

@@ -0,0 +1,91 @@
+import 'package:flutter/material.dart';
+
+enum ExpandableState {
+  expanded,
+  collapsed,
+}
+
+class Expandable extends StatefulWidget {
+  const Expandable({
+    Key? key,
+    required this.header,
+    required this.body,
+    this.animationController,
+    this.animation,
+    this.animationDurationMultiplier = 1.0,
+    this.onExpandChanged,
+  }) : super(key: key);
+
+  final Widget header;
+  final Widget body;
+  final AnimationController? animationController;
+  final Animation<double>? animation;
+  final double animationDurationMultiplier;
+  final void Function(ExpandableState)? onExpandChanged;
+
+  @override
+  State<Expandable> createState() => _ExpandableState();
+}
+
+class _ExpandableState extends State<Expandable> with TickerProviderStateMixin {
+  late final AnimationController animationController;
+  late final Animation<double> animation;
+  late final Duration duration;
+
+  Future<void> toggle() async {
+    if (animation.isDismissed) {
+      await animationController.forward();
+      widget.onExpandChanged?.call(ExpandableState.collapsed);
+    } else if (animation.isCompleted) {
+      await animationController.reverse();
+      widget.onExpandChanged?.call(ExpandableState.expanded);
+    }
+  }
+
+  @override
+  void initState() {
+    duration = Duration(
+      milliseconds: (500 * widget.animationDurationMultiplier).toInt(),
+    );
+    animationController = widget.animationController ??
+        AnimationController(
+          vsync: this,
+          duration: duration,
+        );
+    animation = widget.animation ??
+        Tween<double>(begin: 0.0, end: 1.0).animate(
+          CurvedAnimation(
+            curve: Curves.easeInOut,
+            parent: animationController,
+          ),
+        );
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    animationController.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        GestureDetector(
+          onTap: toggle,
+          child: Container(
+            color: Colors.transparent,
+            child: widget.header,
+          ),
+        ),
+        SizeTransition(
+          sizeFactor: animation,
+          axisAlignment: 1.0,
+          child: widget.body,
+        ),
+      ],
+    );
+  }
+}