OnPreviewGUI

gistfile1.cs

using UnityEngine;
using UnityEditor;

[CustomEditor(typeof(HogeScript))]
public class CompactWindow : Editor
{
  private Editor model;
	public override void OnInspectorGUI ()
	{
		HogeScript h = (HogeScript)target;
		h.model = (GameObject)EditorGUILayout.ObjectField (h.model, typeof(GameObject), false);
		
		if (h.model != null && model == null){
			model = Editor.CreateEditor (h.model);
		} else {
			model.OnPreviewGUI (GUILayoutUtility.GetRect (Screen.width, 256), EditorStyles.whiteLabel);
		}
	}
}