graphics - Difference between "screen size" and "screen density" in Android?

Question

I have a few questions:

1. What is the screen size?

2. What is the screen density?

3. What is a difference between screen size and screen density?

4. How I can support different densities and different screen sizes in Android?

I have already read the official documentation, but I was unable to understand the difference between screen size and screen density.

Answer 1

• Screen density means how many pixels appear within a constant area of the display, dots per inch = dpi
• Screen size means amount of physical space available for displaying an interface, screen's diagonal, inch
• Screen resolution means number of pixels available in the display, scale-independent pixel = sp
• density-independent pixel = virtual pixel that is independent of the screen density, dp

Density Classes:

Icon Sizes:

• (1) Google documentation says: "Applications should not generally worry about this density; relying on XHIGH graphics being scaled up to it should be sufficient for almost all cases."
• Launcher icons for Android Market: 512x512 px.

Screen Size Classes:

Screen Configuration:

• (1) To emulate this configuration, specify a custom density of 160 when creating an Android Virtual Device that uses a WVGA800 or WVGA854 skin.
• (2) To emulate this configuration, specify a custom density of 120 when creating an Android Virtual Device that uses a WVGA800 or WVGA854 skin.
• (3) This skin is available with the Android 3.0 platform.

Best Practices:

• Use wrap_content, match_parent, or dp units when specifying dimensions in an XML layout file. Except for defining text sizes: sp (scaling depends on user setting)

• Do not use hard coded pixel values in your application code.

• Do not use AbsoluteLayout,use Relative Layout.

• Supply alternative bitmap drawables for different screen densities.

• Provide a launcher icon for xxhdpi, but no other icons.