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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/UCLASS/Scene/NotPlaceable/NotPlaceable.md

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+# NotPlaceable
+
+- **功能描述：** 标明该Actor不可被放置在关卡里
+- **引擎模块：** Behavior
+- **元数据类型：** bool
+- **作用机制：** 在ClassFlags中添加[CLASS_NotPlaceable](../../../../Flags/EClassFlags/CLASS_NotPlaceable.md)
+- **关联项：** Placeable (Placeable.md)
+- **常用程度：★★★**
+
+标明该Actor不可被放置在关卡里，没法拖放到场景里。使继承自基类的Placeable说明符无效。会在ClassFlagss里标记上CLASS_NotPlaceable，这个标记是可以继承的，意味着其所有的子类默认都不可放置。例如AWorldSettings其实就是一个notplaceable的Actor。
+
+但是注意该类依然可以通过SpawnActor动态生成到关卡中。
+
+NotPlaceable的类是不出现在PlaceMode的类选择里去的。
+
+## 示例代码：
+
+```cpp
+UCLASS(Blueprintable,BlueprintType, NotPlaceable)
+class INSIDER_API AMyActor_NotPlaceable :public AActor
+{
+	GENERATED_BODY()
+};
+```
+
+## 示例效果：
+
+拖动到场景里会发现不能创建Actor。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+如果直接是C++类AMyActor_NotPlaceable ，是可以直接从ContentBrowser拖到场景里去的。看源码可知，只有BP继承下来的子类才有受到这个限制。
+
+```cpp
+TArray<AActor*> FLevelEditorViewportClient::TryPlacingActorFromObject( ULevel* InLevel, UObject* ObjToUse, bool bSelectActors, EObjectFlags ObjectFlags, UActorFactory* FactoryToUse, const FName Name, const FViewportCursorLocation* Cursor )
+{
+
+	bool bPlace = true;
+	if (ObjectClass->IsChildOf(UBlueprint::StaticClass()))
+	{
+		UBlueprint* BlueprintObj = StaticCast<UBlueprint*>(ObjToUse);
+		bPlace = BlueprintObj->GeneratedClass != NULL;
+		if(bPlace)
+		{
+			check(BlueprintObj->ParentClass == BlueprintObj->GeneratedClass->GetSuperClass());
+			if (BlueprintObj->GeneratedClass->HasAnyClassFlags(CLASS_NotPlaceable | CLASS_Abstract))
+			{
+				bPlace = false;
+			}
+		}
+	}
+
+	if (bPlace)
+	{
+		PlacedActor = FActorFactoryAssetProxy::AddActorForAsset( ObjToUse, bSelectActors, ObjectFlags, FactoryToUse, Name );
+		if ( PlacedActor != NULL )
+		{
+			PlacedActors.Add(PlacedActor);
+			PlacedActor->PostEditMove(true);
+		}
+	}
+}
+```