How to set SerializedProperty.propertyType in a CustomPropertyDrawer

Question

I am using these two libraries:

• Unity-SerializableDictionary: https://github.com/starikcetin/Unity-SerializableDictionary

• Unity Scene Reference: https://github.com/starikcetin/unity-scene-reference

Basically, the serializable dictionary looks at the propertyType to determine if the property can be expanded or not, with the following check:

static bool CanPropertyBeExpanded(SerializedProperty property)
{
    switch(property.propertyType)
    {
    case SerializedPropertyType.Generic:
    case SerializedPropertyType.Vector4:
    case SerializedPropertyType.Quaternion:
        return true;
    default:
        return false;
    }
}

However, it appears that Scene Reference is registered as an expandable property even though it isn't. This is because -apparently- Unity registers it as of type Generic.

I can solve this simply by setting the SerializedProperty.propertyType to a more meaningful type, but it is read-only.

So, how can I set the SerializedProperty.propertyType of a custom property drawer?

Answer 1

It isn't documented but the type Generic is automatically assigned for any custom class (like e.g. SceneReference). You can NOT change the propertyType since it is read-only ... and you can't tell the compiler to handle your custom class as something else ...

Even if you could ... what would be a "more meaningful type"? The available types for SerializedPropertyType are limited and none of them is more meaningful for a custom class.

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The main "issue" here is:

The SerializableDictionary drawer simply assumes that usually if you have a custom (Generic) class without a custom PropertyDrawer - so using the default drawer - it behaves exactly like the default drawer of Quaternion or Vector4:

• It has a label and foldout in the first line
• fields/content are/is drawn below and only if the property is folded out

Since the drawer for SceneReference doesn't implement this behavior it is drawn on top of the dictionary's key-field.

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So as simplest fix of course you can simply remove the

case SerializedPropertyType.Generic:

so the SceneAsset (and all other custom classes) is treated like a normal unfolded field - a matter of taste

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Alternatively what you could do about it is change the PropertyDrawer of SceneReference to reflect the behavior of e.g. Quaternion:

• Add an EditorGUI.Foldout with the label which changes the property.isExpaned value
• Move any content one line below (and optionally intended)
• Add one line to the property height and a condition for if(!property.isExpanded)

Might look e.g. like:

// Made these two const btw
private const float PAD_SIZE = 2f;
private const float FOOTER_HEIGHT = 10f;

public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
{
    // Move this up
    EditorGUI.BeginProperty(position, GUIContent.none, property);
    {
        // Here we add the foldout using a single line height, the label and change
        // the value of property.isExpanded
        property.isExpanded = EditorGUI.Foldout(new Rect(position.x, position.y, position.width, lineHeight), property.isExpanded, label);

        // Now you want to draw the content only if you unfold this property
        if (property.isExpanded)
        {
            // Optional: Indent the content
            //EditorGUI.indentLevel++;
            //{

            // reduce the height by one line and move the content one line below
            position.height -= lineHeight;
            position.y += lineHeight;

            var sceneAssetProperty = GetSceneAssetProperty(property);

            // Draw the Box Background
            position.height -= FOOTER_HEIGHT;
            GUI.Box(EditorGUI.IndentedRect(position), GUIContent.none, EditorStyles.helpBox);
            position = boxPadding.Remove(position);
            position.height = lineHeight;

            // Draw the main Object field
            label.tooltip = "The actual Scene Asset reference.\nOn serialize this is also stored as the asset's path.";


            var sceneControlID = GUIUtility.GetControlID(FocusType.Passive);
            EditorGUI.BeginChangeCheck();
            {
                // removed the label here since we already have it in the foldout before
                sceneAssetProperty.objectReferenceValue = EditorGUI.ObjectField(position, sceneAssetProperty.objectReferenceValue, typeof(SceneAsset), false);
            }
            var buildScene = BuildUtils.GetBuildScene(sceneAssetProperty.objectReferenceValue);
            if (EditorGUI.EndChangeCheck())
            {
                // If no valid scene asset was selected, reset the stored path accordingly
                if (buildScene.scene == null) GetScenePathProperty(property).stringValue = string.Empty;
            }

            position.y += paddedLine;

            if (!buildScene.assetGUID.Empty())
            {
                // Draw the Build Settings Info of the selected Scene
                DrawSceneInfoGUI(position, buildScene, sceneControlID + 1);
            }

            // Optional: If enabled before reset the indentlevel
            //}
            //EditorGUI.indentLevel--;
        }
    }
    EditorGUI.EndProperty();
}

public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
{
    var sceneAssetProperty = GetSceneAssetProperty(property);
    // Add an additional line and check if property.isExpanded
    var lines = property.isExpanded ? sceneAssetProperty.objectReferenceValue != null ? 3 : 2 : 1;
    // If this oneliner is confusing you - it does the same as
    //var line = 3; // Fully expanded and with info
    //if(sceneAssetProperty.objectReferenceValue == null) line = 2;
    //if(!property.isExpanded) line = 1;

    return boxPadding.vertical + lineHeight * lines + PAD_SIZE * (lines - 1) + FOOTER_HEIGHT;
}

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Now it looks like e.g.

[Serializable]
public class TestDict : SerializableDictionary<string, SceneReference> { }

public class Example : MonoBehaviour
{
    public SceneReference NormalReference;

    public TestDict DictExample = new TestDict();
}

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