# Blackboard Note

## Blackboard Notes

{% hint style="warning" %}
To receive updates from a Blackboard Note or a Blackboard Event, a script must implement `IFollowBlackboard`, or [inherit from `BlackboardFollower`](/magic-pig-games/game-modules-4/module-documentation/blackboard/blackboard-follower.md).
{% endhint %}

**Blackboard Notes** contain a "Topic" and "Subject", both strings, which are similar to the key in a Dictionary key/value pair. They also contain a selection of data types, including Game Module types like GameItemObject or GameStat.

The Blackboard module allows other objects to follow it, and receive a notification whenever a `BlackboardNote` is added or updated, and when a `BlackboardEvent` is sent. Followers should check to see if the topic and subject are what they are looking for, and if so, handle the new data.

<pre class="language-csharp" data-overflow="wrap"><code class="lang-csharp"><strong>// BlackboardNote.cs
</strong><strong>public string name; // Mostly useful for the inspector
</strong>public string topic; // The broad topic. Examples could be "Kills" or "Dungeon Doors"
public string subject; // The specific subject. Such as "Goblins" or "Crypt" 
public object value;

// General types
public float valueFloat; 
public int valueInt;
public string valueString; 
public bool valueBool;
public GameObject valueGameObject;
        
// Game Module types
public GameStat valueGameStat;
public GameItemObject valueGameItemObject;
public GameItemAttribute valueGameItemAttribute;
public GameCondition valueGameCondition;
public GameQuest valueGameQuest;
public GameLootBox valueGameLootBox;
        
// Game Lists
public GameStatList valueGameStatList;
public GameItemObjectList valueGameItemObjectList;
public GameConditionList valueGameConditionList;
public GameQuestList valueGameQuestList;
</code></pre>

You can `Add()` Blackboard Notes, though it may be more ideal to Update() the note in most cases, as this will automtically add the note if it does not yet exist.

```csharp
// Update a note value, or add it if it doesn't exist
blackboard.UpdateNote("Party", "Distance Travelled", DistanceTravelled, true, true);

// Update a note without sending a notification to followers
blackboard.UpdateNote("Party", "Distance Travelled", DistanceTravelled, true, false);

// Get a note from the Blackboard
blackboard.TryGet(topic, subject, out BlackboardNote note);
Debug.Log($"The int value is {note.valueInt}.");

// Example of receiving a change from the blackboard
public override void ReceiveChange(BlackboardNote blackboardNote)
{
     // We only care about our topic / subject
     if (blackboardNote.topic != topicWeCareAbout 
          || blackboardNote.subject != subjectWeCareAbout) return;

     DoSomethingWith(blackboardNote);
}
```


---

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