Critical Bug: Blazor Server – SignalR NullReferenceException when closing modal and updating QuickGrid #62858
Description
📋 Description
In a Blazor Server app, when a modal component is closed (via @if) and an EventCallback adds an item to a list bound to a QuickGrid, the server crashes with a NullReferenceException in SignalR.
This causes:
- The entire app to freeze
- The SignalR circuit to die silently
- No exception being caught by any
ErrorBoundary
🧪 Repro steps
- A parent component displays a
QuickGridbound to a list:List<InvoiceDetailsModel> - A modal component is shown via
@if (IsModalVisible) - On form submit inside the modal, an
EventCallbackadds an item to the list and sets IsModalVisible = false - This causes Blazor to:
- Dispose the modal component
- Re-render the
QuickGrid
- At this point, SignalR crashes with a NullReferenceException
💣 What actually happens
RemoteJSRuntime.EndInvokeDotNet(...)throwsNullReferenceException- The app freezes completely
- No exception bubbles up
- Reproducible 100% of the time
✅ What has been tried (and failed)
| Attempted Fix | Outcome |
|---|---|
| Using @key to force modal recreation | ❌ No effect |
| Implementing IDisposable and detaching event handlers | ✅ Called, no leak — but still crashes |
| Wrapping EventCallback in InvokeAsync() or Task.Yield() | ❌ Still crashes |
| Resetting bound model before disposal (Detail = new()) | ❌ Still crashes |
| Toggling visibility (Visible=true/false) instead of @if | ❌ Same behavior |
| Delaying updates to parent via Task.Delay() | ❌ Still crashes |
| Removing QuickGrid temporarily | ✅ Prevents crash → likely trigger is grid rerender |
📎 Stack trace
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Components.Server.Circuits.RemoteJSRuntime.EndInvokeDotNet(DotNetInvocationInfo invocationInfo, DotNetInvocationResult& invocationResult)
at Microsoft.AspNetCore.SignalR.ClientProxyExtensions.SendCoreAsync(...) // decompiled source
🧰 Environment
- .NET 8.0.x
- Blazor Server
- Microsoft.AspNetCore.SignalR.Core (latest)
- Microsoft.AspNetCore.Components.QuickGrid (stable)
🙏 Request
- Can this be addressed in QuickGrid's rendering logic or the framework’s circuit lifecycle?
- At minimum, can the runtime guard against this crash instead of throwing from SendCoreAsync()?
- Should there be documentation or pattern warnings around updating QuickGrid during component disposal?