1、拉伸铺满

 RectTransform rect = GetComponent<RectTransform>();
        rect.anchorMin = Vector2.zero;
        rect.anchorMax = Vector2.one;
        rect.SetSizeWithCurrentAnchors(RectTransform.Axis.Horizontal, Screen.width);
        rect.SetSizeWithCurrentAnchors(RectTransform.Axis.Vertical, Screen.height);

2、向左居中对齐

        RectTransform rect = GetComponent<RectTransform>(); 
        rect .anchorMin = new Vector2(0, 0.5f);
        rect .anchorMax = new Vector2(0, 0.5f);
        rect .pivot = new Vector2(0, 0.5f);

3、修改大小并保持位置不变

        RectTransform rect = GetComponent<RectTransform>(); 
        rect .anchorMin = new Vector2(0, 0.5f);
        rect .anchorMax = new Vector2(0, 0.5f);
        rect .pivot = new Vector2(0, 0.5f);

        Vector3 originalPos = rect .localPosition;
        rect .sizeDelta += new Vector2(40, 0);
        rect .localPosition = originalPos new Vector3(40f / 2, 0);