类型转换快速入门指南

Overview

Casting Blueprint classes is a common communication type, in which you use a reference to an Actor class Blueprint and convert it to a different class. If this conversion is successful, then you can use Direct Blueprint communication to access its information and functionality.

This method requires a reference to the Actor class Blueprint in your Level so you can use the Cast node to try to convert it to a specific class. This communication type uses a one-to-one relationship between your working Actor class Blueprint to your target Actor class Blueprint.

In this Quick Start guide, you will learn how to create an Actor in C++, that has the Blueprint casting functionality used to access information from a target Blueprint.

Setup

1. Begin by creating a new Games > Third Person > C++ project named BPCommunication.

   

Creating a Rotating Actor

For this example, you will create an Actor class Blueprint that has the functionality to rotate its Static Mesh Component when the player is nearby.

1. From the C++ Class Wizard, create a new Actor class named RotatingActor.

   

2. In the class defaults of your RotatingActor.h implement the following code.

   C++

   public:
   		
               void SetbCanRotate(bool value);
   		
           protected:
   		
               // Called when the game starts or when spawned
               virtual void BeginPlay() override;
               void RotateActor();
               bool bCanRotate;
   
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3. Navigate to your RotatingActor.cpp and declare the following code in the constructor ARotatingActor::ARotatingActor

   C++

   ARotatingActor::ARotatingActor()
        {
            RootComponent = CreateDefaultSubobject<USceneComponent>(TEXT("SceneComponent"));
            MeshComp = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("StaticMesh"));
            MeshComp->SetupAttachment(RootComponent, FAttachmentTransformRules::KeepRelativeTransform);
            bCanRotate = false;
        }

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4. Implement the following code for your ARotatingActor::RotateActor method.

   C++

   void ARotatingActor::RotateActor()
        {
            AddActorLocalRotation(ActorRotation);
        }

   Copy full snippet(4 lines long)

5. Navigate to the ARotatingActor::Tick method and implement the following code.

   C++

   void ARotatingActor::Tick(float DeltaTime)
            {
                Super::Tick(DeltaTime);
   		
                if (bCanRotate)
                {
                    RotateActor();
                }
            }

   Copy full snippet(9 lines long)

Finished Code

RotatingActor.h

#pragma once
	#include "CoreMinimal.h"
	#include "GameFramework/Actor.h"
	#include "RotatingActor.generated.h"

	UCLASS()
	class BPCOMMUNICATION_API ARotatingActor : public AActor
	{
	GENERATED_BODY()

RotatingActor.cpp

#include "RotatingActor.h"

	// Sets default values
	ARotatingActor::ARotatingActor()
	{
		// 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;
		RootComponent = CreateDefaultSubobject<USceneComponent>(TEXT("SceneComponent"));
		MeshComp = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("MeshComp"));
		MeshComp->SetupAttachment(RootComponent, FAttachmentTransformRules::KeepRelativeTransform);

1. Compile your code.

2. In the editor, navigate to your C++ Classes folder, right-click your RotatingActor and from the C++ class actions dropdown menu, select Create Blueprint class based on RotatingActor named BP_RotatingActor.

   

3. In the class defaults for your BP_RotatingActor Blueprint, navigate to the Components tab, select the MeshComp Static Mesh Component, then navigate to the Details panel and from the Static Mesh category, select the arrow next to the Static Mesh variable. Lastly, from the dropdown menu, select the Shape_Cube static mesh.

   

4. Compile and save your Blueprint.

5. From the Content Browser, drag an instance of your Bp_RotatingActor into the Level.

   

Modifying the Third Person Character Class

In this section, you will modify the BPCommunicationCharacter class to cast to the Rotating Actor class and set the bCanRotate variable to True when your player is nearby.

1. Open your BPCommunicationCharacter.h and implement the following.

   C++

   protected:
                virtual void NotifyActorBeginOverlap(AActor* OtherActor);
                virtual void NotifyActorEndOverlap(AActor* OtherActor);
                class USphereComponent* SphereComp;

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2. In your BPCommunicationCharacter.cpp include the following class libraries

   C++

   #include "RotatingActor.h"
            #include "Components/SphereComponent.h"

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3. From the constructor ABPCommunicaionCharacter::BPCommunicationCharacter declare the following code.

   C++

   SphereComp = CreateDefaultSubobject<USphereComponent>(TEXT("SphereComp"));
            SphereComp->AttachToComponent(GetMesh(), FAttachmentTransformRules::KeepRelativeTransform);
            SphereComp->SetSphereRadius(200);

   Copy full snippet(3 lines long)

4. Next, implement the ABPCommunicationCharacter::NotifyActorBeginOverlap, and ABPCommunicationCharacter::NotifyActorEndOverlap.

   C++

   void ABPCommunicationCharacter::NotifyActorBeginOverlap(AActor* OtherActor)
            {
                if (ARotatingActor* RotatingActorCheck =Cast<ARotatingActor>(OtherActor))
                {
                    ActorCheck->SetbCanRotate(true);
                }
            }
   		
            void ABPCommunicationCharacter::NotifyActorEndOverlap(AActor* OtherActor)
            {
   
   Expand code Copy full snippet(15 lines long)

5. Compile your code.

Finished Code

BpCommunicationCharacter.h

// Copyright Epic Games, Inc. All Rights Reserved.
	#pragma once
	#include "CoreMinimal.h"
	#include "GameFramework/Character.h"
	#include "BPCommunicationCharacter.generated.h"

	UCLASS(config=Game)
	class ABPCommunicationCharacter : public ACharacter
	{
		GENERATED_BODY()

BpCommunication.cpp

// Copyright Epic Games, Inc. All Rights Reserved.
	#include "BPCommunicationCharacter.h"
	#include "HeadMountedDisplayFunctionLibrary.h"
	#include "Camera/CameraComponent.h"
	#include "Components/CapsuleComponent.h"
	#include "Components/InputComponent.h"
	#include "GameFramework/CharacterMovementComponent.h"
	#include "GameFramework/Controller.h"
	#include "GameFramework/SpringArmComponent.h"
	#include "CeilingLight.h"

1. Press Play and approach the BP_RotateActor Actor to see it rotate only when the player is nearby.

   

Next Steps

Now that you know how to use Blueprint casting, take a look at the other communication types referenced in the documentation page.