> For the complete documentation index, see [llms.txt](https://blackboard.crashkonijn.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://blackboard.crashkonijn.com/examples/09_object_lists.md).

# 09 Object Lists

This example shows you how to use object lists in a blackboard.

These files can be found in the /Examples/\[example] and /Blackboards/Examples folders.

![Example 09 Object Lists editor](/files/OfFelNHzMgrkmewAccq7)

## ObjectListBlackboard.cs

```csharp
using System;
using System.Collections.Generic;
using System.Linq;
using CrashKonijn.RabbitBlackboard.Contracts;

namespace CrashKonijn.BlackboardPro.Blackboards.Examples
{
    [Serializable]
    public class SerializedChange
    {
        public int amount;
    }

    [Serializable]
    public partial class SignalChange : ISomeAreSignals
    {
        [Signal]
        private int amount;

        [Signal]
        private string name;
    }

    public partial class ObjectListBlackboard : BlackboardBehaviour
    {
        private int startHealth = 100;

        // Lists can be of any type
        private List<SerializedChange> serializedChanges;
        private List<SignalChange> signalChanges;

        // This is a computed property, showing health being equal to startHealth plus the sum of all changes.
        private static int serializedHealth(Signals.StartHealth startHealth, Signals.SerializedChanges changes) => startHealth.Value + changes.Value.Sum(x => x.amount);

        // WARNING: even though the type here has signals on its own. Change events are triggered by the VALUE of the signal.
        // This means that even when changing the amount of a SignalChange, the containing list won't trigger an event.
        private static int signalHealth(Signals.StartHealth startHealth, Signals.SignalChanges changes) => startHealth.Value + changes.Value.Sum(x => x.Amount);
    }
}

```

## ObjectListsHealthBehaviour.cs

```csharp
using CrashKonijn.BlackboardPro.Blackboards.Examples;
using CrashKonijn.RabbitBlackboard.Contracts;
using UnityEngine;
using ObjectListBlackboard = CrashKonijn.BlackboardPro.Blackboards.Examples.ObjectListBlackboard;
using SignalChange = CrashKonijn.BlackboardPro.Blackboards.Examples.SignalChange;

namespace CrashKonijn.BlackboardPro.Examples._09_object_lists
{
    [RequireComponent(typeof(ObjectListBlackboard))]
    public class ObjectListsHealthBehaviour : MonoBehaviour
    {
        /* Simple hack to show a button in the editor */
        [Header("Removes 10 health.")]
        [Button(nameof(DoDamage))]
        public string doDamageButton;

        /* Simple hack to show a button in the editor */
        [Header("Adds 10 health")]
        [Button(nameof(Heal))]
        public string healButton;

        /* Simple hack to show a button in the editor */
        [Header("Clears the changes list")]
        [Button(nameof(Clear))]
        public string clearButton;

        private ObjectListBlackboard blackboard;

        public ObjectListBlackboard Blackboard
        {
            get
            {
                if (this.blackboard == null)
                {
                    this.blackboard = this.GetComponent<ObjectListBlackboard>();
                }

                return this.blackboard;
            }
        }

        public void DoDamage()
        {
            this.Blackboard.SignalChanges.Add(new SignalChange
            {
                Amount = -10,
            });
            this.Blackboard.SerializedChanges.Add(new SerializedChange
            {
                amount = -10,
            });
        }

        public void Heal()
        {
            this.Blackboard.SignalChanges.Add(new SignalChange
            {
                Amount = 10,
            });
            this.Blackboard.SerializedChanges.Add(new SerializedChange
            {
                amount = 10,
            });
        }

        public void Clear()
        {
            this.Blackboard.SignalChanges.Clear();
        }
    }
}

```


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