Android DPI computing and unit conversion

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. The diagonal line length of the mobile phone screen.	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.

 

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.htmlAs shown in figure 3, most mobile phone users with resolution 800*480 and 854*480

 Figure 3

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

The following describes the mutual conversion of several different units.

Public static int dip2px (context, float dipvalue ){
Final float scale = context. getresources (). getdisplaymetrics (). density;
Return (INT) (dipvalue * scale + 0.5f );
}
Public static int px2dip (context, float pxvalue ){
Final float scale = context. getresource (). getdisplaymetrics (). density;
Return (INT) (pxvalue/scale + 0.5f );
}
Public static int dip2px (context, float dipvalue ){
Final float scale = context. getresources (). getdisplaymetrics (). density;
Return (INT) (dipvalue * scale + 0.5f );
}
Public static int px2dip (context, float pxvalue ){
Final float scale = context. getresource (). getdisplaymetrics (). density;
Return (INT) (pxvalue/scale + 0.5f );
}

The following describes how to obtain the Resolution:

Write the following code in the oncreate method of an activity:
Displaymetrics metric = new displaymetrics ();
Getwindowmanager (). getdefaultdisplay (). getmetrics (metric );
Int width = metric. widthpixels; // screen width (pixels)
Int Height = metric. heightpixels; // screen height (pixels)
Float density = metric. density; // screen density (0.75/1.0/1.5)
Int densitydpi = metric. densitydpi; // screen density DPI (120/160/240)
This is quite simple, but have you tried it on a 800*480 machine? Is it 533 in width? Because the default density of Android is 1.0 at the beginning, you can add it to manifest. xml.

1. Uses-SDK node, <uses-SDK Android: minsdkversion = "4"/>, indicates that your APK cannot be installed on machines earlier than sdk1.6.

2. Supports-screens node.

<Supports-screens
Android: smallscreens = "true"
Android: normalscreens = "true"
Android: largescreens = "true"
Android: resizeable = "true"
Android: anydensity = "true"/>

Table 2