重构example项目结构

example/lib/animated_category_item.dart

@@ -0,0 +1,39 @@
+import 'package:flutter/material.dart';
+
+class AnimatedCategoryItem extends StatelessWidget {
+  AnimatedCategoryItem({
+    required double startDelayFraction,
+    required this.controller,
+    required this.child,
+  }) : topPaddingAnimation = Tween(
+          begin: 0.0,
+          end: 16.0,
+        ).animate(
+          CurvedAnimation(
+            parent: controller,
+            curve: Interval(
+              0.000 + startDelayFraction,
+              0.400 + startDelayFraction,
+              curve: Curves.ease,
+            ),
+          ),
+        );
+
+  final Widget child;
+  final AnimationController controller;
+  final Animation<double> topPaddingAnimation;
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedBuilder(
+      animation: controller,
+      builder: (context, child) {
+        return Padding(
+          padding: EdgeInsets.only(top: topPaddingAnimation.value),
+          child: child,
+        );
+      },
+      child: child,
+    );
+  }
+}