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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/USTRUCT/Blueprint/BlueprintInternalUseOnly/BlueprintInternalUseOnly.md

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+# 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](../../../../Meta/Blueprint/BlueprintInternalUseOnly.md), [BlueprintType](../../../../Meta/Blueprint/BlueprintType.md)
+- **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：
+
+```cpp
+//(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。
+
+![Untitled](Untitled.png)
+
+源码里可以找到：
+
+```cpp
+USTRUCT(BlueprintInternalUseOnly)
+struct FLatentActionInfo
+{}
+
+USTRUCT(BlueprintInternalUseOnly)
+struct FTableRowBase
+{}
+```
+
+## 原理：
+
+```cpp
+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()))
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/USTRUCT/Blueprint/BlueprintInternalUseOnlyHierarchical.md

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+# BlueprintInternalUseOnlyHierarchical
+
+- **功能描述：**  在BlueprintInternalUseOnly的基础上，增加了子类也不能定义新BP变量的限制。
+- **元数据类型：** bool
+- **引擎模块：** Blueprint
+- **作用机制：** 在Meta中加入[BlueprintInternalUseOnlyHierarchical](../../../Meta/Blueprint/BlueprintInternalUseOnlyHierarchical.md)
+- **常用程度：★**
+
+在BlueprintInternalUseOnly的基础上，增加了子类也不能定义新BP变量的限制。
+
+目前只找到一个用处，但是也依然没有子类。如果我们在C++中定义新的子类，则所有的子类都不能定义变量。注意和FTableRowBase的区别是，FTableRowBase的子类依然可以定义新变量，因为FTableRowBase的BlueprintInternalUseOnly标记只作用于自己。
+
+## 示例代码：
+
+```cpp
+USTRUCT(BlueprintInternalUseOnlyHierarchical)
+struct GAMEPLAYABILITIESEDITOR_API FGameplayAbilityAuditRow : public FTableRowBase
+{}
+
+USTRUCT(BlueprintInternalUseOnly)
+struct FTableRowBase
+{}
+```
+
+## 原理：
+
+只在这个地方用到，GetBoolMetaDataHierarchical会检查结构的所有父类测试是否含有某个标记。所以只要有一个父类有一个这个标记，就不能定义新变量。
+
+```cpp
+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;
+}
+
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/USTRUCT/Blueprint/BlueprintType/BlueprintType.md

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+# BlueprintType
+
+- **功能描述：**  允许这个结构在蓝图中声明变量
+- **元数据类型：** bool
+- **引擎模块：** Blueprint
+- **作用机制：** 在Meta中加入[BlueprintType](../../../../Meta/Blueprint/BlueprintType.md)
+- **常用程度：★★★★★**
+
+和UCLASS里的一样，可以允许这个结构在蓝图中声明变量
+
+## 示例代码：
+
+```cpp
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStruct_BlueprintType
+{
+	GENERATED_BODY()
+
+	UPROPERTY(BlueprintReadWrite,EditAnywhere)
+	float Score;
+};
+
+USTRUCT()
+struct INSIDER_API FMyStruct_NoBlueprintType
+{
+	GENERATED_BODY()
+
+	UPROPERTY(EditAnywhere)
+	float Score;
+};
+```
+
+## 测试蓝图：
+
+![Untitled](Untitled.png)