UUnrealReactBridgeSubsystem

Source: SampleProject/Plugins/UnrealReactBridge/Source/UnrealReactBridge/Public/UnrealReactBridgeSubsystem.h

UGameInstanceSubsystem that owns the HUD-widget registry and routes events between Sender/Receiver components and the active UWebHUDWidget instances. HUD widgets self-register in NativeConstruct and unregister in NativeDestruct, so most users never touch the subsystem directly — drop a ReactBridgeSender / ReactBridgeReceiver component and the wiring is automatic.

Use the subsystem directly when you need:

• A targeted send from C++ without spawning a Sender component.
• A targeted send from a Blueprint that doesn't have a Sender on hand (e.g. Game Mode, Subsystem, REST callback).
• Diagnostics — manual broadcast during debugging.

TIP

Broadcasts that arrive before any HUD widget has registered are buffered (up to 100 entries) and flushed when the first widget registers. This means GameMode::BeginPlay initial-state pushes are safe even though the Level Blueprint creates the widget afterwards.

Get

static UUnrealReactBridgeSubsystem* Get(UWorld* World);

BlueprintCallable. Convenience accessor — resolves the owning UGameInstance from World and returns its subsystem, or nullptr if either is unavailable.

Param	Type	Required	Notes
World	UWorld*	yes	Any world reference (GetWorld(), WorldContextObject->GetWorld())

Returns — Subsystem pointer or nullptr.

BroadcastEvent

void BroadcastEvent(const FString& EventName, const FString& JsonData);

Fans the event out to every registered HUD widget in the current GameInstance.

Param	Type	Required	Notes
EventName	FString	yes	Case-sensitive event name. Matches React-side window.ue.bridge.on(name, ...) subscriptions.
JsonData	FString	yes	Valid JSON string. Pass "{}" for no payload. Reaches React as event.detail.

Returns — void.

Behavior — If no widget is registered yet, the broadcast is buffered (FIFO, capped at 100). The buffer drains the moment the first widget registers.

Example

if (auto* Sub = UUnrealReactBridgeSubsystem::Get(GetWorld()))
{
    Sub->BroadcastEvent(TEXT("game:paused"), TEXT("{\"reason\":\"menu\"}"));
}

SendEvent

void SendEvent(const FString& BridgeName, const FString& EventName, const FString& JsonData);

Targeted send — delivers only to the widget whose BridgeName matches.

Param	Type	Required	Notes
BridgeName	FString	yes	Case-sensitive. Must match UWebHUDWidget::BridgeName (or the Name of an Add Web HUD layer).
EventName	FString	yes	Case-sensitive event name.
JsonData	FString	yes	Valid JSON string; "{}" for no payload.

Returns — void.

Behavior — Silently no-ops if BridgeName does not match any registered widget. If Debug Mode is enabled in Project Settings, the miss is reported in the Output Log. Targeted sends are not buffered: deliver-or-drop.

Example

if (auto* Sub = UUnrealReactBridgeSubsystem::Get(GetWorld()))
{
    Sub->SendEvent(TEXT("HpBar"), TEXT("player:health:update"),
                   TEXT("{\"value\":75,\"max\":100}"));
}

See also

• /guide/sender-receiver — when to use components vs the subsystem
• /reference/bridge-protocol — wire format and event delivery rules