Event Dispatcher: create, bind, and call with custom data

SETUP: In your BP, create an Event Dispatcher (e.g. 'OnPlayerDied') in the My Blueprint panel. BIND (in another BP): Get reference to actor → Bind Event to OnPlayerDied → connect a Custom Event as the target. CALL (in owning BP): Call OnPlayerDied (appears as a pink node) → this broadcasts to all bound listeners. Key: Event Dispatchers are called with 'Call <DispatcherName>' (not 'Broadcast'). Binding is done via 'Bind Event to <DispatcherName>' which has an 'Event' exec-like pin.

Event Dispatcher binding has wrong parameter types

Why: You're binding a function to an Event Dispatcher (Delegate), but the function's parameters don't match the dispatcher's expected signature '{expected}'. You passed '{got}'. Fix: Either: (a) change your function's input parameter types to match the dispatcher (open the function → My Blueprint → Inputs section → match types one-by-one), or (b) bind a DIFFERENT function whose signature already matches. The Details panel of the Bind Event node shows the expected signature.

Event Dispatcher

A typed broadcast — bind one or many listeners, fire once, all run. Use for loose coupling (e.g. health changed → UI update).

Event dispatcher pattern for decoupled communication between actors

Pattern: Actor A declares EventDispatcher OnScoreChanged(int NewScore). Actor B (listener) BeginPlay: GetActorOfClass(A) → BindEvent(OnScoreChanged) → custom event handler. Actor A calls OnScoreChanged.Broadcast(Score) when score changes. Bind in BeginPlay, Unbind in EndPlay to avoid dangling references.

Blueprint communication: 4 methods ranked by coupling

1. DIRECT REFERENCE (tightest coupling): Get reference → CastTo<BP_Other> → call function. Use when: actor A always knows about actor B (e.g. Player → HUD). 2. CAST via GetAllActorsOfClass (loose): find → cast → call. Use when: you need to find actors dynamically. 3. EVENT DISPATCHER (loose): Owner calls dispatcher → listeners receive event. Use when: one actor notifies many others (e.g. death notification). 4. BLUEPRINT INTERFACE (loosest): Call interface message → any implementing actor responds. Use when: multiple different actor types should respond to same action (e.g. 'Interact'). 5. GAME INSTANCE (persistent): Store shared data in GameInstance → GetGameInstance → Cast. Use when: data must survive level loads.

Delegate

A type-safe function pointer used by Event Dispatchers and bindings. Bind, broadcast, unbind.

Pickup and collectible system with overlap trigger

Pattern: Pickup actor with SphereCollision(overlap), StaticMesh visual. OnComponentBeginOverlap → CastTo PlayerCharacter → Success: call AddScore/AddItem interface on player → PlaySoundAtLocation → SpawnEmitterAtLocation → DestroyActor(self). Set collision to OverlapOnlyPawn for performance.

Spawn system with wave management for enemies

Pattern: Variables CurrentWave(int)=0, EnemiesAlive(int)=0, EnemiesPerWave(Array<int>). StartWave: CurrentWave++ → SET EnemiesAlive=EnemiesPerWave[CurrentWave]. Timer looping: Branch(SpawnedThisWave < EnemiesPerWave[CurrentWave]) → SpawnActor(EnemyClass, RandomSpawnPoint) → SpawnedThisWave++. OnEnemyDeath: EnemiesAlive-- → Branch(EnemiesAlive <= 0) → StartNextWave or Victory.

Spawn actor at location with collision handling

Pattern: Trigger → SpawnActorFromClass(Class, MakeTransform(Location, Rotation, Scale), CollisionHandling, Owner) → ReturnValue → IsValid branch → use spawned actor. Always check IsValid on ReturnValue. For many spawns, spread across frames with timer to avoid hitches.

Possess — make a Controller possess a Pawn