c++ - 虚幻 : "Unknown type name UTextRenderComponent" compile error while following tutorial

Question

我正在关注 this tutorial我从字面上复制并粘贴了 Countdown.h 和 Countdown.cpp 的内容。

Visual Studio Code(我在 mac 上)给出了以下提示

#include errors detected. Please update your includePath. IntelliSense features for this translation unit (/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h) will be provided by the Tag Parser.
cannot open source file "new" (dependency of "GameFramework/Actor.h")

在这条线上

#include "GameFramework/Actor.h"

而我从UE得到的编译错误如下

Running Mono...

Setting up Mono
~/Documents/UE_4.18/Engine ~/Documents/UE_4.18/Engine/Binaries/Mac
Compiling game modules for hot reload
Parsing headers for HowTo_VTEEditor
  Running UnrealHeaderTool "/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/HowTo_VTE.uproject" "/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/HowTo_VTEEditor/Development/HowTo_VTEEditor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -installed
Reflection code generated for HowTo_VTEEditor in 10,277899 seconds
Performing 3 actions (5 in parallel)
[2/3] Compile Countdown.cpp
[1/3] Compile Countdown.gen.cpp
In file included from /Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.gen.cpp:8:
../../../Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h:29:5: error: unknown type name 'UTextRenderComponent'
    UTextRenderComponent* CountdownText;
    ^
../../../Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h:12:5: error: cannot initialize return object of type 'UObject *' with an rvalue of type 'ACountdown *'
    GENERATED_BODY()
    ^~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:585:29: note: expanded from macro 'GENERATED_BODY'
#define GENERATED_BODY(...) BODY_MACRO_COMBINE(CURRENT_FILE_ID,_,__LINE__,_GENERATED_BODY);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:580:37: note: expanded from macro 'BODY_MACRO_COMBINE'
#define BODY_MACRO_COMBINE(A,B,C,D) BODY_MACRO_COMBINE_INNER(A,B,C,D)
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:579:43: note: expanded from macro 'BODY_MACRO_COMBINE_INNER'
#define BODY_MACRO_COMBINE_INNER(A,B,C,D) A##B##C##D
                                          ^~~~~~~~~~
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../../../Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.generated.h:81:2: note: expanded from macro 'HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_GENERATED_BODY'
        HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_ENHANCED_CONSTRUCTORS \
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.generated.h:57:54: note: expanded from macro 'HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_ENHANCED_CONSTRUCTORS'
        DECLARE_VTABLE_PTR_HELPER_CTOR(NO_API, ACountdown); \
                                                            ^
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:1387:11: note: expanded from macro '\
DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER'
                        return new (EC_InternalUseOnlyConstructor, (UObject*)GetTransientPackage(), NAME_None, RF_NeedLoad | RF_ClassDefaultObject | RF_TagGarbageTemp) TClass(Helper); \
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:1:
../../../Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h:29:5: error: unknown type name 'UTextRenderComponent'
    UTextRenderComponent* CountdownText;
    ^
../../../Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h:12:5: error: cannot initialize return object of type 'UObject *' with an rvalue of type 'ACountdown *'
    GENERATED_BODY()
    ^~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:585:29: note: expanded from macro 'GENERATED_BODY'
#define GENERATED_BODY(...) BODY_MACRO_COMBINE(CURRENT_FILE_ID,_,__LINE__,_GENERATED_BODY);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:580:37: note: expanded from macro 'BODY_MACRO_COMBINE'
#define BODY_MACRO_COMBINE(A,B,C,D) BODY_MACRO_COMBINE_INNER(A,B,C,D)
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:579:43: note: expanded from macro 'BODY_MACRO_COMBINE_INNER'
#define BODY_MACRO_COMBINE_INNER(A,B,C,D) A##B##C##D
                                          ^~~~~~~~~~
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../../../Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.generated.h:81:2: note: expanded from macro 'HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_GENERATED_BODY'
        HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_ENHANCED_CONSTRUCTORS \
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.generated.h:57:54: note: expanded from macro 'HowTo_VTE_Source_HowTo_VTE_Countdown_h_12_ENHANCED_CONSTRUCTORS'
        DECLARE_VTABLE_PTR_HELPER_CTOR(NO_API, ACountdown); \
                                                            ^
Runtime/CoreUObject/Public/UObject/ObjectMacros.h:1387:11: note: expanded from macro '\
DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER'
                        return new (EC_InternalUseOnlyConstructor, (UObject*)GetTransientPackage(), NAME_None, RF_NeedLoad | RF_ClassDefaultObject | RF_TagGarbageTemp) TClass(Helper); \
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:11:44: error: use of undeclared identifier 'UTextRenderComponent'
    CountdownText = CreateDefaultSubobject<UTextRenderComponent>(TEXT("CountdownNumber"));
                                           ^
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:12:43: error: use of undeclared identifier 'EHTA_Center'; did you mean 'kTXNCenter'?
    CountdownText->SetHorizontalAlignment(EHTA_Center);
                                          ^~~~~~~~~~~
                                          kTXNCenter
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Carbon.framework/Frameworks/HIToolbox.framework/Headers/MacTextEditor.h:793:3: note: 'kTXNCenter' declared here
  kTXNCenter                    = 4,
  ^
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:22:12: error: cannot initialize object parameter of type 'AActor' with an expression of type 'ACountdown'
    Super::BeginPlay();
           ^~~~~~~~~
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:25:5: error: cannot initialize object parameter of type 'const AActor' with an expression of type 'ACountdown'
    GetWorldTimerManager().SetTimer(CountdownTimerHandle, this, &ACountdown::AdvanceTimer, 1.0f, true);
    ^~~~~~~~~~~~~~~~~~~~
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:31:12: error: no matching member function for call to 'Tick'
    Super::Tick( DeltaTime );
    ~~~~~~~^~~~
Runtime/Engine/Classes/GameFramework/Actor.h:2077:15: note: candidate function not viable: no known conversion from 'ACountdown' to 'AActor' for object argument
        virtual void Tick( float DeltaSeconds );
                     ^
Runtime/Engine/Classes/GameFramework/Actor.h:2432:15: note: candidate function not viable: requires 2 arguments, but 1 was provided
        virtual void Tick( float DeltaTime, enum ELevelTick TickType ) final
                     ^
/Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.cpp:47:9: error: cannot initialize object parameter of type 'const AActor' with an expression of type 'ACountdown'
        GetWorldTimerManager().ClearTimer(CountdownTimerHandle);
        ^~~~~~~~~~~~~~~~~~~~
2 errors generated.
8 errors generated.
ERROR: UBT ERROR: Failed to produce item: /Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Binaries/Mac/UE4Editor-HowTo_VTE-6063.dylib
Total build time: 28,61 seconds (Local executor: 0,00 seconds)

好像这两个错误是相关的，但我不明白可能出了什么问题。我注意到虽然我的项目位于 /Documents/Unreal Projects/HowTo_VTE/Source/HowToVTE/Countdown.cpp虚幻的东西在 Documents/UE_4.18/Engine/...这可能是找不到包含的罪魁祸首吗？

编辑:我尝试使用 Actor.h 的绝对路径包含，但我得到了相同的编译错误

Answer 1

以下是了解此错误告诉您的内容的方法:

[1/3] Compile Countdown.gen.cpp
In file included from /Users/massimobortolamei/Documents/Unreal Projects/HowTo_VTE/Intermediate/Build/Mac/UE4Editor/Inc/HowTo_VTE/Countdown.gen.cpp:8:
../../../Unreal Projects/HowTo_VTE/Source/HowTo_VTE/Countdown.h:29:5: error: unknown type name 'UTextRenderComponent'
    UTextRenderComponent* CountdownText;
    ^

您的编译器告诉您它不知道 UTextRenderComponent 是什么，因为尚未包含定义它的文件。这就是添加 include (#include "Runtime/Engine/Classes/Components/TextRenderComponent.h") 的原因。但是，在现有 header 中包含其他 header 通常不是一个好主意，因为这会增加大型项目的编译时间(Here's 对为什么会这样的解释。)

更好的做法是在 header 中前向声明 UTextRenderComponent，然后在 .cpp 文件中包含 TextRenderComponent header 。 (Some info 关于前向声明)Unreal 的构建工具提供了一种使用 class 关键字执行此操作的便捷方法。

像这样声明你的成员变量:

class UTextRenderComponent* CountdownText;

然后在您的 .cpp 文件中包含所需的 header 。您在此实例中所做的是告诉您的编译器 UTextRenderComponent 是一个类，并且您 promise 稍后提供定义。您的编译器在解析 Countdown.h 时不需要知道该定义是什么，因为您只是包含一个指向该类的指针，所以它不需要知道它的大小或任何其他有关它的信息 - 只是它是一个在别处定义的类。

所以是的，您在上面找到的解决方案可以工作，但不如在您的 header 中转发声明您的类然后在您的实现中包含其他 header 那么理想。