UE5 委托与代理完全指南

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// 声明一个返回bool、接受int参数的委托
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DECLARE_DELEGATE_RetVal_OneParam(bool, FOnPlayerAction, int32)
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// 或者使用宏自动生成
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DECLARE_MULTICAST_DELEGATE_OneParam(FOnDamageDelegate, float)

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// 无参数
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DECLARE_DELEGATE(FSimpleDelegate)
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// 单参数（最多8个）
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DECLARE_DELEGATE_OneParam(FOneParamDelegate, int32)
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DECLARE_DELEGATE_TwoParams(FTwoParamDelegate, int32, FString)
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DECLARE_DELEGATE_ThreeParams(FThreeParamDelegate, AActor*, float, FVector)
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// 返回值
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DECLARE_DELEGATE_RetVal(bool, FReturnBoolDelegate)
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DECLARE_DELEGATE_RetVal_OneParam(int32, FReturnIntDelegate, float)

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class AMyActor : public AActor
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{
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    UFUNCTION()
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    void HandleDamage(float Damage);
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    void BindDelegate();
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};
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void AMyActor::BindDelegate()
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{
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    // 假设有一个委托对象
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    FOnDamageDelegate OnDamage;
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    // 绑定到成员函数
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    OnDamage.AddDynamic(this, &AMyActor::HandleDamage);
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}

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void MyStaticFunction(float Damage)
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{
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    UE_LOG(LogTemp, Warning, TEXT("Static handler: %f"), Damage);
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}
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void AMyActor::BindStatic()
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{
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    FOnDamageDelegate OnDamage;
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    OnDamage.AddStatic(&MyStaticFunction);
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}

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void AMyActor::BindLambda()
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{
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    FOnDamageDelegate OnDamage;
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    // C++14+ 支持Lambda
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    int32 Count = 0;
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    OnDamage.AddLambda([this, Count](float Damage) {
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        UE_LOG(LogTemp, Warning, TEXT("Lambda: %f, Count: %d"), Damage, Count);
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    });
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}

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// 声明多播委托
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DECLARE_MULTICAST_DELEGATE_TwoParams(FOnHealthChanged, float /*OldHealth*/, float /*NewHealth*/);
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// 在类中定义
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UPROPERTY()
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FOnHealthChanged OnHealthChangedDelegate;
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// 广播（调用所有绑定的函数）
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void AMyCharacter::TakeDamage(float Damage)
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{
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    float OldHealth = Health;
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    Health -= Damage;
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    OnHealthChangedDelegate.Broadcast(OldHealth, Health);
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}

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void AMyActor::RegisterCallbacks(AMyCharacter* Character)
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{
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    if (Character)
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    {
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        // 添加监听
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        Character->OnHealthChangedDelegate.AddDynamic(this, &AMyActor::OnHealthChanged);
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        // 移除监听
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        Character->OnHealthChangedDelegate.RemoveDynamic(this, &AMyActor::OnHealthChanged);
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    }
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}
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void AMyActor::OnHealthChanged(float OldHealth, float NewHealth)
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{
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    UE_LOG(LogTemp, Warning, TEXT("Health: %f -> %f"), OldHealth, NewHealth);
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}

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// 清空所有监听
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OnHealthChangedDelegate.Clear();

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// 用于蓝图支持的动态委托
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DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(FOnSpellCast, FVector, Location, float, Damage);
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// 实现
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UPROPERTY(BlueprintAssignable)
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FOnSpellCast OnSpellCastDelegate;
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// 在Blueprint中绑定

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// UGameInstanceSubsystem 实现全局事件
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UCLASS()
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class UEventManager : public UGameInstanceSubsystem, public FTickableGameObject
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{
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    GENERATED_BODY()
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public:
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    // 玩家相关事件
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    FDelegateHandle OnPlayerDamagedHandle;
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    FDelegateHandle OnPlayerDiedHandle;
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    virtual void Initialize(FSubsystemCollectionBase& Collection) override;
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    virtual void Deinitialize() override;
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    // 事件广播
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    void BroadcastPlayerDamaged(AActor* Player, float Damage);
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    void BroadcastPlayerDied(AActor* Player);
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    // 事件监听
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    void ListenPlayerDamaged(UObject* Listener, FName FunctionName);
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};

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void UEventManager::Initialize(FSubsystemCollectionBase& Collection)
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{
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    Super::Initialize(Collection);
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}
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void UEventManager::BroadcastPlayerDamaged(AActor* Player, float Damage)
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{
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    // 广播到所有监听者
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    OnPlayerDamaged.Broadcast(Player, Damage);
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}
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void UEventManager::ListenPlayerDamaged(UObject* Listener, FName FunctionName)
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{
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    if (Listener && !FunctionName.IsNone())
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    {
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        FScriptDelegate Delegate;
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        Delegate.BindUFunction(Listener, FunctionName);
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        OnPlayerDamaged.Add(Delegate);
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    }
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}