Interact with behavior graphs via C# scripts

Communication between behavior graphs and C# scripts is key to creating complex and responsive games. While behavior graphs provide a visual method to design complex behaviors, C# scripts provide control and detailed logic implementation.

You can use two techniques to integrate these two systems:

These methods enable GameObjects to share information and react to changes in real time.

Use C# binding to a particular instance of BehaviorGraphAgent

You can bind directly to a BehaviorGraphAgent to subscribe to BlackboardVariable using the BehaviorGraphReference API.

You can then subscribe to the BlackboardVariable.OnValueChanged event or in case of an Event Channel, subscribe to BlackboardVariable.Value.Event event.

Example code

[SerializeField] private BehaviorGraphAgent m_Agent;

// Agent state has changed to [value] (where value is of type StateExample)
private BlackboardVariable<StateEventChannel> m_stateEventChannelBBV;
private BlackboardVariable<StateExample> m_stateBBV;

private void OnEnable()
{
    if (m_Agent.BlackboardReference.GetVariable("StateEventChannel", out m_stateEventChannelBBV))
        m_stateEventChannelBBV.Value.Event += OnStateEvent;

    if (m_Agent.BlackboardReference.GetVariable("StateToReact", out m_stateBBV))
        m_stateBBV.OnValueChanged += OnStateValueChanged;
}

private void OnDisable()
{
    if (m_stateEventChannelBBV != null)
        m_stateEventChannelBBV.OnValueChanged -= OnStateChanged;
    if (m_stateBBV != null)
        m_stateBBV.OnValueChanged -= OnStateValueChanged;
}

private void Update()
{
    // your custom logic

    // Send event to the event channel of the referenced agent.
    // Only this instance of agent will receive it (except if the BlackboardVariable is 'Shared').
    m_stateEventChannelBBV.Value.SendEventMessage(StateExample.Alert);
}

private void OnStateEvent(StateExample value)
{
    // React to event
}

private void OnStateValueChanged()
{
    // React to state change
}

C# binding using Event Channel asset

Event Channel assets allow for global communication across multiple behavior graphs or between graphs and C# components. You can generate an instance of an Event Channel to send and receive messages. This method is ideal when you need consistent event handling across systems.

Perform the following steps:

  1. Create the Event Channel.

    1. Open the Project window.
    2. Right-click and select Create > Behavior > Event Channel > [Channel Name].

    This creates an instance of that Event Channel that you can assign to the behavior graph and C# components.

  2. To assign the Event Channel, in the C# component, use the Event Channel API to listen or send a new message.

Example code

[SerializeField] private StateEventChannel m_EventChannel;

private void OnEnable()
{
    m_EventChannel.Event += OnStateEvent;
}
private void OnDisable()
{
    m_EventChannel.Event -= OnStateEvent;
}

private void Update()
{
    // your custom logic

    // Send event to the event channel instance.
    // All graphs and C# systems on that same event channel instance will receive it.
    m_EventChannel.SendEventMessage(StateExample.Alert);
}

private void OnStateEvent(StateExample value)
{
    // React to event
}

Additional resources