Differences between DIP, DP, SP, PT, and PX in Android

1. Overview

Past,ProgramUsers usually design the computer user interface in pixels. For example, the image size is 80x32 pixels. The problem with this processing is that if you run the program on a new display with a dot (DPI) higher per inch, the user interface will look small. In some cases, the user interface may be small to difficult to see the content. Therefore, we can solve this problem by developing a program using a measurement unit unrelated to the resolution. Android Application Development supports different measurement units.

2. Meaning of measurement units

Dip: Device Independent pixels (device independent pixel ). different devices have different display effects, which are related to the hardware of the device. We recommend that you use this function to support WVGA, hvga, and qvga without pixels.

DP: dip is the same

Px: pixels (pixels). Different devices have the same display effect. Generally, we use hvga to represent 320x480 pixels, which is usually used.

PT: point, a standard unit of length, 1pt = 1/72 inch, used in the printing industry, very easy to use;
SP: scaled pixels (zoom in pixels). It is mainly used to display the best for textsize in fonts.

In (INCHES): the unit of length.
Mm (mm): the unit of length.

3. Conversion Formula of measurement units

In the android source code package typedvalue. Java, we can look at the following functions:

Public static float applydimension (INT unit, float value,

Displaymetrics metrics)

{

Switch (unit ){

Case complex_unit_px:

Return value;

Case complex_unit_dip:

Return Value * metrics. density;

Case complex_unit_sp:

Return Value * metrics. scaleddensity;

Case complex_unit_pt:

Return Value * metrics. xdpi * (1.0f/72 );

Case complex_unit_in:

Return Value * metrics. xdpi;

Case complex_unit_mm:

Return Value * metrics. xdpi * (1.0f/25.4f );

}

Return 0;

}

This function converts units to pixels.

Metrics. Density: The default value is density_device/(float) density_default;

Metrics. scaleddensity: The default value is density_device/(float) density_default;

Metrics. xdpi: The default value is density_device;

Density_device: screen Density

Density_default: The default value is 160.

 

4. Screen density:The number of display points per inch is different from the resolution.

Android has the following screens:

screen tyep	width pixels	height pixels	size range (INCHES)	screen density
Qvga	240	320	2.6-3.0	Low
Wqvga	240	400	3.2-3.5	Low
Fwqvga	240	432	3.5-3.8	Low
Hvga	320	480	3.0-3.5	Medium
WVGA	480	800	3.3-4.0	High
Fwvga	480	854	3.5-4.0	High
WVGA	480	800	4.8-5.5	Medium
Fwvga	480	854	5.0-5.8	Medium
Remarks	Currently, the default Android low = 120; medium = 160; high = 240

5. To sum up

 Based on PX = dip * density/160, when the screen density is 160, PX = dip
According to Google's suggestion, it is best to use SP as the unit for the font size of textview, and check the source code of textview. Android uses SP as the font size unit by default. Units that use dip as other elements.
URL:Http://greatverve.cnblogs.com/archive/2011/12/27/Android-dip-dp-sp-pt-px.html