[Blazor] NullReferenceException in RenderTree and massive memory usage

[helloserve]

When I attempt to test my project end-to-end from the UI down to the SQL database and back out, I see two NullReferenceException entries in the Output window, and the Visual Studio Debug Console, and RAM usage shoots up to 25GB.

To Reproduce

Steps to reproduce the behavior:

1. Running 3.0.0-preview5.19227.x on all components and packages
2. Pull the code in this branch
3. Setup a database and apply the Vxxx__Blogs.sql script. Insert a blog entry with key title-1.
4. Fulfill appsettings.json config for connection string.
5. Run app, click on "Blogs" nav button and then on "Title 1" entry.
6. Check Output window and diagnostics pane.

The output I see is

System.NullReferenceException: Object reference not set to an instance of an object.
   at helloserve.com.Pages.Blog.BuildRenderTree(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__5_0(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.ProcessRenderQueue()
Microsoft.AspNetCore.Components.Server.ComponentHub: Warning: Unhandled Server-Side exception

System.NullReferenceException: Object reference not set to an instance of an object.
   at helloserve.com.Pages.Blog.BuildRenderTree(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__5_0(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.ProcessRenderQueue()
Microsoft.AspNetCore.Routing.EndpointMiddleware: Information: Executed endpoint '/_blazor'
Microsoft.AspNetCore.Hosting.Diagnostics: Information: Request finished in 4799.7255000000005ms 101 
'helloserve.com.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\3.0.0-preview5-27626-15\System.Diagnostics.Process.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
The thread 0x33a4 has exited with code 0 (0x0).
The thread 0x22c4 has exited with code 0 (0x0).
The program '[20408] helloserve.com.exe' has exited with code -1 (0xffffffff).

Expected behavior

When you switch the solution configuration to UITest, a compiler directive in Startup.cs swaps out a mock service for the page. This hard coded blog post entry is loaded and rendered correctly by the Blazor component.

I might be doing something wrong elsewhere in my stack, but I find it strange that I would see it manifest in the page and not earlier. The memory usage is a big concern though...

[helloserve]

So I got around the problem. In the sample FetchData.razor page there is this section:

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

If I include this in my own Blog.razor page it works, and shows the blog from the database correctly after showing the "Loading..." text. I guess I'm missing some detail on the life cycle on a Blazor page. Is there some material about this?

The RAM usage is still an issue, and makes it really hard to iterate over possible solutions.

[mkArtakMSFT]

Thanks for contacting us, @helloserve.
We've done really many changes in this area and we believe this is not reproducible any more as there are preventative measures in place for this behavior. If you still face this issue, please reopen.