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;
        }
    }
}