Android屏幕密度dpi与PPI

根据android文档,密度应以dpi(每英寸的点数)为单位,所有布局尺寸应以dp为单位.

并使用一个简单的公式android可以将dp映射到实际像素.

px = dp * (dpi / 160), 
160dpi ~ medium density screen which is the baseline

那么,为什么不只使用ppi(每英寸像素)来描述屏幕密度呢？

解决方法:

关于此问题有很多文档,但是我认为这部分与您的问题有关：

Supporting Multiple Screens

Density independence

Your application achieves “density independence” when it preserves the
physical size (from the user’s point of view) of user interface
elements when displayed on screens with different densities.

Maintaining density independence is important because, without it, a
UI element (such as a button) appears physically larger on a
low-density screen and smaller on a high-density screen. Such
density-related size changes can cause problems in your application
layout and usability. figures 2 and 3 show the difference between an
application when it does not provide density independence and when it
does, respectively.