Unity editor window that used to pick an object from the asset database such as scriptable objects or prefabs which contains specific component.

ObjectPickerEditorWindow.cs

using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

namespace LuviKunG.Editor
{
    using UnityObject = UnityEngine.Object;

    /// <summary>
    /// An editor window that allows the user to pick an object of a specific type.
    /// </summary>
    public sealed class ObjectPickerEditorWindow : EditorWindow
    {
        private const string WINDOW_TITLE = "Pick an object...";

        private const string HELPBOX_MESSAGE_ERROR_NO_TYPE = "There are no type to pick.";
        private const string HELPBOX_MESSAGE_NO_ASSETS_FOUND = "There are no assets found to pick.";

        private static readonly GUIContent s_windowTitle;

        private Type type;
        private Action<UnityObject> onPick;
        private List<UnityObject> assets;

        private Vector2 scrollPosition;

        static ObjectPickerEditorWindow()
        {
            s_windowTitle = new GUIContent(WINDOW_TITLE);
        }

        /// <summary>
        /// Show the object picker window.
        /// </summary>
        /// <typeparam name="T">Type of the object to pick.</typeparam>
        /// <param name="onPick">Callback when an object is picked.</param>
        /// <returns>The object picker window.</returns>
        public static ObjectPickerEditorWindow DisplayPicker<T>(Action<T> onPick) where T : UnityObject
        {
            ObjectPickerEditorWindow window = CreateInstance<ObjectPickerEditorWindow>();
            window.titleContent = s_windowTitle;
            window.type = typeof(T);
            window.onPick = (obj) => onPick?.Invoke(obj as T);
            window.Fetch();
            window.ShowAuxWindow();
            return window;
        }

        private void OnGUI()
        {
            using (var scrollViewScope = new EditorGUILayout.ScrollViewScope(scrollPosition))
            {
                scrollPosition = scrollViewScope.scrollPosition;
                if (type == null)
                {
                    EditorGUILayout.HelpBox(HELPBOX_MESSAGE_ERROR_NO_TYPE, MessageType.Error, true);
                }
                else if (assets == null || assets.Count == 0)
                {
                    EditorGUILayout.HelpBox(HELPBOX_MESSAGE_NO_ASSETS_FOUND, MessageType.Info, true);
                }
                else
                {
                    using (new EditorGUILayout.VerticalScope())
                    {
                        for (int i = 0; i < assets.Count; i++)
                        {
                            UnityObject asset = assets[i];
                            if (GUILayout.Button(asset.name, EditorStyles.objectField, GUILayout.ExpandWidth(true)))
                            {
                                onPick?.Invoke(asset);
                                Close();
                            }
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Fetch assets of the specified type to this window.
        /// </summary>
        private void Fetch()
        {
            assets = new List<UnityObject>();
            if (type.IsSubclassOf(typeof(Component)))
            {
                string[] assetGuids = AssetDatabase.FindAssets("t:prefab", null);
                for (int i = 0; i < assetGuids.Length; i++)
                {
                    string path = AssetDatabase.GUIDToAssetPath(assetGuids[i]);
                    GameObject gameObject = AssetDatabase.LoadAssetAtPath<GameObject>(path);
                    if (gameObject != null)
                    {
                        Component component = gameObject.GetComponent(type);
                        if (component != null)
                        {
                            assets.Add(component);
                        }
                    }
                }
            }
            else if (type.IsSubclassOf(typeof(ScriptableObject)))
            {
                string[] assetGuids = AssetDatabase.FindAssets("t:" + type.Name, null);
                for (int i = 0; i < assetGuids.Length; i++)
                {
                    string path = AssetDatabase.GUIDToAssetPath(assetGuids[i]);
                    UnityObject asset = AssetDatabase.LoadAssetAtPath(path, type);
                    if (asset != null)
                    {
                        assets.Add(asset);
                    }
                }
            }
            else if (type.IsSubclassOf(typeof(UnityObject)))
            {
                string[] assetGuids = AssetDatabase.FindAssets("t:" + type.Name, null);
                for (int i = 0; i < assetGuids.Length; i++)
                {
                    string path = AssetDatabase.GUIDToAssetPath(assetGuids[i]);
                    UnityObject asset = AssetDatabase.LoadAssetAtPath(path, type);
                    if (asset != null)
                    {
                        assets.Add(asset);
                    }
                }
            }
        }
    }
}