[UE4]事件处理(Handling Events)和委托（Delegate）代码示例（一）-白红宇

[UE4]事件处理(Handling Events)和委托（Delegate）代码示例（一）

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发布时间：2019-06-12

本文共 5404 字，大约阅读时间需要 18 分钟。

1. 通过重写虚函数来处理事件

MyTriggerVolume.h

自定义一个Actor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;      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 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 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
      
       ("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
       
        (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 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
         
          (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();  }

转载于:https://www.cnblogs.com/timy/p/8682719.html

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