特定の種類(拡張子)のファイルだけを設定したい

Example.cs

using UnityEngine;

public class Example : MonoBehaviour
{
    [SerializeField, FilterFileExtension ("unity")]
    private Object[] sceneFileList = new Object[] {};
}

FilterFileExtensionAttribute.cs

using UnityEngine;

public class FilterFileExtensionAttribute : PropertyAttribute
{
    public string fileExtension = string.Empty;

    public FilterFileExtensionAttribute (string fileExtension)
    {
        this.fileExtension = fileExtension;
    }
}

FilterFileExtensionDrawer.cs

using UnityEditor;
using UnityEngine;
using System.IO;

[CustomPropertyDrawer (typeof (FilterFileExtensionAttribute))]
public class FilterFileExtensionDrawer : PropertyDrawer
{
    public override float GetPropertyHeight (SerializedProperty property, GUIContent label)
    {
        return EditorGUI.GetPropertyHeight(property, label, true);
    }

    public override void OnGUI (Rect position, SerializedProperty property, GUIContent label)
    {
        FilterFileExtensionAttribute attr = attribute as FilterFileExtensionAttribute;
        if (property.objectReferenceValue != null)
        {
            string path = AssetDatabase.GetAssetPath (property.objectReferenceValue);
            if (Path.GetExtension (path).Equals ("." + attr.fileExtension) == false)
            {
                Debug.LogErrorFormat ("{0} is not {1}", property.objectReferenceValue.name, attr.fileExtension);
                property.objectReferenceValue = null;
            }
        }
        EditorGUI.PropertyField (position, property, label);
    }
}