Unity3D UGUI Image与父级保持比例缩放

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;

 public class X_RectAutoSize : MonoBehaviour
 {
     //原始尺寸
     private Vector2 olSize;
     //缩放后的尺寸
     private Vector2 size;
     //原始尺寸宽高比
     private float al;
     private RectTransform self;
     public bool lockHeight;
     public bool lockPos= true;
     internal float parentHeight;
     public float heightBoder;

     void Update()
     {
         self = GetComponent<RectTransform>();
         if (!lockHeight)
         {
             parentHeight = self.parent.GetComponent<RectTransform>().rect.size.y - heightBoder;
         }
         self.GetComponent<Image>().SetNativeSize();
         olSize = self.sizeDelta;
         al = olSize.x / olSize.y;
         size = new Vector2(parentHeight * al, parentHeight);
         self.sizeDelta = size;
         if (lockPos)
         {
             self.anchoredPosition = Vector2.zero;
         }
     }
 }