Note: This page is still a work in progress. There are a lot of meta specifiers still to document!
Unreal's Class Specifiers and Class Metadata Specifiers pages list all of the core specifiers and many of the metadata specifiers, but it is not an exhaustive list.
This page attempts to be an exhaustive list of all the UCLASS specifiers,
giving explanations, sample code, screenshots and related links for each.
If you know of any not listed here, or see any mistakes, feel free to contact me.
Special thanks to Erekose Craft, Ben Fox, Aquanox, ATankNoMore for finding meta properties, giving feedback and giving great examples of usage.
The YAML files used to generate this documentation are available on GitHub. Feel free to submit pull requests or submit any incorrect or missing information there.
General Points
- Tags are case insensitive, but I would recommend sticking to the case example here for readability.
- Quotation marks are optional if the values does not have spaces. e.g.
someBool=trueis treated the same assomeBool="true". Again, for readability I would recommend using quotation marks only around string-type properties.
Display
UCLASS(
AdvancedClassDisplay
)Position:
Main
Type:
flag
The AdvancedClassDisplay Specifier forces all properties of the class to show only in the advanced sections of any details panel where they appear. To override this on an individual property, use the SimpleDisplay specifier on that property.
UCLASS(
ClassGroup
="abc")Position:
Main
Type:
string
Class Group must be something already registered, you can't put arbitrary strings in here.
Seems to be only used for the Add Component button within an actor.
Indicates that Unreal Editor's Actor Browser should include this class and any subclass of this class within the specified GroupName when Group View is enabled in the Actor Browser.
UCLASS(ClassGroup="Animation")
class UMyActorComponent : public UActorComponent
{
GENERATED_BODY()
};
UCLASS(
AutoCollapseCategories
="abc")Position:
Main
Type:
string (Comma-separated list)
Incompatible with:
Opposite:
The AutoCollapseCategories Specifier negates the effects, for the listed categories, of the AutoExpandCategories Specifier on a parent class.
UCLASS(
DontAutoCollapseCategories
="abc")Negates the AutoCollapseCategories Specifier for the listed categories inherited from a parent class.
UCLASS(
AutoExpandCategories
="abc")Specifies one or more categories that should be automatically expanded in the Unreal Editor Property window for Objects of this class. To auto-expand variables declared with no category, use the name of the class which declares the variable.
UCLASS(
CollapseCategories
)Indicates that properties of this class should not be grouped in categories in Unreal Editor Property windows. This Specifier is propagated to child classes, and can be overridden by the DontCollapseCategories Specifier.
UCLASS(
DontCollapseCategories
)Negates a CollapseCatogories Specifier inherited from a base class.
UCLASS(
Hidden
)Position:
Main
Type:
flag
The UCLASS specifier now takes a Hidden flag. This maps directly to the ClassFlags Enum CLASS_Hidden flag. Adding this flag will hide the given class from any class browser in the editor.
UCLASS(
HideDropdown
)Position:
Main
Type:
flag
Prevents this class from showing up in property window combo boxes.
UCLASS(
ShowCategories
="abc")Negates a HideCategories Specifier (inherited from a base class) for the listed categories.
UCLASS(
HideCategories
="abc")Lists one or more categories that should be hidden from the user entirely. To hide properties declared with no category, use the name of the class which declares the variable. This Specifier is propagated to child classes.
UCLASS(meta=(
PrioritizeCategories
="abc"))Position:
Meta
Type:
string (comma-separated category names)
Related:
Only seems to be used in one place in the source, UCommonTextBlock. Seems to cause the specified categories to be shown first.
UCLASS(Config = CommonUI, DefaultConfig, ClassGroup = UI, meta = (Category = "Common UI", DisplayName = "Common Text", PrioritizeCategories = "Content"))
class COMMONUI_API UCommonTextBlock : public UTextBlock
UCLASS(meta=(
IgnoreCategoryKeywordsInSubclasses
))Position:
Meta
Type:
flag
Related:
A child that subclasses a class with this meta tag will ignore the following specifiers in the parent: ShowCategories, HideCategories, AutoExpandCategories, AutoCollapseCategories and PrioritizeCategories.
Only used in one place in the codebase. ComponentWrapperClass is an odd alias for it.
Used to make the first subclass of a class ignore all inherited ShowCategories and HideCategories Specifiers.
UCLASS(meta=(
ToolTip
="abc"))Position:
Meta
Type:
string
Related:
TODO Look into how this is different to ShortToolTip
Overrides the automatically generated tooltip from code comments.
UCLASS(meta=(
ShortToolTip
="abc"))Position:
Meta
Type:
string
Related:
TODO Look into how this is different to ToolTip
A short tooltip that is used in some contexts where the full tooltip might be overwhelming, such as the Parent Class Picker dialog.
UCLASS(meta=(ShortTooltip="A layout panel for automatically laying child widgets out vertically"))
class UMG_API UVerticalBox : public UPanelWidget
Blueprint
UCLASS(
Abstract
)Position:
Main
Type:
flag
The Abstract Specifier declares the class as an "abstract base class", preventing the user from adding Actors of this class to Levels. This is useful for classes which are not meaningful on their own. For example, the ATriggerBase base class is abstract, while the ATriggerBox subclass is not abstract and can be placed in a Level.
// I am abstract, you can't instantiate me!
UCLASS(Abstract)
class UAnimalBase : public UObject
{
GENERATED_BODY()
public:
UAnimalBase(const FObjectInitializer& ObjectInitializer);
};
UCLASS(
Blueprintable
)Exposes this class as an acceptable base class for creating Blueprints. The default is NotBlueprintable, unless inherited otherwise. This Specifier is inherited by subclasses.
UCLASS(
NotBlueprintable
)Specifies that this class is not an acceptable base class for creating Blueprints. This is the default and is inherited by subclasses.
UCLASS(meta=(
IsBlueprintBase
=true))Position:
Meta
Type:
bool
Related:
Is much less frequently used than Blueprintable and NotBlueprintable. I would stick to those.
States that this class is (or is not) an acceptable base class for creating Blueprints, similar to the Blueprintable or 'NotBlueprintable' Specifiers.
UCLASS(
BlueprintType
)Position:
Main
Type:
flag
Exposes this class as a type that can be used for variables in Blueprints.
UCLASS(BlueprintType)
class UExampleObject : public UObject
UCLASS(
Const
)Position:
Main
Type:
flag
Related:
Not entirely sure what difference this makes or when to use it.
All properties and functions in this class are const and are exported as const. This Specifier is inherited by subclasses.
UCLASS(meta=(
BlueprintSpawnableComponent
))Position:
Meta
Type:
flag
Adding this means that the component will appear under the "Add" dropdown for adding components to an Actor.
If present, the component Class can be spawned by a Blueprint.
UCLASS(meta=(
BlueprintThreadSafe
))Position:
Meta
Type:
flag
Only valid on Blueprint function libraries. This specifier marks the functions in this class as callable on non-game threads in animation Blueprints.
UCLASS(meta=(
ShowWorldContextPin
))Position:
Meta
Type:
flag
Indicates that Blueprint nodes placed in graphs owned by this class must show their World context pins, even if they are normally hidden, because Objects of this class cannot be used as World context.
Config
UCLASS(
Config
="abc")Position:
Main
Type:
string
Indicates that this class is allowed to store data in a configuration file (.ini). If there are any class properties declared with the config or globalconfig Specifiers, this Specifier causes those properties to be stored in the named configuration file. This Specifier is propagated to all child classes and cannot be negated, but child classes can change the config file by re-declaring the config Specifier and providing a different ConfigName. Common ConfigName values are "Engine", "Editor", "Input", and "Game".
UCLASS(
DefaultConfig
)UCLASS(
PerObjectConfig
)Configuration information for this class will be stored per Object, where each object has a section in the .ini file named after the Object in the format [ObjectName ClassName]. This Specifier is propagated to child classes.
UCLASS(
ConfigDoNotCheckDefaults
)UCLASS(
GlobalUserConfig
)UCLASS(
ProjectUserConfig
)Todo
UCLASS(
ConversionRoot
)Position:
Main
Type:
flag
Related:
Not entirely sure what this does.
Seems to co-occur with ComponentWrapperClass pretty often.
As a odd aside, it seems that IsConversionRoot=true is metadata that is assigned by the engine when it finds the ConversionRoot non-meta flag.
A root convert limits a subclass to only be able to convert to child classes of the first root class going up the hierarchy.
UCLASS(
Deprecated
)Position:
Main
Type:
flag
This class is deprecated and Objects of this class will not be saved when serializing. This Specifier is inherited by subclasses.
UCLASS(meta=(
ChildCanTick
))Used for Actor and Component classes. If the native class cannot tick, Blueprint-generated classes based this Actor or Component can have the bCanEverTick flag overridden, even if bCanBlueprintsTickByDefault is false.
UCLASS(meta=(
ChildCannotTick
))Used for Actor and Component classes. If the native class cannot tick, Blueprint-generated classes based this Actor or Component can never tick, even if bCanBlueprintsTickByDefault is true.
UCLASS(meta=(
DeprecatedNode
))Position:
Meta
Type:
flag
For behavior tree nodes, indicates that the class is deprecated and will display a warning when compiled.
UCLASS(meta=(
DeprecationMessage
="abc"))Position:
Meta
Type:
string
Deprecated classes with this metadata will include this text with the standard deprecation warning that Blueprint Scripts generate during compilation.
UCLASS(meta=(
DisplayName
="abc"))Position:
Meta
Type:
string
The name of this node in a Blueprint Script will be replaced with the value provided here, instead of the code-generated name.
UCLASS(meta=(
DontUseGenericSpawnObject
=true))Position:
Meta
Type:
bool
Only used in two places in the engine, on UUserWidget and DragDropOperation. TODO is it bool or flag?
Do not spawn an Object of the class using Generic Create Object node in Blueprint Scripts; this specifier applies only to Blueprint-type classes that are neither Actors nor Actor Components.
UCLASS(Abstract, editinlinenew, BlueprintType, Blueprintable, meta=( DontUseGenericSpawnObject="True", DisableNativeTick) )
class UMG_API UUserWidget : public UWidget, public INamedSlotInterface
UCLASS(meta=(
ExposedAsyncProxy
))Position:
Meta
Type:
flag
Expose a proxy Object of this class in Async Task nodes.
UCLASS(meta=(
KismetHideOverrides
="abc"))Position:
Meta
Type:
string (Comma-separated list)
List of Blueprint events that are not allowed to be overridden.
UCLASS(meta=(KismetHideOverrides="ReceiveAnyDamage,ReceivePointDamage"))
class ENGINE_API ALevelScriptActor : public AActor
UCLASS(meta=(
ProhibitedInterfaces
="abc"))Position:
Meta
Type:
string
Not found any examples of this being used in the engine.
Lists Interfaces that are not compatible with the class.
UCLASS(meta=(
RestrictedToClasses
="abc"))Position:
Meta
Type:
string
Blueprint function library classes can use this to restrict usage to the classes named in the list.
UCLASS(meta=(RestrictedToClasses="BTNode"))
class AIMODULE_API UBTFunctionLibrary : public UBlueprintFunctionLibrary
UCLASS(meta=(
DisplayThumbnail
=true))Position:
Meta
Type:
bool
Related:
UCLASS(BlueprintType, meta = (DisplayThumbnail = "true"))
class PAPER2D_API UPaperFlipbook : public UObject
UCLASS(
Experimental
)Position:
Main
Type:
flag
UCLASS(meta=(
IgnoreClassThumbnail
))Position:
Meta
Type:
flag
UCLASS(meta=(
ExposedAsyncProxy
="abc"))Position:
Meta
Type:
string (Class name without prefix)
UCLASS(Abstract, meta = (ExposedAsyncProxy = AsyncAction))
class GAMEPLAYABILITIES_API UAbilityAsync : public UBlueprintAsyncActionBase
UCLASS(
ScriptName
="abc")Position:
Main
Type:
string
UCLASS(MinimalAPI, meta=(ScriptName="ComposureLibrary"))
class UComposureBlueprintLibrary : public UBlueprintFunctionLibrary
UCLASS(meta=(
CommandLineID
="abc"))Position:
Meta
Type:
string
C++
UCLASS(
CustomConstructor
)Position:
Main
Type:
flag
Prevents automatic generation of the constructor declaration.
UCLASS(
DependsOn
="abc")Position:
Main
Type:
string (comma-separated)
All classes listed will be compiled before this class. The class names provided must indicate classes in the same (or a previous) package. Multiple dependency classes can be identified using a single DependsOn line delimited by commas, or can be specified using a separate DependsOn line for each class. This is important when a class uses a struct or enum declared in another class, as the compiler only knows what is in the classes it has already compiled.
UCLASS(
MinimalAPI
)Position:
Main
Type:
flag
Causes only the class's type information to be exported for use by other modules. The class can be cast to, but the functions of the class cannot be called (with the exception of inline methods). This improves compile times by not exporting everything for classes that do not need all of their functions accessible in other modules.
UCLASS(
Within
="abc")Position:
Main
Type:
string
This is handy for making it clear that a class is designed to be owned by another. Maybe it uses GetOuter so it won't work when created within another class. Commonly used with APlayerController.
Objects of this class cannot exist outside of an instance of an OuterClassName Object. This means that creating an Object of this class requires that an instance of OuterClassName is provided as its Outer Object.
UCLASS(Within=PlayerController)
class ENGINE_API UPlayerInput : public UObject
Editor
UCLASS(
EditInlineNew
)Position:
Main
Type:
flag
Indicates that Objects of this class can be created from the Unreal Editor Property window, as opposed to being referenced from an existing Asset. The default behavior is that only references to existing Objects may be assigned through the Property window). This Specifier is propagated to all child classes; child classes can override this with the NotEditInlineNew Specifier.
UCLASS(
DefaultToInstanced
)Position:
Main
Type:
flag
All instances of this class are considered "instanced". Instanced classes (components) are duplicated upon construction. This Specifier is inherited by subclasses.
Visibility
UCLASS(
ShowFunctions
="abc")This makes more sense when you first understand HideFunctions. I think it works to re-expose functions that were previously hidden using HideFunctions.
Shows all functions within the listed categories in a property viewer.
UCLASS(ShowFunctions=FunctionName)
UCLASS(ShowFunctions=(Category1, Category2))
UCLASS(
HideFunctions
="abc")Say you have a class UCameraComponent, and within it you define a BlueprintCallable function SetFieldOfView. Next, imagine you are creating an orthographic camera class that is a subclass of UCameraComponent. SetFieldOfView no loner makes sense in this new child class, so to hide it you add HideFunctions="SetFieldOfView" to its UCLASS().
According to the documentation you can specify either category names or individual functions.
There is only one example of this being used in the engine, interestingly. Ok maybe it's not that interesting.
Hides all functions in the specified category from the user entirely.
UCLASS()
class UCameraComponent : public USceneComponent
{
UFUNCTION(BlueprintCallable)
virtual void SetFieldOfView(float InFieldOfView);
};
UCLASS(HideFunctions=(SetFieldOfView))
class UOrthographicCameraComponent : public UCameraComponent
{
// ...
};
Actor
UCLASS(
Placeable
)Position:
Main
Type:
flag
I'm pretty sure this is on all AActor subclasses by default. I guess you could specify its opposite NotPlaceable if you wanted a non-placeable actor. See NotPlaceable for use cases.
Indicates that this class can be created in the Editor and placed into a level, UI scene, or Blueprint (depending on the class type). This flag is propagated to all child classes; child classes can override this flag using the NotPlaceable Specifier.
UCLASS(
NotPlaceable
)"This is used in a lot of places in the engine: on test classes, debug actors, gizmos, actors that should only be spawned by other actors."
Negates a Placeable Specifier inherited from a base class. Indicates that Objects of this class may not be placed into a Level, UI scene, or Blueprint in the Editor.
UCLASS(
ComponentWrapperClass
)Position:
Main
Type:
flag
Related:
From what I can tell, this is effectively an alias for IgnoreCategoryKeywordsInSubclasses=true. A class with this specifier will cause the engine to add the IgnoreCategoryKeywordsInSubclasses metadata. This in turn causes all subclasses ignore ShowCategories, HideCategories, AutoExpandCategories, AutoCollapseCategories and PrioritizeCategories.
Seems to be used on minimal-ish Actors that wrap components. For example on ALight that wraps ULightComponent, ASkeletalMeshActor that wraps USkeletalMeshComponent.
Co-occurs with ConversionRoot and ChildCanTick a lot.
Serialization
UCLASS(
Transient
)Objects belonging to this class will never be saved to disk. This is useful in conjunction with certain kinds of native classes which are non-persistent by nature, such as players or windows. This Specifier is propagated to child classes, but can be overridden by the NonTransient Specifier.
UCLASS(
NonTransient
)Negates a Transient Specifier inherited from a base class.
UI
UCLASS(meta=(
DisableNativeTick
))Position:
Meta
Type:
flag
Only used in one place in the engine, on UUserWidget.
UCLASS(Abstract, editinlinenew, BlueprintType, Blueprintable, meta=( DontUseGenericSpawnObject="True", DisableNativeTick) )
class UMG_API UUserWidget : public UWidget, public INamedSlotInterface
UCLASS(meta=(
EntryInterface
="abc"))Position:
Meta
Type:
string (Interface name without leading `I`)
Used to specify the interface that must be implemented by entries to be usable by this list. Only used on UListViewBase and UListView.
/**
* A virtualized list that allows up to thousands of items to be displayed.
*
* An important distinction to keep in mind here is "Item" vs. "Entry"
* The list itself is based on a list of n items, but only creates as many entry widgets as can fit on screen.
* For example, a scrolling ListView of 200 items with 5 currently visible will only have created 5 entry widgets.
*
* To make a widget usable as an entry in a ListView, it must inherit from the IUserObjectListEntry interface.
*/
UCLASS(meta = (EntryInterface = UserObjectListEntry))
class UMG_API UListView : public UListViewBase, public ITypedUMGListView<UObject*>
Internal and Deprecated
UCLASS(
Intrinsic
)Position:
Main
Type:
flag
This indicates that the class was declared directly in C++, and has no boilerplate generated by Unreal Header Tool. Do not use this Specifier on new classes.
UCLASS(
NoExport
)Position:
Main
Type:
flag
Indicates that this class's declaration should not be included in the automatically-generated C++ header file by the header generator. The C++ class declaration must be defined manually in a separate header file. Only valid for native classes. Do not use this for new classes.
UCLASS(meta=(
UsesHierarchy
))Position:
Meta
Type:
flag
The official documentation lists this for both UCLASS and USTRUCT but there are no instances of it being used in the codebase and no code that seems to recognise it. So I think it's maybe legacy or something someone forgot.
Indicates the class uses hierarchical data. Used to instantiate hierarchical editing features in Details panels.
