前端：

增加会话缓存
后端：
增加触发消息创建事件
增加消息创建事件触发后的处理函数

backend/IM_API/Application/EventHandlers/SignalREventHandler.cs

@@ -1,6 +1,9 @@
-using IM_API.Application.Interfaces;
+using AutoMapper;
+using IM_API.Application.Interfaces;
 using IM_API.Domain.Events;
+using IM_API.Dtos;
 using IM_API.Hubs;
+using IM_API.Models;
 using IM_API.Tools;
 using Microsoft.AspNetCore.SignalR;
 
@@ -9,15 +12,20 @@ namespace IM_API.Application.EventHandlers
     public class SignalREventHandler : IEventHandler<MessageCreatedEvent>
     {
         private readonly IHubContext<ChatHub> _hub;
-        public SignalREventHandler(IHubContext<ChatHub> hub)
+        private readonly IMapper _mapper;
+        public SignalREventHandler(IHubContext<ChatHub> hub, IMapper mapper)
         {
             _hub = hub;
+            _mapper = mapper;
         }
 
         public async Task Handle(MessageCreatedEvent @event)
         {
-            var streamKey = @event.StreamKey;
-            await _hub.Clients.Group(streamKey).SendAsync(SignalRMethodDefine.ReceiveMessage, @event);
+            if(@event.ChatType == Models.ChatType.PRIVATE)
+            {
+                MessageBaseDto messageBaseDto = _mapper.Map<MessageBaseDto>(_mapper.Map<Message>(@event));
+                await _hub.Clients.Users(@event.MsgRecipientId.ToString()).SendAsync("ReceiveMessage", messageBaseDto);
+            }
         }
     }
 }