[iOS base Control-4.6] length units in iOS development

For the location that is set in development, the unit system of dimensions is converted to pixel units according to the nature of the screen because the retina screen is twice times the resolution of the retina screen in the same size, so

• Non-Retina screen: 1 units = 1 pixels
• Retina Screen: 1 units = 2 pixels

For non-retina and retina screens, apps sometimes offer two images of different sizes, 1 time times and twice times, and their pixels are one-fold apart. Naming rules: twice times the graph after 1 time times the name plus @2x

• Normal: Sample.png
• Twice times: [Email protected]

When the system uses "sample" to find pictures, it automatically takes the corresponding pictures according to the screen of the device.

[iOS base Control-4.6] length units in iOS development