事件处理(Handling Events)和委托（Delegate）代码示例（一）【UE4】【C++】

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 values
      AMyTriggerVolume::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; ///< 每帧都调用 Tick()
      	TriggerZone = CreateDefaultSubobject<UBoxComponent>("TriggerZone");
      	TriggerZone->SetBoxExtent(FVector(200, 200, 100));// 设置触发区域的范围
      }
      // Called when the game starts or when spawned
      void AMyTriggerVolume::BeginPlay()
      {
      	Super::BeginPlay();
      }
      // Called every frame
      void 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。
（效果为 当玩家进入触发区域，点光源亮）

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

DECLARE_DELEGATE(FStandardDelegateSignature)
 

然后，为 UE4TestGameMode 类添加一个新成员

FStandardDelegateSignature MyStandardDelegate;
 

接着，我们新建一个 Actor 子类——DelegateListener，主要实现具体方法，以及负责委托的绑定和解绑

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 values
      ADelegateListener::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<UPointLightComponent>("PointLight");
      	RootComponent = PointLight;
      	PointLight->SetVisibility(false);
      }
      // Called when the game starts or when spawned
      void ADelegateListener::BeginPlay()
      {
      	Super::BeginPlay();
      	UWorld* TheWorld = GetWorld();
     	if (TheWorld != nullptr)
      	{
      		AGameMode* GameMode = Cast<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
      		AUE4TestGameMode * MyGameMode = Cast<AUE4TestkGameMode>(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);// 其实就是绑定了 EnableLight 函数指针。
              }
      	}
      }
      // Called every frame
      void 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<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
      		AUE4TestGameMode * MyGameMode = Cast<AUE4TestGameMode>(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<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
      		AUE4TestGameMode * MyGameMode = Cast<AUE4TestGameMode>(GameMode);
     		// ❤ 执行委托的函数
      		MyGameMode->MyStandardDelegate.ExecuteIfBound();
      	}
  
 

（未完待续）
 

文章来源: panda1234lee.blog.csdn.net，作者：panda1234lee，版权归原作者所有，如需转载，请联系作者。

原文链接：panda1234lee.blog.csdn.net/article/details/63834770