Article 3. Pre-development knowledge supplement: length units and screen resolutions of Android, which are also reproduced ~~, Android screen resolution

Article 3. Pre-development knowledge supplement: length units and screen resolutions of Android, which are also reproduced ~~, Android screen resolution
This article is a bit early, but it is very practical. For more information about the Unit, see the red part.

Screen Resolution Basics

1. terms and concepts

Terms	Description	Remarks
Screen size)	It refers to the actual physical size of the mobile phone, such as the commonly used 2.8 inch, 3.2 inch, 3.5 inch, 3.7 inch	Motorola's milestone mobile phone is 3.7 inch
Aspect Ratio (width/height Ratio)	Refers to the actual physical size width/height ratio, divided into long and nolong	Milestone is and belongs to long
Resolution (Resolution)	Similar to the definition of computer resolution, it refers to the number of pixels in the portrait and horizontal directions of the mobile phone screen.	Milestone is 854*480
DPI (dot per inch)	Number of pixels per inch, such as 120 dpi and 320 dpi. Assume that the physical size of the QVGA (240*2 inch) resolution screen is (1.5 inch * 160), dpi =	Can reflect the definition of the screen, used to scale the UI
Density (Density)	The pixel value concentration in the Screen. resolution/Screen size can reflect the cell phone density,
Density-independent pixel (dip)	The Unit for calculating the logic density. The formula for the dip and the specific pixel value is dip/pixel = dpi/160, that is, px = dp * (dpi/160)

 

2. DPI Value Calculation

For example, calculate the WVGA (800*480) Resolution, 3.7 inch density DPI, as shown in 1

 

Figure 1

Diagonal pixel indicates the pixel value of the Diagonal line (=), DPI = 933/3. 7 = 252

 

3. Mobile phone screen Classification

 

3.1 is divided into the following three categories based on the cell phone screen density (DPI) or screen size, as shown in figure 2.

 

Figure 2

3. 2 The relationship between mobile phone screen classification and pixel density is shown in Table 1:

	Lowdensity (120), ldpi	Medium density (1, 160), mdpi	High density (240), hdpi
Small screen	QVGA (240x320)
Normal screen	WQVGA400 (240x400) WQVGA432 (240x432)	HVGA (320x480)	WVGA800 (480x800) WVGA854 (480x854)
Large screen		WVGA800 * (480x800) WVGA854 * (480x854)

Table 1

3.3 mobile phone size distribution (http://developer.android.com/resources/dashboard/screens.html) 3 shows, the current is mainly to the resolution of 800*480 and 854*480 mobile phone users mostly

 

 

Figure 3

From the above screen size distribution, we can only consider mobile phones with a density of 1 and 1.5 between 3-inches.

4. uidesign

From the perspective of development, the application provides three sets of UI layout files based on the screen of three types of Android phones, but three sets of corresponding interface icons are also required, as shown in table 2.

Icon Type	Standard Asset Sizes (in Pixels), for Generalized Screen Densities
	Low density screen (ldpi)	Medium density screen (mdpi)	High density screen (hdpi)
Launcher	36x36 px	48x48 px	72x72 px
Menu	36x36 px	48x48 px	72x72 px
Status Bar	24x24 px	32x32 px	48x48 px
Tab	24x24 px	32x32 px	48x48 px
Dialog	24x24 px	32x32 px	48x48 px
List View	24x24 px	32x32 px	48x48 px

Table 2

5. How can I achieve adaptive screen size?

1) interface Layout

Five layout, similar to the title bar of the windos window), layout-small (layout with a screen size less than 3 inch), layout-normal (screen size less than 4.5 inch ), layout-large (between 4 inch and 7 inch), layout-xlarge (between 7 and 10 inch)

2) image resources

You need to prepare 5 sets of image resources, including drawable, drawalbe-ldpi, drawable-mdpi, drawable-hdpi, and drawable-xhdpi Based on the dpi value.

Android has an automatic matching mechanism to select the corresponding layout and image resources.

 

Http://blog.csdn.net/moruite/article/details/6028547

Length unit basics 1. Overview

In the past, programmers often designed computer user interfaces 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. The screen density is different from the resolution.

Android has the following screens:

Screen Tyep	Width Pixels	Height Pixels	Dimensions 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, TextView'sIt is best to use sp as the unit for font size.And the source code of TextView shows that Android uses sp as the font size unit by default. Units that use dip as other elements.