113 lines
3.3 KiB
Markdown
113 lines
3.3 KiB
Markdown
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# BlueprintInternalUseOnly
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- **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
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- **元数据类型：** bool
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- **引擎模块：** Blueprint
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- **作用机制：** 在Meta中加入[BlueprintInternalUseOnly](../../../../Meta/Blueprint/BlueprintInternalUseOnly.md), [BlueprintType](../../../../Meta/Blueprint/BlueprintType.md)
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- **常用程度：** ★★
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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。
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和不写BlueprintType的差别是什么？
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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。
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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。
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## 示例代码：
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```cpp
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//(BlueprintInternalUseOnly = true, BlueprintType = true, ModuleRelativePath = Struct/MyStruct_BlueprintInternalUseOnly.h)
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USTRUCT(BlueprintInternalUseOnly)
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struct INSIDER_API FMyStruct_BlueprintInternalUseOnly
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{
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GENERATED_BODY()
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UPROPERTY(BlueprintReadWrite,EditAnywhere)
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float Score=0.f;
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};
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USTRUCT()
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struct INSIDER_API FMyStruct_NoBlueprintInternalUseOnly
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{
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GENERATED_BODY()
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UPROPERTY(EditAnywhere)
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float Score=0.f;
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};
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UCLASS(Blueprintable,BlueprintType)
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class INSIDER_API UMyClass_BlueprintInternalUseOnlyTest :public UObject
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{
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GENERATED_BODY()
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public:
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UPROPERTY(BlueprintReadWrite,EditAnywhere)
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FMyStruct_BlueprintInternalUseOnly MyInternalStruct;
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/*UPROPERTY(BlueprintReadWrite,EditAnywhere) //no supported by BP
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FMyStruct_NoBlueprintInternalUseOnly MyStruct;*/
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};
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```
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## 示例效果：
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NewVar是UMyClass_BlueprintInternalUseOnlyTest 类型的，依然可以访问内部的MyInternalStruct变量。
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源码里可以找到：
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```cpp
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USTRUCT(BlueprintInternalUseOnly)
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struct FLatentActionInfo
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{}
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USTRUCT(BlueprintInternalUseOnly)
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struct FTableRowBase
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{}
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```
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## 原理：
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```cpp
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bool UEdGraphSchema_K2::IsAllowableBlueprintVariableType(const UScriptStruct* InStruct, const bool bForInternalUse)
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{
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if (const UUserDefinedStruct* UDStruct = Cast<const UUserDefinedStruct>(InStruct))
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{
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if (EUserDefinedStructureStatus::UDSS_UpToDate != UDStruct->Status.GetValue())
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{
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return false;
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}
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// User-defined structs are always allowed as BP variable types.
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return true;
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}
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// struct needs to be marked as BP type
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if (InStruct && InStruct->GetBoolMetaDataHierarchical(FBlueprintMetadata::MD_AllowableBlueprintVariableType))
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{
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// for internal use, all BP types are allowed
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if (bForInternalUse)
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{
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return true;
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}
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// for user-facing use case, only allow structs that don't have the internal-use-only tag
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// struct itself should not be tagged
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if (!InStruct->GetBoolMetaData(FBlueprintMetadata::MD_BlueprintInternalUseOnly))
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{
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// struct's base structs should not be tagged
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if (!InStruct->GetBoolMetaDataHierarchical(FBlueprintMetadata::MD_BlueprintInternalUseOnlyHierarchical))
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{
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return true;
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}
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}
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}
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return false;
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}
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//Node->IsIntermediateNode()如果为true，则是作为中间节点使用，true会导致bForInternalUse为true
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if (!UK2Node_MakeStruct::CanBeMade(Node->StructType, Node->IsIntermediateNode()))
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```
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