blazor-layout-issue

Link to the public bug report: dotnet/aspnetcore#50724

Describe the bug

When a Blazor component is used in MainLayout.razor in a Blazor app with Blazor Server interactive render mode, passing this component as a cascading parameter results in the component having the value null.

Details

Note: The explanations below are extracted from the code we are using, which is proprietary. This is why the scenario is a bit simplified and might look like the functionality can be achieved in a different way, but please focus on how a component passed as a cascading parameter in MainLayout.razor becomes null - this is the main issue we are facing. I am not able to directly show the real code as it is licensed.

The Blazor app renders a RootComponent, which basically re-renders its child content. The component wraps the @Body element inside MainLayout.razor and it is used together with a ContentComponent that appears on the Home.razor page.

When the app is run, the first time the ContentComponent is initialized, the RootComponent has its correct value, but on consecutive calls it becomes null.

Expected Behavior

The component that is passed down the hierarchy as a cascading parameter should not be null.

Note 1: The problem is not reproducible when exactly the same configuration is used in a .NET 6.0 project, so I suppose this is related to the new interactive modes and how they work. Please advise if some configuration is incorrect, but for now, this seems like a regression to us.

Note 2: We do not want to multi-target in order to "workaround" this in some why (if you can suggest a workaround) as we want to avoid this following the suggestion in https://learn.microsoft.com/en-au/aspnet/core/blazor/components/render-modes?view=aspnetcore-8.0#apply-a-render-mode-to-a-component-definition - "Component authors should avoid coupling a component's implementation to a specific render mode"

Note 3: The code works if the RootComponent is moved to wrap the whole Home.razor page, but this is not an option for us - we want to keep the compatibility of the configuration in MainLayout.razor.

Steps To Reproduce

1. Clone https://github.com/Stamo-Gochev/blazor-layout-issue
2. Run the app and open the Home.razor page
3. Observe the log for the error or set a breakpoint in ContentComponent and see the Debug window when the RootComponent value becomes null or see the attached GIF

Exceptions (if any)

The cascading value is null.

.NET Version

8.0.100-rc.1.23455.8

Anything else?

$ dotnet --info
.NET SDK:
 Version:   8.0.100-rc.1.23455.8
 Commit:    e14caf947f

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19044
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.100-rc.1.23455.8\

.NET workloads installed:
There are no installed workloads to display.

Host:
  Version:      8.0.0-rc.1.23419.4
  Architecture: x64
  Commit:       92959931a3
  RID:          win-x64

.NET SDKs installed:
  8.0.100-rc.1.23455.8 [C:\Program Files\dotnet\sdk]