c# - Blazor - 比较上一个和下一个状态

Question

我在 Blazor 中有一个来自 api 的学生表，我还收到推送数据以更新学生信息，这基本上是数据库更改时的分数，推送工作正常，分数为正在更新，但我还想将表中已更新的字段的背景颜色更改为红色，仅将 td 标记更改几秒钟，我的代码如下:

@foreach(var student in SS.GetStudents()){
     <tr>
          <td> student.name </>
          <td> student.section </>
          // trying to compare between the previous and next state
          var stud = SS.GetStuentsCopy().SingleOrDefault(s =>s.Id == student.Id);
          var color = "";
          if(stud.score != student.score){
            color = red;
           }
          <td class="@color"> student.score </>
     </tr>
  }

   @code{
         [Inject]
         public StudentsStates SS { get; set;}
         public StudentsResponse Students { get; set; }
         protected override async Task OnInitializedAsync()
         { 
              // Subscribe to the StateChanged EventHandler
               SS.StateChanged +=
               SSAdvancedStateChanged;

          Students = await Service.GetStudents();
         // update the students and the copy together
          SS.UpdateStudents(Students)
          SS.UpdateStudentsCopy(Students)


       //upon receiving students updated score
                hubConnection = new HubConnectionBuilder()
        .WithUrl(NavigationManager.ToAbsoluteUri("/studhub"))
        .Build();

        hubConnection.On<StudentsResponse>("ReceiveMessage", s =>
        {
            // update the students after 3 sec update the copy
            SS.UpdateStudents(s);


           //Here the state is not being updated
           // unless there is a new push 
           // or the issue might be in rendering
           // FYI without the sleep also I can see the changes in the color
            System.Threading.Thread.Sleep(3000);
            SS.UpdateStudentsCopy(s);

        }

      }}

学生状态.cs

namespace Ctrl.Web.Data
{
    public class StudentsStates
    {

        public StudentsResponse Students { get; set; }
        public StudentsResponse StudentsCopy { get; set; }
        public StudentsResponse GetStudents(){return Students;}
        public StudentsResponse GetStudentsCopy(){return StudentsCopy;}
        public void UpdateStudents(Students students){ Students = students;}
        public void UpdateStudentsCopy(Students students){ StudentsCopy = students;}

}}

正如我上面所说的，一切正常，除非在一秒钟内进行多次推送，第一个推送的学生分数的背景颜色更改得太快，有时您甚至不会注意到它，因为推送的数据和状态正在更新，我想要的是在不影响下一个推送的学生分数的情况下减慢背景颜色，或者如果有更好的方法来解决这种情况，我们非常感谢您的回答。

Answer 1

我建议为学生行创建一个组件，如下所示:

@foreach(var student in SS.GetStudents())
{
      <StudentRow Student={student} />
}

然后在 StudentRow 组件中，您可以创建一个新的私有(private)学生变量，您可以在延迟 3 秒后更新它并在那里进行比较，而不是将 id 保存在列表或另一个副本中:

StudentRow.razor

  <tr>
      <td> Student.name </>
      <td> Student.section </>
      var color = "";
      if(StudentCopy.score != Student.score){
        color = red;
       }
      <td class="@color"> student.score </>
 </tr>
 @code{
         public StudentResponse StudentCopy { get; set; }
         [Parameter]
         public StudentResponse Student { get; set; }

         protected override async Task OnParametersSetAsync()
         {
          await Task.Delay(3000);
          StudentCopy = Student;

         }
      }

OnParametersSetAsync 方法在组件从渲染树中的父级接收参数时调用，并且传入的值已分配给属性。 Read more here