BlueprintInternalUseOnly

功能描述： 不可定义新BP变量，但可作为别的类的成员变量暴露和变量传递
元数据类型： bool
引擎模块： Blueprint
作用机制： 在Meta中加入BlueprintInternalUseOnly, BlueprintType
常用程度： ★★

指明这个STRUCT会是个BlueprintType，但在蓝图编辑器中又不能声明新变量，但是可以作为别的类的成员变量暴露到蓝图中。

和不写BlueprintType的差别是什么？

不写BlueprintType则完全不能作为别的类的成员变量。BlueprintInternalUseOnly抑制了定义新变量的能力，但是可以作为变量传递。比如在C++中定义变量，然后在蓝图中传递。

如FTableRowBase本身并不能定义新变量，但是其子类（要加上BlueprintType）是可以定义新变量的，正常被使用。

示例代码：

//(BlueprintInternalUseOnly = true, BlueprintType = true, ModuleRelativePath = Struct/MyStruct_BlueprintInternalUseOnly.h)
USTRUCT(BlueprintInternalUseOnly)
struct INSIDER_API FMyStruct_BlueprintInternalUseOnly
{
	GENERATED_BODY()

	UPROPERTY(BlueprintReadWrite,EditAnywhere)
	float Score=0.f;
};

USTRUCT()
struct INSIDER_API FMyStruct_NoBlueprintInternalUseOnly
{
	GENERATED_BODY()

	UPROPERTY(EditAnywhere)
	float Score=0.f;
};

UCLASS(Blueprintable,BlueprintType)
class INSIDER_API UMyClass_BlueprintInternalUseOnlyTest :public UObject
{
	GENERATED_BODY()
public:
	UPROPERTY(BlueprintReadWrite,EditAnywhere)
	FMyStruct_BlueprintInternalUseOnly MyInternalStruct;

	/*UPROPERTY(BlueprintReadWrite,EditAnywhere)	//no supported by BP
	FMyStruct_NoBlueprintInternalUseOnly MyStruct;*/
};

示例效果：

NewVar是UMyClass_BlueprintInternalUseOnlyTest 类型的，依然可以访问内部的MyInternalStruct变量。

源码里可以找到：

USTRUCT(BlueprintInternalUseOnly)
struct FLatentActionInfo
{}

USTRUCT(BlueprintInternalUseOnly)
struct FTableRowBase
{}

原理：

bool UEdGraphSchema_K2::IsAllowableBlueprintVariableType(const UScriptStruct* InStruct, const bool bForInternalUse)
{
	if (const UUserDefinedStruct* UDStruct = Cast<const UUserDefinedStruct>(InStruct))
	{
		if (EUserDefinedStructureStatus::UDSS_UpToDate != UDStruct->Status.GetValue())
		{
			return false;
		}

		// User-defined structs are always allowed as BP variable types.
		return true;
	}

	// struct needs to be marked as BP type
	if (InStruct && InStruct->GetBoolMetaDataHierarchical(FBlueprintMetadata::MD_AllowableBlueprintVariableType))
	{
		// for internal use, all BP types are allowed
		if (bForInternalUse)
		{
			return true;
		}

		// for user-facing use case, only allow structs that don't have the internal-use-only tag
		// struct itself should not be tagged
		if (!InStruct->GetBoolMetaData(FBlueprintMetadata::MD_BlueprintInternalUseOnly))
		{
			// struct's base structs should not be tagged
			if (!InStruct->GetBoolMetaDataHierarchical(FBlueprintMetadata::MD_BlueprintInternalUseOnlyHierarchical))
			{
				return true;
			}
		}
	}

	return false;
}

//Node->IsIntermediateNode()如果为true，则是作为中间节点使用，true会导致bForInternalUse为true
if (!UK2Node_MakeStruct::CanBeMade(Node->StructType, Node->IsIntermediateNode()))

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BlueprintInternalUseOnly

示例代码：

示例效果：

原理：

3.3 KiB

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