Page navigation does not honour ASYNC OnInitializedAsync design pattern RSS

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  graeme.thoms...

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  Page navigation does not honour ASYNC OnInitializedAsync design pattern

  Apr 29, 2020 06:07 AM|graeme.thomson@avaxa.com|LINK

  I have built a server-side BLAZOR app based upon the sample project from Visual Studio 2019 Preview.
  I have a menu item that navigates to my page using Navlink as:
           <NavLink class="nav-link" href="StudentsExposedToStudents">
                      <span class="oi oi-list-rich" aria-hidden="true"></span> Students / Students
           </NavLink>

  The target page uses the design pattern from the sample and attempts to show a message whilst waiting for data as:
           @if (intersections == null)   { <p><em>Loading...</em></p> }
  
  Typically the database service takes about 15 seconds to provide the data using an ASYNC method, but the advisory text "Loading..." is never presented.
  What am I doing wrong?

  This is my page
  ----------------------------------------------------------------

  @page "/StudentsExposedToStudents"

  @using StrataDataAccess
  @inject StrataService StrataService

  <h1>List of students potentially exposed to infectious students</h1>

  @if (intersections == null)  { <p><em>Loading...</em></p> }

  else
  {
  <table class="table">
  <thead>
  <tr>
  <th> Exposed Student </th>
  <th> Contact Student Name </th>
  <th> Session Date </th>
  <th> Start Time </th>
  <th> End Time </th>
  <th> Timetable Group </th>
  <th> Exposed Hours </th>
  <th> </th>
  </tr>
  </thead>
  <tbody>
  @foreach (var item in intersections)
  {
  <tr>
  <td> @item.StudentName </td>
  <td> @item.ContactName </td>
  <td> @item.SessionStart.ToString("dd-MMM-yyyy") </td>
  <td> @item.SessionStart.ToString("H:mm") </td>
  <td> @item.SessionEnd.ToString("H:mm") </td>
  <td> @item.TimetableGroupName </td>
  <td> @item.ExposureHours.ToString("0.##") </td>
  </tr>
  }
  </tbody>
  </table>
  }

  @code {
  public IEnumerable<StrataDataAccess.StudentsExposedToStudents>
  intersections = null;

  protected override async Task OnInitializedAsync()
  {
  intersections = null;
  intersections = await StrataService.GetListOfStudentStudentIntersectionsAsync();
  intersections = intersections.OrderBy(s => s.StudentName)
  .ThenBy(s => s.ContactName);
  }
  }

  ----------------------------------------------------------------