UE5 C++ Delegates & Events

UE5 C++ Delegates & Events

Delegates provide type-safe callbacks for event-driven programming in Unreal Engine.

Delegate Types

Type	Blueprint	Multiple Bindings	Use Case
Single	No	No	Internal C++ callbacks
Multicast	No	Yes	C++ event broadcasting
Dynamic Single	Yes	No	Single Blueprint callback
Dynamic Multicast	Yes	Yes	Blueprint event dispatchers

Declaration Macros

// Single-cast (C++ only)
DECLARE_DELEGATE(FOnSimpleEvent);
DECLARE_DELEGATE_OneParam(FOnHealthChanged, float);
DECLARE_DELEGATE_TwoParams(FOnDamage, float, AActor*);
DECLARE_DELEGATE_RetVal(bool, FOnValidate);

// Multicast (C++ only)
DECLARE_MULTICAST_DELEGATE(FOnSimpleMulticast);
DECLARE_MULTICAST_DELEGATE_OneParam(FOnScoreChanged, int32);

// Dynamic (Blueprint compatible)
DECLARE_DYNAMIC_DELEGATE(FOnDynamicSimple);
DECLARE_DYNAMIC_MULTICAST_DELEGATE(FOnDeathSignature);
DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FOnHealthChangedSignature, float, NewHealth);
DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(FOnDamageSignature, float, Damage, AActor*, Instigator);

Naming Convention

• F prefix for delegate type: FOnScoreChangedSignature
• Signature suffix for type declaration
• On prefix for event names

Blueprint-Exposed Events

// In header - declare delegate type
DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FOnHealthChangedSignature, float, NewHealth);

UCLASS()
class UHealthComponent : public UActorComponent
{
    GENERATED_BODY()

public:
    // BlueprintAssignable exposes to Blueprint Event Graph
    UPROPERTY(BlueprintAssignable, Category = "Events")
    FOnHealthChangedSignature OnHealthChanged;

    void TakeDamage(float Amount)
    {
        CurrentHealth -= Amount;
        OnHealthChanged.Broadcast(CurrentHealth);  // Notify all listeners
    }
};

Binding Patterns

// C++ binding
MyDelegate.BindUObject(this, &UMyClass::HandleEvent);
MyMulticast.AddUObject(this, &UMyClass::HandleEvent);

// Lambda binding
MyDelegate.BindLambda([](float Value) { /* ... */ });

// Dynamic binding (Blueprint compatible)
MyDynamicDelegate.AddDynamic(this, &UMyClass::HandleEvent);
MyDynamicDelegate.AddUniqueDynamic(this, &UMyClass::HandleEvent);  // Prevents duplicates

Best Practices

Practice	Reason
Use AddUniqueDynamic	Prevents duplicate subscriptions
Wrap complex data in USTRUCT	Blueprint compatibility
Use Multicast for events	Single-cast Events are deprecated
Sparse delegates for rare events	Memory optimization
Check IsBound() before ExecuteIfBound()	Avoid crashes

Unbinding

// Always unbind in destructor or when no longer needed
MyDelegate.Unbind();
MyMulticast.RemoveAll(this);
MyDynamicDelegate.RemoveDynamic(this, &UMyClass::HandleEvent);

Documentation: https://dev.epicgames.com/documentation/en-us/unreal-engine/delegates-and-lamba-functions-in-unreal-engine