ImageView
android:adjustViewBounds
Set this to true if you want the ImageView to adjust its bounds to preserve the aspect ratio of its drawable.
Note: If the application targets API level 17 or
lower, adjustViewBounds will allow the drawable to shrink the view bounds, but
not grow to fill available measured space in all cases. This is for
compatibility with legacy MeasureSpec and RelativeLayout behavior.
是否保持宽高比。需要与maxWidth、MaxHeight一起使用，否则单独使用没有效果。
android:cropToPadding
是否截取指定区域用空白代替。单独设置无效果，需要与scrollY一起使用