虚幻：遵循教程时，“未知类型名称UTextRenderComponent”编译错误

Question

I'm following this tutorial and I literally copied and pasted the content of Countdown.h and Countdown.cpp.

Visual Studio Code (I'm on mac) gives the following hint

#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")

at this line

#include "GameFramework/Actor.h"

while the compilation error I get from UE is the following

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)

It's as if the two errors are related, but I don't get what could be wrong. I noticed that while my project is situated in /Documents/Unreal Projects/HowTo_VTE/Source/HowToVTE/Countdown.cpp the Unreal stuff is in Documents/UE_4.18/Engine/... could this be the culprit for which the include is not found?

edit: i tried the include with the absolute path to Actor.h but i get the same compile error

Answer 1

I posted this same question on the Answerhub of Unreal, and a kind user was able to provide a solution.

You can see it here

For short: add #include "Runtime/Engine/Classes/Components/TextRenderComponent.h" to the includes in Countdown.h (Leaving the autogenerated include as last, of course)

Answer 2

Here's how to understand what this error was telling you:

[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;
    ^

Your compiler is telling you that it doesn't know what a UTextRenderComponent is because the file that defines it hasn't yet been included. This is why adding the include ( #include "Runtime/Engine/Classes/Components/TextRenderComponent.h" ) worked. It's not, however, generally a good idea to include other headers in your existing headers, as this will bloat your compile times on large projects ( Here's a decent explanation of why this is.)

A better practice is to forward-declare the UTextRenderComponent in your header, and then include the TextRenderComponent header in your .cpp file. ( Some info about forward declarations) Unreal's build tool provides a convenient way to do this using the class keyword.

Declare your member variable like this:

class UTextRenderComponent* CountdownText;

And then include the required header in your .cpp file. What you're doing in this instance is telling your compiler that UTextRenderComponent is a class, and you're promising to supply the definition later on. Your compiler doesn't need to know what that definition is while it's parsing Countdown.h because you're just including a pointer to the class, so it doesn't need to know its size or anything else about it - just that it's a class defined somewhere else.

So yes, the solution you found above will work but is less ideal than forward-declaring your class in your header and then including other headers in your implementation.