Description

UPROPERTY variables are declared using standard C++ syntax with additional descriptors, such as variable specifiers and metadata placed above the declaration.

UPROPERTY([specifier,specifier,...],[meta=(key=value,key=value,...)])
TypeVariableName;

Aside from this comprehensive wiki article, the official documentation lists all valid property specifiers excluding the meta data specifiers below.

Garbage Collection

In a nutshell, Garbage Collection (GC) traverses the object hierarchy through designated UPROPERTYs, starting from the root objects (hence AddToRoot and RemoveFromRoot methods). Any object that cannot be reached through this traversal will be garbage collected. Accordingly, non-UPROPERTY variables are not counted by the GC system.

In other words, if you have two UObjects which reference each other (aka. Cyclic Reference), but no other objects refer to them, both of these UObjects will be GCed.

Valid Specifiers

• Const

  This property is const and should be exported as const.

• Config

  Property should be loaded/saved to ini file as permanent profile.

• GlobalConfig

  Same as above but load config from base class, not subclass.

• Localized

  Property should be loaded as localizable text. Implies ReadOnly.

• Transient

  Property is transient: shouldn't be saved, zero-filled at load time. Opposite of the SaveGame specifier.

• DuplicateTransient

  Property should always be reset to the default value during any type of duplication (copy/paste, binary duplication, etc.)

• NonPIETransient

  Property should always be reset to the default value during any type of duplication (copy/paste, binary duplication, etc.)

• Ref

  Value is copied out after function call. Only valid on function param declaration.

• NoClear

  Hide clear (and browse) button in the editor.

• EditFixedSize

  Indicates that elements of an array can be modified in Editor, but its size cannot be changed.

• Replicated

  Property is relevant to network replication.

• ReplicatedUsing

  Property will be configured for replication. The provided function is called only when the replicated property is received via replication.

• RepRetry

  Retry replication of this property if it fails to be fully sent (e.g. object references not yet available to serialize over the network)

• NotReplicated

  Skip replication (only for struct members and parameters in service request functions).

• Interp

  Interpolatable property for use with matinee. Always user-settable in the editor.

• NonTransactional

  Changes to this variable value will not be included in the editor's undo/redo history.

• Instanced

  Property is a component reference. Implies EditInline and Export.

• BlueprintAssignable

  MC Delegates only. Property should be exposed for assigning in blueprints.

• Category

  Specifies the category of the property within the Editor. Supports sub-categories separated by "|".

• SimpleDisplay

  Properties appear visible by default in a details panel

• AdvancedDisplay

  Moves the property into the Advanced dropdown in the Details panel within the Editor.

• EditAnywhere

  Indicates that this property can be edited via property windows, archetypes and instances within the Editor.

• EditInstanceOnly

  Indicates that this property can be edited by property windows, but only on instances, not on archetypes

• EditDefaultsOnly

  Indicates that this property can be edited by property windows, but only on archetypes. This operator is incompatible with the Visible* specifiers.

• VisibleAnywhere

  Indicates that this property is visible in property windows, but cannot be edited at all

• VisibleInstanceOnly

  Indicates that this property is only visible in property windows for instances, not for archetypes, and cannot be edited

• VisibleDefaultsOnly

  Indicates that this property is only visible in property windows for archetypes, and cannot be edited

• BlueprintReadOnly

  This property can be read by blueprints, but not modified.

• BlueprintReadWrite

  This property can be read or written from a blueprint.

• AssetRegistrySearchable

  The AssetRegistrySearchable keyword indicates that this property and it's value will be automatically added to the asset registry for any asset class instances containing this as a member variable. It is not legal to use on struct properties or parameters.

• SaveGame

  Property should be serialized for save game. Opposite of the Transient specifier.

• BlueprintCallable

  Multicast Delegates only. Property should be exposed for calling in blueprint code

• BlueprintAuthorityOnly

  MC Delegates only. This delegate accepts (only in blueprint) only events with BlueprintAuthorityOnly.

• TextExportTransient

  Property shouldn't be exported to text format (e.g. copy/paste)

• BindWidget

  Allows C++ code to access widgets of a Blueprint subclass at runtime. This meta specifier only works on subclasses of UWidget.

  Example usage:

  UPROPERTY(BlueprintReadWrite, meta = (BindWidget))
  UTextBlock* CoinLabel;
  

  Create a User Widget Blueprint subclass of your C++ widget and create a widget of the same name and type. You can now access and modify that widget from C++.

• BindWidgetOptional

  If a bound widget with this meta specifier is not found in a User Widget Blueprint, only a log entry will be displayed instead of an error being thrown during compilation.

• BindWidgetAnim

  Same concept as BindWidget, but for UWidgetAnimations.

• BindWidgetAnimOptional

  Similar to BindWidgetOptional, no error will be thrown if no animation is found in the User Widget Blueprint.

Valid Meta Properties

• DisplayName

  Sets the display name for the property in the editor. The default value is the variable name with a space before each capital letter beyond the first. For example MyVariableName would display as My Variable Name.

• AllowAbstract

  Used for FStringClassReference properties. Indicates whether abstract class types should be shown in the class picker.

• AllowedClasses

  Used for FStringAssetReference properties. Comma delimited list that indicates the class type(s) of assets to be displayed in the asset picker.

• AllowPreserveRatio

  Used for FVector properties. It causes a ratio lock to be added when displaying this property in details panels.

• ArrayClamp

  Used for integer properties. Clamps the valid values that can be entered in the Details to be between 0 and the maximum index of an array. However, if you change its value not in Details, it can exceed the limit value.

• ClampMin

  Used for float and int properties. Specifies the minimum value that may be entered for the property.

• ClampMax

  Used for float and int properties. Specifies the maximum value that may be entered for the property.

• DisplayThumbnail

  Indicates that the property is an asset type and it should display the thumbnail of the selected asset.

• EditCondition

  Specifies a boolean property that is used to indicate whether editing of this property is allowed within the editor.

• ExactClass

  Used for FStringAssetReference properties in conjunction with AllowedClasses. Indicates whether only the exact classes specified in AllowedClasses can be used or whether subclasses are valid.

• ExposeFunctionCategories

  From the official documentation: "Specifies a list of categories whose functions should be exposed when building a function list in the Blueprint Editor."

• ExposeOnSpawn

  Specifies whether the property should be exposed on a Spawn Actor for the class type.

• FixedIncrement

  From the official documentation: "Deprecated."

• ForceRebuildProperty

  [Undocumented]

• HideAlphaChannel

  Used for FColor and FLinearColor properties. Indicates that the Alpha property should be hidden when displaying the property widget in the details.

• IsBlueprintBaseOnly

  Used for FStringClassReference properties. Indicates whether only blueprint classes should be shown in the class picker.

• OnlyPlaceable

  Used for Subclass properties. Indicates whether only placeable classes should be shown in the class picker.

• MakeEditWidget

  When used with certain objects such as an FVector, you get to use an "edit widget" within the editor to transform the object in space.

• MakeStructureDefaultValue

  For properties in a structure indicates the default value of the property in a blueprint make structure node.

• MetaClass

  Used FStringClassReference properties. Indicates the parent class that the class picker will use when filtering which classes to display.

• Multiple

  From the official documentation: "Used for numeric properties. Stipulates that the value must be a multiple of the metadata value."

• MultiLine

  Used for FString and FText properties. Indicates that the edit field should be multi-line, allowing entry of newlines.

  Usage: meta=(MultiLine=true)

• NoElementDuplicate

  Used for array properties. Indicates that the duplicate icon should not be shown for entries of this array in the property panel.

• NoSpinbox

  Used for float and int properties. Indicates that the spin box element of the number editing widget should not be displayed.

• FilePathFilter

  Used by FFilePath properties. Indicates the path filter to display in the file picker.

• RelativePath

  Used by FDirectoryPath properties.

• RelativeToGameContentDir

  Used by FDirectoryPath properties.

• ShowOnlyInnerProperties

  Used for struct properties. The properties of the struct are shown directly in the details panel instead of having the need to expand them to show them.

• SliderExponent

  From the official documentation: "Used by numeric properties. Indicates how rapidly the value will grow when moving an unbounded slider."

• UIMin

  Used for float and int properties. Specifies the lowest that the value slider should represent.

• UIMax

  Used for float and int properties. Specifies the highest that the value slider should represent.

Deprecation

Native: Add the _DEPRECATED suffix to the end of the variable name.

Blueprint: You may deprecate a Blueprint Property using a checkbox in its properties.

Related

Here is a great list of all UPROPERTY specifiers.

UCLASS, UFUNCTION, USTRUCT, UPARAM, UENUM, UDELEGATE