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1. 通过重写虚函数来处理事件

MyTriggerVolume.h

#pragma once#include "GameFramework/Actor.h"#include "MyTriggerVolume.generated.h"UCLASS()class TEST_API AMyTriggerVolume : public AActor{	GENERATED_BODY()	public:		// Sets default values for this actor's properties	AMyTriggerVolume();	// Called when the game starts or when spawned	virtual void BeginPlay() override;		// Called every frame	virtual void Tick( float DeltaSeconds ) override;	UPROPERTY()	UBoxComponent* TriggerZone;		UFUNCTION()	virtual void NotifyActorBeginOverlap(AActor* OtherActor) override;	UFUNCTION()	virtual void NotifyActorEndOverlap(AActor* OtherActor) override;};

MyTriggerVolume.cpp

#include "Test.h"#include "UE4TestGameMode.h"#include "MyTriggerVolume.h"// Sets default valuesAMyTriggerVolume::AMyTriggerVolume(){ 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.	PrimaryActorTick.bCanEverTick = true;	TriggerZone = CreateDefaultSubobject
   
    ("TriggerZone");	TriggerZone->SetBoxExtent(FVector(200, 200, 100));// 设置触发区域的范围}// Called when the game starts or when spawnedvoid AMyTriggerVolume::BeginPlay(){	Super::BeginPlay();	}// Called every framevoid AMyTriggerVolume::Tick( float DeltaTime ){	Super::Tick( DeltaTime );}// 重写虚函数来响应事件void AMyTriggerVolume::NotifyActorBeginOverlap(AActor* OtherActor){	GEngine->AddOnScreenDebugMessage(-1, 1, FColor::Red, FString::Printf(TEXT("%s entered me"), *(OtherActor->GetName())));// 注意FString::Format需要解引用}// 重写虚函数来响应事件void AMyTriggerVolume::NotifyActorEndOverlap(AActor* OtherActor){	GEngine->AddOnScreenDebugMessage(-1, 1, FColor::Red, FString::Printf(TEXT("%s left me"), *(OtherActor->GetName())));}
   

2. 绑定在 UFUNCTION 函数上的委托（不带参数）

委托的好处在于，我们不用知道当前指派的函数的细节就可以调用它，它是一种安全版本的函数指针。

以下代码将展示如何关联 UFUNCTION 到一个委托上，即委托执行时，UFUNCTION 将被调用。

首先在 UE4TestGameMode.h 中添加一个委托声明（在 UCLASS 之前），如下：

DECLARE_DELEGATE(FStandardDelegateSignature)

FStandardDelegateSignature MyStandardDelegate;

DelegateListener.h

UCLASS()class TEST_API ADelegateListener : public AActor{	GENERATED_BODY()	public:		// Sets default values for this actor's properties	ADelegateListener();	// Called when the game starts or when spawned	virtual void BeginPlay() override;		// Called every frame	virtual void Tick( float DeltaSeconds ) override;		UFUNCTION()	void EnableLight();	UFUNCTION()	virtual void EndPlay(const EEndPlayReason::Type EndPlayReason) override;	UPROPERTY()	UPointLightComponent* PointLight;	};

DelegateListener.cpp

#include "Test.h"#include "UE4TestGameMode.h" // 注意 include 的位置#include "DelegateListener.h"// Sets default valuesADelegateListener::ADelegateListener(){ 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.	PrimaryActorTick.bCanEverTick = true;	PointLight = CreateDefaultSubobject
   
    ("PointLight");	RootComponent = PointLight;		PointLight->SetVisibility(false);}// Called when the game starts or when spawnedvoid ADelegateListener::BeginPlay(){	Super::BeginPlay();	UWorld* TheWorld = GetWorld();	if (TheWorld != nullptr)	{		AGameMode* GameMode = Cast
    
     (UGameplayStatics::GetGameMode(TheWorld));		AUE4TestGameMode * MyGameMode = Cast
     
      (GameMode);		if (MyGameMode != nullptr)		{			// ❤ 绑定一个基于 UObject 的成员函数的委托。UObject 委托保留了一个弱引用在你的对象上，可以通过.ExecuteIfBound() 来调用委托的函数			MyGameMode->MyStandardDelegate.BindUObject(this, &ADelegateListener::EnableLight);// 其实就是将 EnableLight 函数绑定在了委托上。                 }	}}// Called every framevoid ADelegateListener::Tick( float DeltaTime ){	Super::Tick( DeltaTime );}void ADelegateListener::EnableLight(){	PointLight->SetVisibility(true);}void ADelegateListener::EndPlay(const EEndPlayReason::Type EndPlayReason){	Super::EndPlay(EndPlayReason);	UWorld* TheWorld = GetWorld();	if (TheWorld != nullptr)	{		AGameMode* GameMode = Cast
      
       (UGameplayStatics::GetGameMode(TheWorld));		AUE4TestGameMode * MyGameMode = Cast
       
        (GameMode);		if (MyGameMode != nullptr)		{			// 解绑委托			MyGameMode->MyStandardDelegate.Unbind();		}	}}
       
      
     
    
   

值得注意的是，如果我们绑定的是普通的C++函数，那么就应该将 BindUObject 改为 BindRaw，如果是静态方法，那就改为 BindStatic。

最后，回到我们之前的 MyTriggerVolume.cpp， 利用 GameMode（我们之前声明委托和定义委托成员的地方） 执行委托，

在 NotifyActorBeginOverlap 方法中添加以下代码：

UWorld* TheWorld = GetWorld();	if (TheWorld != nullptr)	{		AGameMode* GameMode = Cast
   
    (UGameplayStatics::GetGameMode(TheWorld));		AUE4TestGameMode * MyGameMode = Cast
    
     (GameMode);		// ❤ 执行委托的函数		MyGameMode->MyStandardDelegate.ExecuteIfBound();	}
    
   

（未完待续）

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