Learn how to use NodeCanvas

Using Task Attributes

To make life easier and things faster, both Action and Condition Tasks can make use of some attributes for both runtime as well as editor convenience. More specifically:

Runtime Attributes


Update Note: [AgentType] attribute has been deprecated as of v2.7.0. You should now instead, use the generic version of tasks ( MyAction<NavMeshAgent> ), to specify the AgentType directly. The generic argument can also be of interface types as well. Thus, now the .agent property is already of that generic type and without any casting required. The following information shown here still applies the same but instead of using an attribute, usage of the generic versions of Tasks is required.

You can use this attribute on the Action or Condition Task class. This specifies the Component type which is required for the agent game object to have. If no such Component exists, the Task Initialization will fail. If such a Component exists, then the agent property explained earlier, is certain to be of that type, so for example you can cast it if you want. If you don’t care for a specific type of Component, simply do not use this attribute.

Using this attribute will also show the agent field inspector which allows you to override the agent to be used. There are three options for which agent is going to perform the Task as follows.

  • The owner agent (self), which is the default agent propagated to the Task on execution.
  • An override agent reference which is directly assigned.
  • An override agent selected from a blackboard variable.

[EventReceiver(params string[])]

Update Note: [EventReceiver] is deprecated as of v3.0.0. To utilize Unity events, you now have to make use of the ‘.router’ property. The ‘.router’ property returns an EventRouter through which you can subscribe and unsubscribe to (normal c#) events that the EventRouter has. For ActionTasks this is best done in ‘OnExecute’/’OnStop’. For ConditionTasks this is best done in ‘OnEnable’/’OnDisable’.

Use this attribute also on the Task class if you want to use Unity’s messages like OnTriggerEnter, OnTriggerExit etc. Specify The messages you want to listen to and then you can use them in the task as you normally would. Here are the event messages that can be listened and used right now:

  • OnTriggerEnter
  • OnTriggerExit
  • OnTriggerStay
  • OnCollisionEnter
  • OnCollisionExit
  • OnCollisionStay
  • OnTriggerEnter2D
  • OnTriggerExit2D
  • OnTriggerStay2D
  • OnCollisionEnter2D
  • OnCollisionExit2D
  • OnCollisionStay2D
  • OnMouseDown
  • OnMouseDrag
  • OnMouseEnter
  • OnMouseExit
  • OnMouseOver
  • OnMouseUp
  • OnBecameVisible
  • OnBecameInvisible
  • OnAnimatorIK
  • OnEnable
  • OnDisable

Note: There already exist Condition Tasks for triggers, collisions, and mouse events.

Use this attribute over a Component type field. Whenever a new agent is set (OnInit of the Task), the field will be set by using GetComponent from the agent. If no such component exists, the Task Initialization will fail. This is a helper attribute to save you from doing this manually.

Use this over a nullable public field to make it show red if it is indeed null or empty string in case of a string. Furthermore, if such a field is null when the Task gets executed the Initialization will fail. This saves you from doing null checks all the time.

Design Attributes

All public fields of both Action and Condition Tasks will show within the NodeCanvas Editor Inspector for all inspectable types. There are also some attributes you can use to customize the shown controls as follows.

[Header(string title)]
Use over a field to show a header with ‘title’ above it.

[SliderField(float min, float max)]
Use over a float/int field to show a slider instead.

[MinValue(float or int min]
Use over a field to disallow float/int values less than ‘min’.

[TextAreaField(float height)]
Use over a string field to show it as a text area control instead.

Use over a string field to show a TagField control instead.

Use over an int field to show a LayerField control instead.

[ShowIf(string fieldName, int checkValue)]
Use over a field to only show it if the specified field (by name) is equal to the ‘checkValue’.

[ShowButton(string buttonTitle, string methodNameCall)]
Use over a field to show a button in the inspector with ‘buttonTitle’ that when clicked a method named ‘methodNameCall’ will be called (it needs to have no parameters).

[Callback(string methodName)]
Use over a field to call a method named ‘methodName’ whenever the field changes in the inspector.

Note: All attributes also work the same on BBParameter<T> fields, meaning you can use the [Slider] attribute for example on a BBParameter<int> field the same.
Note: If you really need a very special editor you can override the virtual protected void OnTaskInspectorGUI() and wrap it within an #if UNITY_EDITOR


Use this on the Task class to specify a category to be shown in. Note that you can use subcategories by using “/”

If your class name is too weird for some reason or you just want it to show by a specific name, use this attribute over the Task class.

Using this attribute will allow you to provide a help description that can be read within the inspector of the task.

To specify the information shown when assigned on a node, you will have to override the ‘virtual string info’ property and return the string you would like to show, meaning what the Task is going to finally do or check. This is very useful for getting a good overview of what will happen directly when looking at the behaviour in the editor. If the property is not overridden then the Task name will simply show instead.

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