refactor(api): 统一响应解析并修复下载错误文案空白

各 *Api 类此前各自实现 data 结构判断，download_api 在结构异常时抛出空
message，界面会显示空白提示。抽出 ResponseDecoders 提供对象、可空对象、
对象数组三种语义，七个文件改为复用；下载侧异常文案与其他接口对齐。

lib/core/data/remote/account_api.dart

@@ -4,6 +4,7 @@ import '../models/account_device.dart';
 import '../models/account_export.dart';
 import '../models/account_profile.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 个人中心接口：`/app/me*`。
 class AccountApi {
@@ -23,11 +24,9 @@ class AccountApi {
 
   Future<List<AccountDevice>> devices() async {
     final data = await _client.get('/app/me/devices');
-    if (data is! List) return const [];
-    return [
-      for (final item in data)
-        if (item is Map) AccountDevice.fromJson(item.cast<String, dynamic>()),
-    ];
+    return ResponseDecoders.asMapList(
+      data,
+    ).map(AccountDevice.fromJson).toList();
   }
 
   Future<AccountExport> export() async {
@@ -47,6 +46,7 @@ class AccountApi {
     await _client.post('/app/me/deactivate/cancel');
   }
 
+  /// 个人资料允许缺失：后端未返回对象时按空对象解析，页面用默认值兜底。
   Map<String, dynamic> _map(Object? data) =>
-      data is Map ? data.cast<String, dynamic>() : const {};
+      ResponseDecoders.tryMap(data) ?? const {};
 }

lib/core/data/remote/catalog_api.dart

@@ -6,6 +6,7 @@ import '../models/page_result.dart';
 import '../models/playlist_detail.dart';
 import '../models/search_result.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 客户端目录接口，对应后端 `/app/**`。
 class CatalogApi {
@@ -14,11 +15,15 @@ class CatalogApi {
   final ApiClient _client;
 
   Future<HomeFeed> homeFeed() async {
-    return HomeFeed.fromJson(_asMap(await _client.get('/app/home/feed')));
+    return HomeFeed.fromJson(
+      ResponseDecoders.asMap(await _client.get('/app/home/feed')),
+    );
   }
 
   Future<HomeFeed> discoverFeed() async {
-    return HomeFeed.fromJson(_asMap(await _client.get('/app/discover/feed')));
+    return HomeFeed.fromJson(
+      ResponseDecoders.asMap(await _client.get('/app/discover/feed')),
+    );
   }
 
   /// 推荐流；types/categoryId 为空表示不过滤，cursor 为上一页末条。
@@ -29,7 +34,7 @@ class CatalogApi {
     int size = 10,
   }) async {
     return FeedPage.fromJson(
-      _asMap(
+      ResponseDecoders.asMap(
         await _client.get(
           '/app/feed',
           query: {
@@ -58,7 +63,7 @@ class CatalogApi {
         'pageSize': '$pageSize',
       },
     );
-    return SearchResult.fromJson(_asMap(data));
+    return SearchResult.fromJson(ResponseDecoders.asMap(data));
   }
 
   static const int playlistPageSize = 10;
@@ -86,7 +91,7 @@ class CatalogApi {
     int pageSize = playlistDramaPageSize,
   }) async {
     return PlaylistDetail.fromJson(
-      _asMap(
+      ResponseDecoders.asMap(
         await _client.get(
           '/app/playlists/$id',
           query: {
@@ -138,20 +143,13 @@ class CatalogApi {
 
   Future<Drama> dramaDetail(String dramaId) async {
     return Drama.fromDetailJson(
-      _asMap(await _client.get('/app/dramas/$dramaId')),
+      ResponseDecoders.asMap(await _client.get('/app/dramas/$dramaId')),
     );
   }
 
   List<ContentCategory> _categories(Object? data) {
-    if (data is! List) return const [];
-    return [
-      for (final item in data)
-        if (item is Map<String, dynamic>) ContentCategory.fromJson(item),
-    ];
-  }
-
-  Map<String, dynamic> _asMap(Object? data) {
-    if (data is Map<String, dynamic>) return data;
-    throw const ApiException(-1, '返回数据格式异常');
+    return ResponseDecoders.asMapList(
+      data,
+    ).map(ContentCategory.fromJson).toList();
   }
 }

lib/core/data/remote/category_api.dart

@@ -4,6 +4,7 @@ import '../models/content_category.dart';
 import '../models/drama.dart';
 import '../models/page_result.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 内容分类接口，对应契约 `GET /app/categories`。
 class CategoryApi {
@@ -16,11 +17,9 @@ class CategoryApi {
   /// 拉取已启用分类，id 全程按字符串解析。
   Future<List<ContentCategory>> list() async {
     final data = await _client.get('/app/categories');
-    if (data is! List) return const [];
-    return [
-      for (final item in data)
-        if (item is Map<String, dynamic>) ContentCategory.fromJson(item),
-    ];
+    return ResponseDecoders.asMapList(
+      data,
+    ).map(ContentCategory.fromJson).toList();
   }
 
   /// 分类下已上线短剧，pageIndex 从 1 开始。

lib/core/data/remote/commerce_api.dart

@@ -4,6 +4,7 @@ import '../models/order.dart';
 import '../models/product.dart';
 import '../models/wallet.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 金币与解锁接口，对应契约 §1.8。
 class CommerceApi {
@@ -13,8 +14,7 @@ class CommerceApi {
 
   Future<WalletSnapshot> wallet() async {
     final data = await _client.get('/app/wallet');
-    if (data is Map<String, dynamic>) return WalletSnapshot.fromJson(data);
-    throw const ApiException(-1, '返回数据格式异常');
+    return WalletSnapshot.fromJson(ResponseDecoders.asMap(data));
   }
 
   /// 上架商品列表；`type` 传 `COIN_PACK` 或 `VIP`。
@@ -23,13 +23,9 @@ class CommerceApi {
       '/app/products',
       query: type == null ? null : {'type': type},
     );
-    if (data is List) {
-      return data
-          .whereType<Map<String, dynamic>>()
-          .map(AppProduct.fromJson)
-          .toList();
-    }
-    throw const ApiException(-1, '返回数据格式异常');
+    return ResponseDecoders.requiredMapList(
+      data,
+    ).map(AppProduct.fromJson).toList();
   }
 
   /// 创建充值订单，返回 `CREATED` 状态订单。
@@ -38,13 +34,11 @@ class CommerceApi {
       '/app/orders',
       body: {'productId': productId},
     );
-    if (data is Map<String, dynamic>) return AppOrder.fromJson(data);
-    throw const ApiException(-1, '返回数据格式异常');
+    return AppOrder.fromJson(ResponseDecoders.asMap(data));
   }
 
   Future<UnlockResult> unlock(String episodeId) async {
     final data = await _client.post('/app/episodes/$episodeId/unlock');
-    if (data is Map<String, dynamic>) return UnlockResult.fromJson(data);
-    throw const ApiException(-1, '返回数据格式异常');
+    return UnlockResult.fromJson(ResponseDecoders.asMap(data));
   }
 }

lib/core/data/remote/download_api.dart

@@ -3,6 +3,7 @@
 import '../models/download_license.dart';
 import '../models/download_policy.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 离线下载授权接口，对应契约 §1.6 的全部 8 个接口。
 ///
@@ -15,7 +16,7 @@ class DownloadApi {
   /// 拉取配额和偏好策略。
   Future<DownloadPolicy> policy() async {
     return DownloadPolicy.fromJson(
-      _asMap(await _client.get('/app/downloads/policy')),
+      ResponseDecoders.asMap(await _client.get('/app/downloads/policy')),
     );
   }
 
@@ -30,7 +31,7 @@ class DownloadApi {
   /// 申请下载授权；同集重复申请由服务端保证幂等。
   Future<DownloadLicense> grant(String episodeId, {String? quality}) async {
     return DownloadLicense.fromJson(
-      _asMap(
+      ResponseDecoders.asMap(
         await _client.post(
           '/app/downloads',
           body: {'episodeId': episodeId, 'quality': ?quality},
@@ -42,17 +43,17 @@ class DownloadApi {
   /// 拉取当前设备的授权列表。
   Future<List<DownloadLicense>> list() async {
     final data = await _client.get('/app/downloads');
-    if (data is! List) return const [];
-    return [
-      for (final item in data)
-        if (item is Map<String, dynamic>) DownloadLicense.fromJson(item),
-    ];
+    return ResponseDecoders.asMapList(
+      data,
+    ).map(DownloadLicense.fromJson).toList();
   }
 
   /// 续传前刷新短时效下载地址。
   Future<DownloadLicense> refreshUrl(String episodeId) async {
     return DownloadLicense.fromJson(
-      _asMap(await _client.get('/app/downloads/$episodeId/url')),
+      ResponseDecoders.asMap(
+        await _client.get('/app/downloads/$episodeId/url'),
+      ),
     );
   }
 
@@ -67,7 +68,7 @@ class DownloadApi {
     String? errorMsg,
   }) async {
     return DownloadLicense.fromJson(
-      _asMap(
+      ResponseDecoders.asMap(
         await _client.post(
           '/app/downloads/$episodeId/progress',
           body: {
@@ -93,9 +94,4 @@ class DownloadApi {
     final data = await _client.delete('/app/downloads');
     return data is int ? data : 0;
   }
-
-  Map<String, dynamic> _asMap(Object? data) {
-    if (data is Map<String, dynamic>) return data;
-    throw const ApiException(-1, '');
-  }
 }

lib/core/data/remote/playback_api.dart

@@ -3,6 +3,7 @@
 import '../models/episode_stats.dart';
 import '../models/play_ticket.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 播放票据接口：`GET /app/episodes/{id}/play`（契约 §1.4）。
 ///
@@ -15,14 +16,12 @@ class PlaybackApi {
 
   Future<PlayTicket> ticket(String episodeId) async {
     final data = await _client.get('/app/episodes/$episodeId/play');
-    if (data is Map<String, dynamic>) return PlayTicket.fromJson(data);
-    throw const ApiException(-1, '返回数据格式异常');
+    return PlayTicket.fromJson(ResponseDecoders.asMap(data));
   }
 
   /// 轻量刷新互动计数：不签发地址，也不占用播放票据缓存。
   Future<EpisodeStats> episodeStats(String episodeId) async {
     final data = await _client.get('/app/episodes/$episodeId/stats');
-    if (data is Map<String, dynamic>) return EpisodeStats.fromJson(data);
-    throw const ApiException(-1, '返回数据格式异常');
+    return EpisodeStats.fromJson(ResponseDecoders.asMap(data));
   }
 }

lib/core/data/remote/response_decoders.dart

@@ -0,0 +1,49 @@
+// Author: fruit.com.cn
+
+import 'api_exception.dart';
+
+/// 接口响应 `data` 字段的统一解析。
+///
+/// 此前每个 `*_api.dart` 各写一份 `is Map` 判断与错误文案，还出现过抛空
+/// message 导致界面显示空白的情况；统一收口到这里，语义只有三种：
+/// 必须为对象、可为空对象、对象数组。
+abstract final class ResponseDecoders {
+  /// 业务失败码：HTTP 成功但 `data` 结构不符合约定。
+  static const int malformedCode = -1;
+
+  /// `data` 结构异常时的提示，可直接展示给用户。
+  static const String malformedMessage = '返回数据格式异常';
+
+  /// 要求 `data` 是对象，否则抛 [ApiException]。
+  static Map<String, dynamic> asMap(Object? data) {
+    final map = tryMap(data);
+    if (map == null) {
+      throw const ApiException(malformedCode, malformedMessage);
+    }
+    return map;
+  }
+
+  /// 允许缺失：`data` 为空或不是对象时返回 null。
+  static Map<String, dynamic>? tryMap(Object? data) {
+    if (data is Map<String, dynamic>) return data;
+    if (data is Map) return data.cast<String, dynamic>();
+    return null;
+  }
+
+  /// 对象数组；不是数组时按空列表处理，避免列表页因结构异常白屏。
+  static List<Map<String, dynamic>> asMapList(Object? data) {
+    if (data is! List) return const [];
+    return data
+        .whereType<Map>()
+        .map((item) => item.cast<String, dynamic>())
+        .toList();
+  }
+
+  /// 对象数组；不是数组时抛 [ApiException]，用于不能静默为空的数据（如商品）。
+  static List<Map<String, dynamic>> requiredMapList(Object? data) {
+    if (data is! List) {
+      throw const ApiException(malformedCode, malformedMessage);
+    }
+    return asMapList(data);
+  }
+}

lib/core/data/remote/watch_api.dart

@@ -3,6 +3,7 @@
 import '../models/page_result.dart';
 import '../models/watch_progress.dart';
 import 'api_client.dart';
+import 'response_decoders.dart';
 
 /// 观看进度接口：`/app/watch/*`（契约 §1.5）。支持账号或设备身份。
 class WatchApi {
@@ -28,7 +29,8 @@ class WatchApi {
         'source': source,
       },
     );
-    return data is Map<String, dynamic> ? WatchProgress.fromJson(data) : null;
+    final map = ResponseDecoders.tryMap(data);
+    return map == null ? null : WatchProgress.fromJson(map);
   }
 
   /// 某部剧的续看位置；没有记录时后端返回空 data。
@@ -37,7 +39,8 @@ class WatchApi {
       '/app/watch/progress',
       query: {'dramaId': dramaId},
     );
-    return data is Map<String, dynamic> ? WatchProgress.fromJson(data) : null;
+    final map = ResponseDecoders.tryMap(data);
+    return map == null ? null : WatchProgress.fromJson(map);
   }
 
   /// 最近观看分页：`pageIndex`/`pageSize`，解包 `PageResult`。
@@ -49,13 +52,9 @@ class WatchApi {
       '/app/watch/recent',
       query: {'pageIndex': '$pageIndex', 'pageSize': '$pageSize'},
     );
-    if (data is! Map) {
-      return const PageResult();
-    }
-    return PageResult.fromJson(
-      Map<String, dynamic>.from(data),
-      WatchProgress.fromJson,
-    );
+    final map = ResponseDecoders.tryMap(data);
+    if (map == null) return const PageResult();
+    return PageResult.fromJson(map, WatchProgress.fromJson);
   }
 
   /// 删除某部剧的观看记录（记录页清单条用）。