Behavior Public API

Pro Behavior

This page documents the supported public API for the Behavior System.

The Behavior System public API is intentionally small. Use it to execute behavior libraries and to add project-specific behavior functions. Editor widgets, outliner rows, details customizations, drag-drop operations, binding internals, operator internals, registry mutation functions, and evaluator internals are implementation details.

Some reflected types are visible from public headers because Unreal assets and UHT need them. Visibility does not make them a stable extension point.

Supported Entry Points

Area	Supported entry point	Use for
Behavior Library assets	`UJ2TagBehaviorLibraryAsset`	Storing behavior sections, rules, actions, overrides, and execution settings.
Behavior execution helpers	`UJ2TagBehaviorBlueprintLibrary`	Executing behaviors, creating behavior contexts, and reading event context in Blueprint.
TagSet behavior mappings	`UJ2TagSetAsset` behavior resolver functions	Reading behavior mappings from TagSets, groups, and tags.
Blueprint behavior functions	Blueprint classes derived from `UJ2TagBehaviorBlueprintLibrary`	Custom Blueprint expressions and actions.
C++ behavior functions	Native classes derived from `UJ2TagBehaviorFunctionLibraryBase`	Custom native expressions and actions.

Behavior Library Assets

Class:

UJ2TagBehaviorLibraryAsset

Behavior Library assets are authored in the Behavior Editor and referenced by TagSets, groups, and tags.

Important data areas:

Area	Purpose
`ActionGroups`	Primary behavior structure made of rules and actions.
`Steps`	Compatibility list for older linear workflows.
`ThemeColors`	Colors for cards and visualization.
`SourceEvent`	Event that triggers the behavior.
`Priority`	Lower values execute earlier.
`bEnabled`	Enables or disables the behavior.
`DebugLogMode`	Execution logging mode.

Execution Helpers

Class:

UJ2TagBehaviorBlueprintLibrary

Use this class as the Blueprint utility API for behavior execution and context helpers.

Typical utility API:

ExecuteBehavior
TriggerBehaviorEvent
MakeBehaviorContext
SetContextString, SetContextBool, SetContextInt, SetContextFloat, SetContextObject, SetContextClass
GetEventActor, GetEventComponent, GetEventTagName, GetEventSourceObject
GetRegisteredFunctionCount, GetAvailableFunctions, GetFunctionCategories

TagSet Behavior Mappings

Class:

UJ2TagSetAsset

TagSet assets can provide Behavior Library mappings at the TagSet, group, and tag level. Use the resolver functions when project code needs to inspect the effective behavior setup.

Important behavior resolver functions:

ResolveTagSetBehaviors
ResolveTagSetBehaviorSections
ResolveGroupPolicies
ResolveGroupBehaviorSections
ResolveTagBehaviors
ResolveTagBehaviorSections

Custom Behavior Functions

Custom behavior functions are the supported extension point for project-specific Behavior System logic.

Authoring mode	Required base class	Result
Blueprint	`UJ2TagBehaviorBlueprintLibrary`	Custom Blueprint functions become Behavior expressions or actions.
C++	`UJ2TagBehaviorFunctionLibraryBase`	Custom native functions become Behavior expressions or actions.

The behavior registry accepts functions only from:

UJ2TagBehaviorBlueprintLibrary Blueprint classes
UJ2TagBehaviorFunctionLibraryBase native classes
the built-in UJ2TagBehaviorFunctionLibrary

Class names alone are not enough. A class named MyBehaviorFunctionLibrary is ignored unless it derives from the supported base class.

Blueprint Function Libraries

Create a J2 Tag Behavior Function Library asset and add functions to it.

Rules:

pure Blueprint functions are shown as expressions
non-pure callable Blueprint functions are shown as actions
input pins become behavior inputs
output pins and return values become behavior outputs
hidden World Context pins are provided automatically
function names and pin names should be treated as serialized API

C++ Function Libraries

Derive from UJ2TagBehaviorFunctionLibraryBase:

#pragma once

#include "Behavior/J2TagBehaviorFunctionLibraryBase.h"
#include "MyBehaviorFunctions.generated.h"

UCLASS()
class UMyBehaviorFunctions : public UJ2TagBehaviorFunctionLibraryBase
{
    GENERATED_BODY()

public:
    UFUNCTION(BlueprintPure, Category = "Project|Validation")
    static void HasRequiredPrefix(FName Tag, FName Prefix, bool& Result);

    UFUNCTION(BlueprintCallable, Category = "Project|Validation")
    static void WriteValidationMessage(UObject* TargetObject, const FString& Message, bool& Result);
};

Example implementation:

void UMyBehaviorFunctions::HasRequiredPrefix(FName Tag, FName Prefix, bool& Result)
{
    Result = Tag.ToString().StartsWith(Prefix.ToString());
}

void UMyBehaviorFunctions::WriteValidationMessage(UObject* TargetObject, const FString& Message, bool& Result)
{
    Result = IsValid(TargetObject) && !Message.IsEmpty();
}

Recommended parameter patterns:

use reflected Unreal types such as bool, int32, float, double, FString, FName, FText, FVector, FRotator, FTransform, FGameplayTag, UObject*, and TSubclassOf<UObject>
use output reference parameters such as bool& Result, int32& Count, or a typed output name
keep categories and tooltips descriptive because the Behavior Editor displays reflected metadata
prefer Result for the primary output when the function returns a condition or success state

Avoid:

maps, sets, delegates, interfaces, latent functions, and unsupported reflected parameter types
direct access to Behavior Editor widgets, panels, outliner nodes, or customization classes
directly registering or mutating functions through the behavior registry from project code
renaming functions, owner classes, input pins, output pins, or override paths after assets use them