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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/UCLASS/Blueprint/Blueprintable/Blueprintable.md

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+# Blueprintable
+
+- **功能描述：** 可以在蓝图里被继承，隐含的作用也可当变量类型
+- **引擎模块：** Blueprint
+- **元数据类型：** bool
+- **作用机制：** 在Meta添加[IsBlueprintBase](../../../../Meta/Blueprint/IsBlueprintBase.md)和[BlueprintType](../../../../Meta/Blueprint/BlueprintType.md)
+- **关联项：** [NotBlueprintable](../NotBlueprintable.md)
+- **常用程度：** ★★★★★
+
+可以在蓝图里被继承，隐含的作用也可当变量类型。
+
+当设置Blueprintable标记的时候，会隐含的设置上BlueprintType = true的metadata。去除的时候，也会相应的去除掉BlueprintType = true。
+
+## 示例代码：
+
+```cpp
+/*
+(BlueprintType = true, IncludePath = Class/MyClass_Blueprintable.h, IsBlueprintBase = true, ModuleRelativePath = Class/MyClass_Blueprintable.h)
+*/
+UCLASS(Blueprintable)
+class INSIDER_API UMyClass_Blueprintable :public UObject
+{
+	GENERATED_BODY()
+};
+
+/*
+(IncludePath = Class/MyClass_Blueprintable.h, IsBlueprintBase = false, ModuleRelativePath = Class/MyClass_Blueprintable.h)
+*/
+UCLASS(NotBlueprintable)
+class INSIDER_API UMyClass_NotBlueprintable :public UObject
+{
+	GENERATED_BODY()
+};
+
+/*
+(BlueprintType = true, IncludePath = Class/MyClass_Blueprintable.h, IsBlueprintBase = true, ModuleRelativePath = Class/MyClass_Blueprintable.h)
+*/
+UCLASS(Blueprintable)
+class INSIDER_API UMyClass_NotBlueprintable_To_Blueprintable :public UMyClass_NotBlueprintable
+{
+	GENERATED_BODY()
+};
+
+/*
+(IncludePath = Class/MyClass_Blueprintable.h, IsBlueprintBase = false, ModuleRelativePath = Class/MyClass_Blueprintable.h)
+*/
+UCLASS(NotBlueprintable)
+class INSIDER_API UMyClass_Blueprintable_To_NotBlueprintable :public UMyClass_Blueprintable
+{
+	GENERATED_BODY()
+};
+```
+
+## 示例效果：
+
+只有带有Blueprintable才可以被选做基类。
+
+![Untitled](Untitled.png)
+
+不过是否能够当做变量的规则，还是会依赖父类的Blueprint标记。因此以下这3个都是可以当做变量的。
+
+其中UMyClass_Blueprintable_To_NotBlueprintable可以当做变量是因为父类UMyClass_Blueprintable可以当做变量，因此就继承了下来。
+
+![Untitled](Untitled%201.png)
+
+## 原理：
+
+可见MD_IsBlueprintBase的判断用来决定是否能创建子类
+
+```cpp
+bool FKismetEditorUtilities::CanCreateBlueprintOfClass(const UClass* Class)
+{
+	bool bCanCreateBlueprint = false;
+	
+	if (Class)
+	{
+		bool bAllowDerivedBlueprints = false;
+		GConfig->GetBool(TEXT("Kismet"), TEXT("AllowDerivedBlueprints"), /*out*/ bAllowDerivedBlueprints, GEngineIni);
+
+		bCanCreateBlueprint = !Class->HasAnyClassFlags(CLASS_Deprecated)
+			&& !Class->HasAnyClassFlags(CLASS_NewerVersionExists)
+			&& (!Class->ClassGeneratedBy || (bAllowDerivedBlueprints && !IsClassABlueprintSkeleton(Class)));
+
+		const bool bIsBPGC = (Cast<UBlueprintGeneratedClass>(Class) != nullptr);
+
+		const bool bIsValidClass = Class->GetBoolMetaDataHierarchical(FBlueprintMetadata::MD_IsBlueprintBase)
+			|| (Class == UObject::StaticClass())
+			|| (Class == USceneComponent::StaticClass() || Class == UActorComponent::StaticClass())
+			|| bIsBPGC;  // BPs are always considered inheritable
+			
+		bCanCreateBlueprint &= bIsValidClass;
+	}
+	
+	return bCanCreateBlueprint;
+}
+```