Best practice for required references

Unity Engine
1

Hi,

I write a lot of scripts like this:

public class MyScript : MonoBehaviour
{
    public Transform VeryImportantReference;

    private void Start()
    {
        if (VeryImportantReference == null)
        {
            Debug.LogError("VeryImportantReference not set.");
            enabled = false // avoid log spam
        }
       
    }
   
    private void Update()
    {
        // use the reference here...
    }
}

Is there a best practice of this scenario or even a RequireField attribute like RequireComponent. This checks are very repetitive and annoying…

2

No, there isn’t one.

You can make one.

Easiest way is to just write an ‘assert’ function:

public static class Assert
{

    public static bool ReferenceExists(UnityEngine.Object obj, string name)
    {
        if(obj == null)
        {
            Debug.LogError(name + " not set");
            return false;
        }
        else
        {
            return true;
        }
    }

}

public class MyScript : MonoBehaviour
{

    public Transform VeryImportantReference;

    void Start()
    {
        this.enabled = Assert.ReferenceExists(VeryImportantReference, "VeryImportantReference");
    }

}
3

Unity has its own Assert class so you don’t even have to write your own :slight_smile:

1 Like
4

Nice, is that new?

5

New in 5 I think. Not sure which minor version.

6

Nice, that goes in the right direction. Maybe I can create something, that gives a visual feedback in the editor, like a (Property xyz not set warning)… A attribute or something like that.

7

You can also do that in the OnValidate MonoBehaviour message to make sure your references are assigned at edit time instead of doing in Start.

8

I’ve created a simple attribute and property drawer:

Attribute:

public class RequiredAttribute : PropertyAttribute
{
}

Drawer:

[CustomPropertyDrawer(typeof(RequiredAttribute))]
public class RequiredDrawer : PropertyDrawer
{
    private const float HELPBOX_HEIGHT = 38.0f;
    private const float TOP_MARGIN = 2.0f;

    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        float propHeight = EditorGUI.GetPropertyHeight(property, label);
        position.height = propHeight;

        EditorGUI.PropertyField(position, property, label);

        if (property.objectReferenceValue == null)
        {
            position.y += position.height + TOP_MARGIN;
            position.height = HELPBOX_HEIGHT;
            EditorGUI.HelpBox(position, string.Format("{0} is required!", label.text), MessageType.Error);
        }
    }

    public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
    {
        float height = EditorGUI.GetPropertyHeight(property, label);
        if (property.objectReferenceValue == null)
        {
            height += HELPBOX_HEIGHT + TOP_MARGIN;
        }

        return height;
    }
}

Now, you will get an error in the inspector, if the property with the require attribute has a null reference.
This isn’t perfect because if you collapse the component, there will be no reminder, that you have to set this property before you should press play.

2 Likes