unreal-engine（unreal 引擎）

Garbage Collection

• Raw pointers to UObjects get garbage collected — use UPROPERTY() to prevent
• UPROPERTY() marks for GC tracking — without it, pointer becomes dangling
• TWeakObjectPtr for optional references — doesn't prevent collection, check IsValid()
• NewObject<T>() for UObjects — never raw new, GC won't track it

UPROPERTY and UFUNCTION

• UPROPERTY() required for Blueprint access — and for GC tracking
• UFUNCTION() for Blueprint callable/events — also required for replication
• EditAnywhere vs VisibleAnywhere — edit allows changes, visible is read-only
• BlueprintReadWrite vs BlueprintReadOnly — controls Blueprint access level

Actor Lifecycle

• BeginPlay after all components initialized — safe to access components
• Constructor runs on CDO (Class Default Object) — don't spawn actors or access world
• PostInitializeComponents before BeginPlay — for component setup
• EndPlay for cleanup — called on destroy and level transition

Tick Performance

• Disable tick when not needed — PrimaryActorTick.bCanEverTick = false
• Use timers instead of tick + counter — GetWorldTimerManager().SetTimer()
• Tick groups for ordering — PrePhysics, DuringPhysics, PostPhysics
• Blueprint tick expensive — move hot logic to C++

Replication

• Server is authority — clients request, server validates and replicates
• UPROPERTY(Replicated) for variable sync — implement GetLifetimeReplicatedProps
• UFUNCTION(Server) for client-to-server RPC — must be Reliable or Unreliable
• HasAuthority() to check if server — before executing authoritative logic
• Role and RemoteRole for network role checks — ROLE_Authority is server

Asset References

• Hard references load with parent — bloats memory, use for always-needed
• Soft references (TSoftObjectPtr) load on demand — for optional or large assets
• LoadSynchronous() or AsyncLoad for soft refs — don't access until loaded
• Blueprint class references: TSubclassOf<T> — type-safe class selection

Memory and Pointers

• TSharedPtr for non-UObjects — reference counted, auto-deletes
• TUniquePtr for exclusive ownership — can't copy, moves only
• MakeShared<T>() for creation — single allocation for object and control block
• Never mix raw new/delete with smart pointers — choose one pattern

Common Mistakes

• Accessing null actor in Blueprint — use IsValid() node before access
• PIE (Play In Editor) vs packaged build differ — test shipping build
• Hot reload corrupts Blueprints — close editor, build, reopen
• GetWorld() null in constructor — world doesn't exist yet, use BeginPlay
• Spawning in constructor crashes — defer to BeginPlay or later
• FString for display, FName for identifiers — FName is hashed, faster comparison