通过拖拽prefab来存储相应的路径

更新了一下，支持数组和嵌套数据结构。

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

 [CustomPropertyDrawer(typeof(ObjectToPathAttribute))]
 public class ObjectToPathDrawer : PropertyDrawer
 {

     public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
     {
         Object target = property.serializedObject.targetObject;
         ObjectToPathAttribute otpa = attribute as ObjectToPathAttribute;
         System.Type objType = otpa._objType;

         string path = property.stringValue;
         position.width = EditorGUIUtility.labelWidth * 2.0f / 3.0f;

         EditorGUI.LabelField(position, label);
         position.x += EditorGUIUtility.labelWidth * 2.0f / 3.0f;

         Object _obj = null;
         bool _foundObj = true;
         if (!string.IsNullOrEmpty(path))
         {
             _obj = AssetDatabase.LoadMainAssetAtPath(path);
             if (_obj == null)
             {
                 _foundObj = false;
             }
         }
         _obj = EditorGUI.ObjectField(position, _obj, objType, false);
         if (_obj != null)
         {
             path = AssetDatabase.GetAssetPath(_obj);
         }
         else
         {
             if (_foundObj)
             {
                 path = string.Empty;
             }
         }
         position.x += EditorGUIUtility.labelWidth * 2.0f / 3.0f;
         position.width = EditorGUIUtility.labelWidth;
         property.stringValue = EditorGUI.TextField(position, path);
     }
 }

ObjectToPathDrawer

 using UnityEngine;
 using System.Collections;

 public class ObjectToPathAttribute : PropertyAttribute
 {
     public System.Type _objType;
     public ObjectToPathAttribute(System.Type t)
     {
         _objType = t;
     }
 }

ObjectToPathAttribute

 using UnityEngine;
 using System.Collections;

 public class TestClass : MonoBehaviour
 {
     [ObjectToPath(typeof(GameObject))]
     public string _prefabPath;
 }

TestClass

使用上面的代码可以通过拖拽一个prefab的方式把相应的路径直接存储到public string _itemPerfabPath里，省去键盘输入步骤。不支持场景中的GameObject的拖入。

截图如下：

当prefab为空的时候的截图如下：