Size Issues in Android design

Android divides the screen size into four types: small, normal, large, xlarge;
The screen density is divided into: low (LDPI), Medium (MDPI), High (hdpi), Extra High (xhdpi), and the relationship between each screen density is as follows:

Density name	reference value for density (DPI)	Relationship	the corresponding screen resolution
xxxhdpi	640dpi
xxhdpi	480dpi
xhdpi	320dpi	2.0
hdpi	240dpi	1.5	800*480
mdpi	160dpi	1.0 (Benchmark)	480*320
ldpi	120dpi	0.75	320*240

DPI (dot per inch): The number of pixels per inch, 1 inches = 2.54 centimeters, usually said 4.3 inches, 4.5 inches is actually the length of the screen diagonal.

DP (density independent pixel): independent density pixels, using DP as the unit to set the control, regardless of the screen or the size of the DPI, its display is consistent, if you use PX, you will see inconsistent results. For example, a 160px-length segment with a density of 160dpi and a width of 1 inches fills the entire screen, while on a screen with a density of 320dpi and a width of 1 inches, only half of the screen is filled, that is, for two screens with the same physical size but different dpi, The difference in the display effect can be very large.

The relationship between pixel, DP, and DPI is as follows:

PX = DP * (dpi/160)

principle 1: When transduction the Android interface, 160DPI is generally used as a benchmark . Because the 160DIP as a benchmark, as long as the transduction of the length and width of the number of pixels is a multiple of 4, then xhdpi the figure on the length of the width of the number of pixels can be multiplied by 2,hdpi under the 1.5,ldpi multiplied by 0.75, the result of the resulting length and width of the number of pixels is an integer. If 240dpi is used as the benchmark, then the number of pixels in the 240-cut graph is a multiple of 3, and the corresponding number of pixels is multiplied by 1.333333,mdpi under xhdpi and multiplied by 0.66666,ldpi, which gives a non-shaping pixel count.

QVGA, the screen density of WQVGA is: 120
The screen density of the HVGA is: 160
The screen density of the WVGA is: 240
Where ldpi resources are not required, when providing hdpi resources, the system automatically shrinks the HDPI resources by half to fit the ldpi screen

Note: Screen density and screen resolution are different concepts, with screen resolution and size, you can calculate the screen density , for example, the resolution is 320*480, the screen size is 3.2 inches (diagonal length), the screen density is:

Note: Dip is DP

SP (scale independent pixel): scaling independent pixels, similar to DP, the only difference is that the unit is affected by the system font settings and is usually used in fonts. Common font sizes specified in the Android specification:

Displaymetrics class

Displaymetrics is a class that describes screen-related parameters and accesses the Displaymetrics method:

DisplayMetrics metrics = new DisplayMetrics();getWindowManager().getDefaultDisplay.getMetrics(metrics);

You can then access the individual constants, fields, and methods in the metrics variable.

• Density: Screen density
• DENSITYDPI: Screen density, in dpi
• Heightpixels: screen height, in pixels
• Widthpixels: Screen width, in pixels
• XDPI: Screen density in X-direction of the screen
• YDPI: Screen density in the Y-direction of the screen

Market data

Top-ranked screen resolutions:

resolution	percentage	screen Density
1280 * 720	29.2%	267 ~ 293 (hdpi, xhdpi)
800 * 480	18.5%	233 ~ 266 (HDPI)
854 * 480	13.8%	195 ~ 217 (MDPI, hdpi)
1920 * 1080	10.6%	367 ~ (xhdpi)
960 * 540	10%	~ 244 (HDPI)
480 * 320	4.1%
1184 * 720	3%

Data Source: Http://www.umindex.com/devices/android_resolutions

RELATED LINKS

1. Https://developer.android.com/design/style/devices-displays.html
2. Http://developer.android.com/training/basics/supporting-devices/screens.html
3. Http://www.25xt.com/allcode/4269.html

Size Issues in Android design