基本完成

lib/widgets/common/app_backend.dart

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+import 'package:flutter/material.dart';
+
+class AppBackend extends StatelessWidget {
+  final Widget child;
+
+  const AppBackend({super.key, required this.child});
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      width: double.infinity,
+      padding: EdgeInsets.all(15),
+      decoration: BoxDecoration(
+        gradient: LinearGradient(
+          begin: Alignment.topLeft,
+          end: Alignment.bottomRight,
+          colors: [
+            Color(0xffdff8fb),
+            Color(0xffffffff),
+            Color(0xffdff8fb),
+          ],
+        ),
+      ),
+      child: SafeArea(child: child),
+    );
+  }
+}

lib/widgets/common/app_header.dart

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+import 'package:flutter/material.dart';
+
+class AppHeader extends StatefulWidget {
+  const AppHeader({super.key});
+
+  @override
+  State<AppHeader> createState() => _AppHeaderState();
+}
+
+class _AppHeaderState extends State<AppHeader> {
+  @override
+  Widget build(BuildContext context) {
+    return SafeArea(
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.spaceBetween,
+        children: [
+          Row(
+            spacing: 10,
+            children: [
+              Image.asset(
+                "assets/image/logo.png",
+                width: 44,
+              ),
+              Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Text(
+                    "FoodSafe",
+                    style: TextStyle(fontWeight: FontWeight.bold),
+                  ),
+                  Text(
+                    "AI Health Guardian",
+                    style: Theme.of(context).textTheme.labelSmall,
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}

lib/widgets/common/async_image.dart

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+import 'package:flutter/material.dart';
+
+class AsyncImage extends StatelessWidget {
+  final String url;
+  final double? width;
+
+  const AsyncImage({
+    super.key,
+    required this.url,
+    this.width,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      width: width,
+      child: Image.network(
+        url,
+        fit: BoxFit.cover,
+        // 加载中的样式
+        loadingBuilder: (context, child, loadingProgress) {
+          if (loadingProgress == null) {
+            return child; // 加载完成，直接返回图片
+          }
+          return Container(
+            color: Colors.grey[200],
+            alignment: Alignment.center,
+            child: CircularProgressIndicator(strokeWidth: 2),
+          );
+        },
+        // 加载失败的样式
+        errorBuilder: (context, error, stackTrace) {
+          return Container(
+            color: Colors.grey[200],
+            child: const Icon(
+              Icons.broken_image,
+              size: 30,
+              color: Colors.grey,
+            ),
+          );
+        },
+      ),
+    );
+  }
+}