前端：

1、更新界面图标
2、修改消息缓存逻辑
3、新增清空未读消息数
后端：
1、修复不同时区导致的时间显示问题
2、新增清空未读消息数接口

backend/IM_API/Application/EventHandlers/ConversationEventHandler.cs

@@ -46,8 +46,10 @@ namespace IM_API.Application.EventHandlers
                 }
                 userAConversation.LastMessage = @event.MessageContent;
                 userAConversation.LastReadMessageId = @event.MessageId;
+                userAConversation.LastMessageTime = @event.MessageCreated;
                 userBConversation.LastMessage = @event.MessageContent;
                 userBConversation.UnreadCount += 1;
+                userBConversation.LastMessageTime = @event.MessageCreated;
                 _context.UpdateRange(userAConversation,userBConversation);
                 await _context.SaveChangesAsync();
             }

backend/IM_API/Application/EventHandlers/SignalREventHandler.cs

@@ -23,7 +23,17 @@ namespace IM_API.Application.EventHandlers
         {
             if(@event.ChatType == Models.ChatType.PRIVATE)
             {
-                MessageBaseDto messageBaseDto = _mapper.Map<MessageBaseDto>(_mapper.Map<Message>(@event));
+                MessageBaseDto messageBaseDto = new MessageBaseDto
+                {
+                    MsgId = @event.MessageId.ToString(),
+                    ChatType = @event.ChatType.ToString(),
+                    Content = @event.MessageContent,
+                    GroupMemberId = null,
+                    ReceiverId = @event.MsgRecipientId,
+                    SenderId = @event.MsgSenderId,
+                    TimeStamp = @event.MessageCreated,
+                    Type = @event.MessageMsgType.ToString()
+                };
                 await _hub.Clients.Users(@event.MsgRecipientId.ToString()).SendAsync("ReceiveMessage", messageBaseDto);
             }
         }

backend/IM_API/Configs/MapperConfig.cs

@@ -41,7 +41,7 @@ namespace IM_API.Configs
             CreateMap<FriendRequestDto, FriendRequest>()
                 .ForMember(dest => dest.RequestUser , opt => opt.MapFrom(src => src.FromUserId))
                 .ForMember(dest => dest.ResponseUser , opt => opt.MapFrom(src => src.ToUserId))
-                .ForMember(dest => dest.Created , opt => opt.MapFrom(src => DateTime.Now))
+                .ForMember(dest => dest.Created , opt => opt.MapFrom(src => DateTime.UtcNow))
                 .ForMember(dest => dest.StateEnum , opt => opt.MapFrom(src => FriendRequestState.Pending))
                 .ForMember(dest => dest.Description , opt => opt.MapFrom(src => src.Description))
                 ;
@@ -101,7 +101,7 @@ namespace IM_API.Configs
                 .ForMember(dest => dest.TargetId, opt => opt.MapFrom(src => src.MsgRecipientId))
                 .ForMember(dest => dest.UnreadCount, opt => opt.MapFrom(src => 0))
                 .ForMember(dest => dest.StreamKey, opt => opt.MapFrom(src => src.StreamKey))
-                .ForMember(dest => dest.LastMessageTime, opt => opt.MapFrom(src => DateTime.Now))
+                .ForMember(dest => dest.LastMessageTime, opt => opt.MapFrom(src => DateTime.UtcNow))
                 ;
 
             //创建会话对象

backend/IM_API/Hubs/ChatHub.cs

@@ -60,5 +60,17 @@ namespace IM_API.Hubs
             }
             return;
         }
+        public async Task ClearUnreadCount(int conversationId)
+        {
+            if (!Context.User.Identity.IsAuthenticated)
+            {
+                await Clients.Caller.SendAsync("ReceiveMessage", new BaseResponse<object?>(CodeDefine.AUTH_FAILED));
+                Context.Abort();
+                return;
+            }
+            var userIdStr = Context.User.FindFirstValue(ClaimTypes.NameIdentifier);
+            await _conversationService.ClearUnreadCountAsync(int.Parse(userIdStr), conversationId);
+            return;
+        }
     }
 }

backend/IM_API/Interface/Services/IConversationService.cs

@@ -35,5 +35,12 @@ namespace IM_API.Interface.Services
         /// <param name="conversationId"></param>
         /// <returns></returns>
         Task<ConversationDto> GetConversationByIdAsync(int userId, int conversationId);
+        /// <summary>
+        /// 清空未读消息
+        /// </summary>
+        /// <param name="userId"></param>
+        /// <param name="conversationId"></param>
+        /// <returns></returns>
+        Task<bool> ClearUnreadCountAsync(int userId, int conversationId);
     }
 }

backend/IM_API/Program.cs

@@ -3,6 +3,7 @@ using IM_API.Configs;
 using IM_API.Filters;
 using IM_API.Hubs;
 using IM_API.Models;
+using IM_API.Tools;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.IdentityModel.Tokens;
@@ -103,6 +104,10 @@ namespace IM_API
             builder.Services.AddControllers(options =>
             {
                 options.Filters.Add<GlobalExceptionFilter>();
+            }).AddJsonOptions(options =>
+            {
+                // 保持 ISO 8601 格式
+                options.JsonSerializerOptions.Converters.Add(new UtcDateTimeConverter());
             });
             builder.Services.AddModelValidation(configuration);
             // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle

backend/IM_API/Services/ConversationService.cs

@@ -118,5 +118,21 @@ namespace IM_API.Services
             return dto;
         }
         #endregion
+
+        public async Task<bool> ClearUnreadCountAsync(int userId, int conversationId)
+        {
+            var conversation = await _context.Conversations.FirstOrDefaultAsync(x => x.UserId == userId && x.Id == conversationId);
+            if (conversation is null) throw new BaseException(CodeDefine.CONVERSATION_NOT_FOUND);
+            var message = await _context.Messages
+                .Where(x => x.StreamKey == conversation.StreamKey)
+                .OrderByDescending(x => x.Id)
+                .FirstOrDefaultAsync();
+            conversation.LastReadMessage = message;
+            conversation.UnreadCount = 0;
+            _context.Conversations.Update(conversation);
+            await _context.SaveChangesAsync();
+            return true;
+
+        }
     }
 }

backend/IM_API/Tools/UTCConverter.cs

@@ -0,0 +1,18 @@
+using System.Text.Json;
+
+namespace IM_API.Tools
+{
+    public class UtcDateTimeConverter : System.Text.Json.Serialization.JsonConverter<DateTime>
+    {
+        public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            => reader.GetDateTime();
+
+        public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
+        {
+            // 如果 Kind 已经是 Utc，直接输出。
+            // 如果不是，先 SpecifyKind 再输出，确保不会发生时区偏移计算
+            var utcDate = value.Kind == DateTimeKind.Utc ? value : DateTime.SpecifyKind(value, DateTimeKind.Utc);
+            writer.WriteStringValue(utcDate.ToString("yyyy-MM-ddTHH:mm:ssZ"));
+        }
+    }
+}