ShowFileExtensions.cs

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

[InitializeOnLoad]
public static class ShowFileExtensions
{
	// ================================================================================
	//  static constructor
	// --------------------------------------------------------------------------------

	static ShowFileExtensions()
	{
		EditorApplication.projectWindowItemOnGUI += ProjectWindowItemOnGUI;
	}

	// ================================================================================
	//  checking editor events
	// --------------------------------------------------------------------------------

	private static void ProjectWindowItemOnGUI(string guid, Rect rect)
	{
		if (Event.current.alt)
		{
			EditorWindow window = GetProjectWindow();			

			string assetPath = AssetDatabase.GUIDToAssetPath(guid);
			UnityEngine.Object obj = AssetDatabase.LoadAssetAtPath<UnityEngine.Object>(assetPath);

			if (obj != null && AssetDatabase.IsMainAsset(obj) && !IsDirectory(obj))
			{
				if (showsBigIcons)
				{
					// just draw it bold in upper left
					string extension = Path.GetExtension(assetPath);
					GUI.Label(rect, extension, EditorStyles.boldLabel);
				}
				else
				{
					// we overpaint the filename here, does look a bit dirty and might need adjustment of the offset
					var labelRect = rect.Translate(new Vector2(19f, 1f));
					var fileName = Path.GetFileName(assetPath);
					GUI.Label(labelRect, fileName);
				}
			}

			EditorApplication.RepaintProjectWindow();
		}
	}

	// ================================================================================
	//  getting infos about the project window
	// --------------------------------------------------------------------------------

	private static bool showsBigIcons
	{
		get
		{
			return isTwoColumnMode && listAreaGridSize > 16f;
		}
	}

	private static bool isTwoColumnMode
	{
		get
		{
			var projectWindow = GetProjectWindow();

			var projectWindowType = projectWindow.GetType();
			var modeFieldInfo = projectWindowType.GetField("m_ViewMode", BindingFlags.Instance | BindingFlags.NonPublic);

			int mode = (int)modeFieldInfo.GetValue(projectWindow);

			// 0 == ViewMode.OneColumn
			// 1 == ViewMode.TwoColum

			return mode == 1;
		}
	}

	private static float listAreaGridSize
	{
		get
		{
			var projectWindow = GetProjectWindow();

			var projectWindowType = projectWindow.GetType();
			var propertyInfo = projectWindowType.GetProperty("listAreaGridSize", BindingFlags.Instance | BindingFlags.Public);
			return (float)propertyInfo.GetValue(projectWindow, null);
		}
	}

	/// <summary>
	/// there's a chance here we get the wrong one when two project windows are open
	/// </summary>
	private static EditorWindow GetProjectWindow()
	{
		if (EditorWindow.focusedWindow != null && EditorWindow.focusedWindow.titleContent.text == "Project")
		{
			return EditorWindow.focusedWindow;
		}

		return GetExistingWindowByName("Project");
	}

	private static EditorWindow GetExistingWindowByName(string name)
	{
		EditorWindow[] windows = Resources.FindObjectsOfTypeAll<EditorWindow>();
		foreach (var item in windows)
		{
			if (item.titleContent.text == name)
			{
				return item;
			}
		}

		return default(EditorWindow);
	}

	// ================================================================================
	//  utilities
	// --------------------------------------------------------------------------------

	private static Rect Translate(this Rect rect, Vector2 delta)
	{
		rect.x += delta.x;
		rect.y += delta.y;

		return rect;
	}

	private static bool IsDirectory(UnityEngine.Object obj)
	{
		if (obj == null)
		{
			return false;
		}

		return obj is DefaultAsset && !AssetDatabase.IsForeignAsset(obj);
	}
}