Basic Android mobile phone resolution knowledge (DPI, dip computing)

From: http://blog.csdn.net/moruite/article/details/6028547

1. terms and concepts

Terms	Description	Remarks
Screen Size)	It refers to the actual physical size of the mobile phone, such as commonly used 2.8 inch, 3.2 inch, 3.5 inch, 3.7 inch, diagonal	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 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.