Unreal Engine 4.18中UShapeComponent类提示‘标识符未定义’的解决咨询

你遇到的标识符未定义错误，核心原因是UShapeComponent、UBoxComponent这类碰撞组件的头文件没有被手动包含，且项目可能没链接对应的Collision模块。而USceneComponent、UStaticMeshComponent能正常使用，是因为它们的头文件被GameFramework/Actor.h间接引入了，且所属的Engine模块是项目默认链接的。

1. 添加对应的组件头文件 #

在你的MyActor.h文件开头，添加需要的组件头文件。比如你用到了UShapeComponent，就加上：

#include "Components/ShapeComponent.h"

如果后续要用到UBoxComponent或USphereComponent，对应添加：

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

修改后的完整头文件如下：

#pragma once
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "Components/ShapeComponent.h" // 新增这行
#include "MyActor.generated.h"

UCLASS()
class UNREALTUROIAL_API AMyActor : public AActor
{
    GENERATED_BODY()
    
public: 
    // Sets default values for this actor's properties
    AMyActor();

protected:
    // Called when the game starts or when spawned
    virtual void BeginPlay() override;

public: 
    // Called every frame
    virtual void Tick(float DeltaTime) override;

    UPROPERTY(EditAnywhere)
    UStaticMeshComponent* PickUpMesh;

    UPROPERTY(EditAnywhere)
    UShapeComponent* PickUpBox;

    UPROPERTY(EditAnywhere)
    USceneComponent* PickUpRoot;
};

2. 检查项目Build.cs文件，确保链接Collision模块 #

找到你的项目目录下的Source/UNREALTUROIAL/UNREALTUROIAL.Build.cs文件，打开后在PublicDependencyModuleNames里添加"Collision"模块，确保代码类似：

using UnrealBuildTool;

public class UNREALTUROIAL : ModuleRules
{
    public UNREALTUROIAL(ReadOnlyTargetRules Target) : base(Target)
    {
        PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
    
        PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "Collision" });

        PrivateDependencyModuleNames.AddRange(new string[] {  });

        // Uncomment if you are using Slate UI
        // PrivateDependencyModuleNames.AddRange(new string[] { "Slate", "SlateCore" });
        
        // Uncomment if you are using online features
        // PrivateDependencyModuleNames.Add("OnlineSubsystem");

        // To include OnlineSubsystemSteam, add it to the plugins section in your uproject file with Enabled=true
    }
}

3. 重新生成项目文件并编译 #

做完上面两步后，右键你的.uproject文件，选择Generate Visual Studio project files，然后重新打开VS2017编译项目，错误应该就消失了。

Unreal采用模块化设计，每个组件类都属于特定模块：

• USceneComponent、UStaticMeshComponent属于Engine模块，项目默认会链接这个模块，且Actor.h间接包含了它们的头文件
• UShapeComponent、UBoxComponent、USphereComponent属于Collision模块，需要手动在Build.cs里添加依赖，并且包含对应的头文件才能使用

内容的提问来源于stack exchange，提问作者Imran Sikder