Android 单位
网址：https://developer.android.google.cn/guide/topics/resources/more-resources#Dimension
dp 密度无关单位 1dp = 1/160 inch 和物理尺寸做对应
Density-independent Pixels - An abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi (dots per inch) screen, on which 1dp is roughly equal to 1px.
sp 缩放无关像素 受屏幕密度与用户偏好影响
Scale-independent Pixels - This is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and the user's preference.
pt 1英寸72pt 和物理单位成关系的
Points - 1/72 of an inch based on the physical size of the screen, assuming a 72dpi density screen.
px 像素点 物理单位
Pixels - Corresponds to actual pixels on the screen.
mm 毫米 物理单位
Millimeters - Based on the physical size of the screen.
in 英寸 物理单位
Inches - Based on the physical size of the screen.