Blazor - OnAfterRenderAsync being fired during PreRendering and then again later

[iguanaware]

Related to #11876 (8 3.0.100-preview8-013656) It's not calling the methods twice on "a" component. It actually creates two components that each have their events fired. But the prerender one fails to get dotnet references.

Remove Html.RenderStaticComponentAsync and the problem goes away.

The bigger problem is that OnAfterRenderAsync is firing on the prerendering pass

Reproduce:

dotnet new blazorserver

add to Index.razor

@code{
    protected override async Task OnAfterRenderAsync()
    {
        Console.WriteLine($"\n\n\n{this.GetHashCode()} OnAfterRenderAsync\n\n\n");
    }
}

Below is the output (OnAfterRenderAsync

there appears twice)

info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using 'C:\Users\brian.freeman\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: https://localhost:5001
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]
      Content root path: C:\temp\bl2
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
      Executing endpoint '/_Host'
info: Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker[3]
      Route matched with {page = "/_Host"}. Executing page /_Host
info: Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker[103]
      Executing an implicit handler method - ModelState is Valid
info: Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker[104]
      Executed an implicit handler method, returned result Microsoft.AspNetCore.Mvc.RazorPages.PageResult.

8022616 OnAfterRenderAsync

info: Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker[4]
      Executed page /_Host in 79.12660000000001ms
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
      Executed endpoint '/_Host'
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/_framework/blazor.server.js
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/css/site.css
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/css/bootstrap/bootstrap.min.css
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 157.24380000000002ms 200 text/html; charset=utf-8
info: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[6]
      The file /css/site.css was not modified
info: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[6]
      The file /css/bootstrap/bootstrap.min.css was not modified
info: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[6]
      The file /_framework/blazor.server.js was not modified
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 20.921400000000002ms 304 application/javascript
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 20.9268ms 304 text/css
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 20.921300000000002ms 304 text/css
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/css/open-iconic/font/css/open-iconic-bootstrap.min.css
info: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[6]
      The file /css/open-iconic/font/css/open-iconic-bootstrap.min.css was not modified
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 2.8323ms 304 text/css
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 POST https://localhost:5001/_blazor/negotiate text/plain;charset=UTF-8 0
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
      Executing endpoint '/_blazor/negotiate'
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 GET https://localhost:5001/css/open-iconic/font/fonts/open-iconic.woff
info: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[6]
      The file /css/open-iconic/font/fonts/open-iconic.woff was not modified
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 3.7439ms 304 application/font-woff
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
      Executed endpoint '/_blazor/negotiate'
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
      Request finished in 17.8213ms 200 application/json
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/1.1 GET https://localhost:5001/_blazor?id=CXvsYbAyoczAw8Ab0QVyEw
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
      Executing endpoint '/_blazor'
info: Microsoft.AspNetCore.SignalR.HubConnectionContext[1]
      Completed connection handshake. Using HubProtocol 'blazorpack'.

65357506 OnAfterRenderAsync

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview8-013656
 Commit:    8bf06ffc8d

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview8-013656\

Host (useful for support):
  Version: 3.0.0-preview8-28405-07
  Commit:  d01b2fb7bc

.NET Core SDKs installed:
  2.1.507 [C:\Program Files\dotnet\sdk]
  2.1.508 [C:\Program Files\dotnet\sdk]
  2.1.701 [C:\Program Files\dotnet\sdk]
  2.1.800-preview-009677 [C:\Program Files\dotnet\sdk]
  2.1.800-preview-009696 [C:\Program Files\dotnet\sdk]
  2.1.800 [C:\Program Files\dotnet\sdk]
  2.1.801 [C:\Program Files\dotnet\sdk]
  2.2.301 [C:\Program Files\dotnet\sdk]
  2.2.400 [C:\Program Files\dotnet\sdk]
  3.0.100-preview7-012821 [C:\Program Files\dotnet\sdk]
  3.0.100-preview8-013656 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview7.19365.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview8.19405.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview7-27912-14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview8-28405-07 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview7-27912-14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview8-28405-07 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

[mkArtakMSFT]

Thanks for contacting us, @iguanaware. In Preview8 pre-rendering is a separate render than the actual rendering. So that's expected. In Preview 9 we don't run the OnAfterRenderAsync as part of pre-rendering.

[schmitch]

@mkArtakMSFT I think this design should be looked at again. currently when somebody wants to use pre-rendering and makes some database calls or http calls that won't be cheap, it will be really painful.

I'm also pretty sure that there is no need to actually call initalization logic twice. I mean react does not need it, neither does angular.

This "by design" thing will have a huge impact for users that want to improve some razor pages with interactive blazor components. I know it's probably not easy to support, but at least it should've been put to the backlog/discussed instead of closed as "by design".