增加方法

lib/src/manager/im_message_manager.dart

@@ -816,6 +816,31 @@ class MessageManager {
         }));
   }
 
+  /// Fetch Surrounding Messages
+  /// [message] Message content
+  /// [before] message index - before
+  /// [after] message index - after
+  /// [operationID] Operation ID
+  Future<List<Message>> FetchSurroundingMessages({
+    required Message message,
+    int? before,
+    int? after,
+    String? operationID,
+  }) =>
+      _channel
+          .invokeMethod(
+              'fetchSurroundingMessages',
+              _buildParam({
+                'message': message.toJson(),
+                'before': before ?? 0,
+                'after': after ?? 0,
+                'operationID': Utils.checkOperationID(operationID),
+              }))
+          .then((value) {
+        final result = Utils.toListMap(value);
+        return List<Message>.from(result);
+      });
+
   static Map _buildParam(Map<String, dynamic> param) {
     param["ManagerName"] = "messageManager";
     param = Utils.cleanMap(param);