UPROPERTY

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, ...)])
 Type VariableName;

Garbage Collection

Any Object that has at least one valid pointer stored inside a UPROPERTY will not be Garbage Collected (GC). Non-UPROPERTY variables will not be counted by the GC system.

Valid Specifiers

Note Pro Tip: You can use using namespace UP; to have these keywords as enums thus potentially have them auto-complete.
Works with VAssistX

Note Pro Tip: All valid UPROPERTY specifiers are listed as enum values in "ObjectBase.h", Line 728

Const

This property is const and should be exported as const.

Note As of at least 4.12.5, using this as a UPROPERTY specifier will cause a compilation error. Use one of the Visible* specifiers instead.

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.

Note This is a UPARAM specifier; not a UPROPERTY specifier.

Export

Object property can be exported with it's owner.

EditInline

Edit this object reference inline in the editor.

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.

Note Static arrays of containers, such as TArray, are not allowed. Use dynamic arrays.

Note May not work properly with container arrays of Structs. Mine were not editable. 4.12.5

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.

Example UPROPERTY(ReplicatedUsing = OnRep_ReplicatedVar)
int32 ReplicatedVar;

void OnRep_ReplicatedVar();

//or

void OnRep_ReplicatedVar(int32 OldValue);

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 "|".

Example UPROPERTY(Category = "CategoryName")

UPROPERTY(Category = "Category|SubCategory")

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.

Note Does not appear to work within property subcategories as of 4.12.5

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)

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'.

Example UPROPERTY(meta = (DisplayName = "My Display Name"))

Note Boolean variables with names that start with a lowercase "b" will be culled by default within the Editor

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 UI to be between 0 and the length of the array specified.

ClampMin

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

Example UPROPERTY(meta = (ClampMin = 0)
int32 Clamp;

Note Does not work with containers, such as TArray<float>

ClampMax

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

Example UPROPERTY(meta = (ClampMax = 10.5)
float Clamp;

Note Does not work with containers, such as TArray<float>

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.

Example UPROPERTY(BlueprintReadWrite, EditAnywhere)
bool bAllowEdit;

UPROPERTY(BlueprintReadWrite, EditAnywhere, meta = (EditCondition = bAllowEdit))
int32 EditMe;

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

[Undocumented]

ExposeOnSpawn

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

Example UPROPERTY(BlueprintReadWrite, meta = (ExposeOnSpawn)

FixedIncrement

[Undocumented]

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

[Undocumented]

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 integer and float 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

[Undocumented]

UIMin

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

UIMax

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

Related

UCLASS, UFUNCTION, USTRUCT, UMETA, UPARAM, UENUM, UDELEGATE