外部图片，载入问题

Author: lymanzhao

lib/models/image_message.dart

@@ -1,33 +1,127 @@
 import 'dart:typed_data';
 import 'dart:convert';
 
+/// 图片消息元数据（不含图片数据）
+/// 用于快速加载历史记录，图片数据按需加载
 class ImageMessage {
   final String prompt;
-  final Uint8List image;
+  final String? imageRef; // 图片引用ID，不包含实际图片数据
   final String? aiDescription;
   final DateTime timestamp;
   final bool isSeparator;
 
-  ImageMessage(this.prompt, this.image, this.aiDescription, [DateTime? timestamp, this.isSeparator = false]) : timestamp = timestamp ?? DateTime.now();
+  ImageMessage({
+    required this.prompt,
+    this.imageRef,
+    this.aiDescription,
+    DateTime? timestamp,
+    this.isSeparator = false,
+  }) : timestamp = timestamp ?? DateTime.now();
 
+  /// 创建包含图片数据的完整消息（用于显示时）
+  ImageMessage withImageData(Uint8List imageData) {
+    return ImageMessage(
+      prompt: prompt,
+      imageRef: imageRef,
+      aiDescription: aiDescription,
+      timestamp: timestamp,
+      isSeparator: isSeparator,
+    ).._cachedImageData = imageData;
+  }
+
+  /// 缓存的图片数据（仅用于显示时）
+  Uint8List? _cachedImageData;
+
+  /// 获取缓存的图片数据
+  Uint8List? get cachedImageData => _cachedImageData;
+
+  /// 设置缓存的图片数据
+  void setCachedImageData(Uint8List data) {
+    _cachedImageData = data;
+  }
+
+  /// 清除缓存的图片数据
+  void clearCachedImageData() {
+    _cachedImageData = null;
+  }
+
+  /// 从JSON创建元数据（不含图片数据）
   factory ImageMessage.fromJson(Map<String, dynamic> json) {
+    return ImageMessage(
+      prompt: json['prompt'] as String,
+      imageRef: json['imageRef'] as String?,
+      aiDescription: json['aiDescription'] as String?,
+      timestamp: DateTime.parse(json['timestamp'] as String),
+      isSeparator: (json['isSeparator'] as bool?) ?? false,
+    );
+  }
+
+  /// 从旧格式JSON创建（兼容性，用于数据迁移）
+  factory ImageMessage.fromLegacyJson(Map<String, dynamic> json) {
     final prompt = json['prompt'] as String;
-    final imageBase64 = json['imageBase64'] as String;
-    final image = base64Decode(imageBase64) as Uint8List;
+    final imageBase64 = json['imageBase64'] as String?;
     final aiDescription = json['aiDescription'] as String?;
     final timestampStr = json['timestamp'] as String;
     final timestamp = DateTime.parse(timestampStr);
     final isSeparator = (json['isSeparator'] as bool?) ?? false;
-    return ImageMessage(prompt, image, aiDescription, timestamp, isSeparator);
+
+    // 旧格式包含图片数据，需要迁移
+    Uint8List? imageData;
+    if (imageBase64 != null && imageBase64.isNotEmpty) {
+      try {
+        imageData = base64Decode(imageBase64) as Uint8List;
+      } catch (e) {
+        print('Error decoding legacy image data: $e');
+      }
+    }
+
+    return ImageMessage(
+      prompt: prompt,
+      imageRef: null, // 旧格式没有imageRef，需要后续迁移
+      aiDescription: aiDescription,
+      timestamp: timestamp,
+      isSeparator: isSeparator,
+    ).._cachedImageData = imageData;
   }
 
+  /// 转换为JSON（只包含元数据）
   Map<String, dynamic> toJson() {
     return {
       'prompt': prompt,
-      'imageBase64': base64Encode(image),
+      'imageRef': imageRef,
       'aiDescription': aiDescription,
       'timestamp': timestamp.toIso8601String(),
       'isSeparator': isSeparator,
     };
   }
-}
+
+  /// 检查是否有图片
+  bool get hasImage => imageRef != null && imageRef!.isNotEmpty;
+
+  /// 检查是否有缓存的图片数据
+  bool get hasCachedImageData => _cachedImageData != null;
+
+  /// 复制消息
+  ImageMessage copyWith({
+    String? prompt,
+    String? imageRef,
+    String? aiDescription,
+    DateTime? timestamp,
+    bool? isSeparator,
+    bool clearCache = false,
+  }) {
+    // 深拷贝缓存的图片数据
+    Uint8List? copiedImageData;
+    if (!clearCache && _cachedImageData != null) {
+      copiedImageData = Uint8List.fromList(_cachedImageData!);
+    }
+    
+    return ImageMessage(
+      prompt: prompt ?? this.prompt,
+      imageRef: imageRef ?? this.imageRef,
+      aiDescription: aiDescription ?? this.aiDescription,
+      timestamp: timestamp ?? this.timestamp,
+      isSeparator: isSeparator ?? this.isSeparator,
+    ).._cachedImageData = copiedImageData;
+  }
+}

lib/models/image_session.dart

@@ -44,7 +44,7 @@ class ImageSession {
     return ImageSession(
       id: id ?? this.id,
       title: title ?? this.title,
-      messages: messages ?? this.messages,
+      messages: messages ?? List<ImageMessage>.from(this.messages),
       createdAt: createdAt ?? this.createdAt,
     );
   }