1. 通过重写虚函数来处理事件
MyTriggerVolume.h
自定义一个继承自 Actor 的子类，添加一个 Box 组件作为触发区域，然后通过重写虚函数—— NotifyActorBeginOverlap, NotifyActorEndOverlap 来响应事件
#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）
