Interface: implement and call Blueprint interface function

SETUP: Create a Blueprint Interface asset (BPI_Interactable) with a function 'Interact'. IMPLEMENT: In the actor BP, go to Class Settings → Interfaces → Add → BPI_Interactable. Then implement the 'Interact' event that appears in the event graph. CALL: Get actor reference → 'Does Implement Interface(BPI_Interactable)' → Branch → True → 'Interact (Message)' node (the interface call). Key: Interface calls are 'Message' type nodes. Use 'Does Implement Interface' before calling to avoid crashes on actors that don't implement it.

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.

Blueprint graph is too large — UE5 refuses to compile

Why: UE5 has a soft limit on graph complexity (typically ~2000 nodes per function). Your Blueprint exceeded it. Fix: Split logic across multiple functions: pick a logically-cohesive section, right-click → Collapse to Function. Repeat until each function is under ~500 nodes. Consider creating separate Macro Library or Blueprint Function Library assets to share common chunks.

Widget Blueprint

A UMG (Unreal Motion Graphics) UI Blueprint. Holds the visual hierarchy + the logic graph for menus, HUDs, and panels.

Asset reference points to a Blueprint that no longer exists

Why: Some node or variable hardcoded a reference to BP_{name}, but that file was deleted or moved. The Asset Registry can't resolve it. Fix: Either: (a) re-create BP_{name} if accidentally deleted (Content Browser → right-click → Blueprint Class), or (b) update the reference to point at the correct existing Blueprint, or (c) make the reference soft (TSoftObjectPtr) so missing assets don't fail compilation.

Create a Blueprint for a simple elevator that moves between two floors when a button is pressed

Common Blueprint mistakes and how to fix them

MISTAKE 1: Calling GetAllActorsOfClass every Tick. FIX: Cache results in BeginPlay or use delegates/tags instead. MISTAKE 2: Not checking IsValid before using object references. FIX: Always IsValid → Branch → Is Valid before dereferencing. MISTAKE 3: Using hard references to large assets in variables. FIX: Use Soft Object References + AsyncLoadAsset. MISTAKE 4: Tick enabled on many actors doing heavy work. FIX: SetActorTickInterval(0.1) for non-critical logic, or use Timers. MISTAKE 5: Casting to specific class without checking IsValid first. FIX: CastTo has 'Cast Failed' output — always handle it. MISTAKE 6: Modifying array elements by getting then setting a copy. FIX: Use 'Array Set' with index to modify in-place. MISTAKE 7: Creating widget every time it's shown. FIX: Create once → cache reference → show/hide with SetVisibility or Add/RemoveFromParent.

Performance optimization checklist for Blueprints

1. TICK MANAGEMENT: - Disable tick on static actors (SetActorTickEnabled=false). - Use SetActorTickInterval(0.1-0.5) for AI, non-critical systems. - Prefer event-driven over tick polling where possible. 2. AVOID EVERY-TICK EXPENSIVE CALLS: - GetAllActorsOfClass: cache in BeginPlay, refresh only when needed. - CastTo: cache result in variable after first cast. - GetComponentByClass: call once and store reference. 3. VISIBILITY: - SetActorHiddenInGame + SetActorTickEnabled=false for off-screen actors. - Use LOD (Level of Detail) on meshes. 4. SPAWNING: - Use object pooling for frequently spawned/destroyed actors (bullets, effects). 5. EVENTS OVER POLLING: - Use overlap events instead of periodic distance checks. - Use delegates/dispatchers instead of checking conditions each frame.

Create a Blueprint for a simple FPS weapon that shoots raycasts and deals damage

Create a Blueprint Actor that plays a sound and spawns a particle effect at its location when destroyed