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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Blueprint/DontUseGenericSpawnObject/DontUseGenericSpawnObject.md

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+# DontUseGenericSpawnObject
+
+- **功能描述：** 阻止使用蓝图中的Generic Create Object节点来生成本类的对象。
+- **使用位置：** UCLASS
+- **引擎模块：** Blueprint
+- **元数据类型：** bool
+- **限制类型：** 既非Actor又非ActorComponent的BluprintType类时
+- **常用程度：** ★★
+
+用于阻止该类被通用的ConstructObject蓝图节点所构造出来。在源码里典型里使用例子是UDragDropOperation和UUserWidget，前者由UK2Node_CreateDragDropOperation这个专门的节点建出来（内部调用UWidgetBlueprintLibrary::CreateDragDropOperation），后者由CreateWidget创建。因此这种的典型用法是你自己再创建一个New的函数来自己创建该Object。
+
+## 测试代码：
+
+```cpp
+UCLASS(Blueprintable,meta=(DontUseGenericSpawnObject="true"))
+class INSIDER_API UMyClass_CustomSpawnObject :public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite,EditAnywhere)
+	float MyFloat;
+
+	UFUNCTION(BlueprintCallable)
+	static UMyClass_CustomSpawnObject* CreateMyClassObjectByMyOwnSpawn(float value)
+	{
+		UMyClass_CustomSpawnObject* obj= NewObject<UMyClass_CustomSpawnObject>();
+		obj->MyFloat=value;
+		return obj;
+	}
+};
+```
+
+## 测试效果：
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+会提前验证是否包含DontUseGenericSpawnObject元数据，因为是采用GetBoolMetaData，因此必须写上=”true”
+
+```cpp
+struct FK2Node_GenericCreateObject_Utils
+{
+	static bool CanSpawnObjectOfClass(TSubclassOf<UObject> ObjectClass, bool bAllowAbstract)
+	{
+		// Initially include types that meet the basic requirements.
+		// Note: CLASS_Deprecated is an inherited class flag, so any subclass of an explicitly-deprecated class also cannot be spawned.
+		bool bCanSpawnObject = (nullptr != *ObjectClass)
+			&& (bAllowAbstract || !ObjectClass->HasAnyClassFlags(CLASS_Abstract))
+			&& !ObjectClass->HasAnyClassFlags(CLASS_Deprecated | CLASS_NewerVersionExists);
+
+		// UObject is a special case where if we are allowing abstract we are going to allow it through even though it doesn't have BlueprintType on it
+		if (bCanSpawnObject && (!bAllowAbstract || (*ObjectClass != UObject::StaticClass())))
+		{
+			static const FName BlueprintTypeName(TEXT("BlueprintType"));
+			static const FName NotBlueprintTypeName(TEXT("NotBlueprintType"));
+			static const FName DontUseGenericSpawnObjectName(TEXT("DontUseGenericSpawnObject"));
+
+			auto IsClassAllowedLambda = [](const UClass* InClass)
+			{
+				return InClass != AActor::StaticClass()
+					&& InClass != UActorComponent::StaticClass();
+			};
+
+			// Exclude all types in the initial set by default.
+			bCanSpawnObject = false;
+			const UClass* CurrentClass = ObjectClass;
+
+			// Climb up the class hierarchy and look for "BlueprintType." If "NotBlueprintType" is seen first, or if the class is not allowed, then stop searching.
+			while (!bCanSpawnObject && CurrentClass != nullptr && !CurrentClass->GetBoolMetaData(NotBlueprintTypeName) && IsClassAllowedLambda(CurrentClass))
+			{
+				// Include any type that either includes or inherits 'BlueprintType'
+				bCanSpawnObject = CurrentClass->GetBoolMetaData(BlueprintTypeName);
+
+				// Stop searching if we encounter 'BlueprintType' with 'DontUseGenericSpawnObject'
+				if (bCanSpawnObject && CurrentClass->GetBoolMetaData(DontUseGenericSpawnObjectName))
+				{
+					bCanSpawnObject = false;
+					break;
+				}
+
+				CurrentClass = CurrentClass->GetSuperClass();
+			}
+
+			// If we validated the given class, continue walking up the hierarchy to make sure we exclude it if it's an Actor or ActorComponent derivative.
+			while (bCanSpawnObject && CurrentClass != nullptr)
+			{
+				bCanSpawnObject &= IsClassAllowedLambda(CurrentClass);
+
+				CurrentClass = CurrentClass->GetSuperClass();
+			}
+		}
+
+		return bCanSpawnObject;
+	}
+};
+```