Of Stack

android gets the screen length and width of the implementation code of handwritten

  • 2020-05-07 20:24:17
  • OfStack

In android, the length of the screen is longer than the width, referring to a lot of code on the Internet, but the result is not consistent with the actual, such as my phone is i9000, screen size is 480*800px, the result is 320*533
The result is very unreliable, so I wrote a few lines of code, test 1
Test parameters:
Test environment: i9000(3 stars)
Physical screen: 480*800px
density: 1.5

test code : 

 
//  Gets screen density (method) 1 )  
int screenWidth = getWindowManager().getDefaultDisplay().getWidth(); //  Screen width (pixels, e.g. : 480px )  
int screenHeight = getWindowManager().getDefaultDisplay().getHeight(); //  Screen height (pixels, e.g. : 800p )  
Log.e(TAG + " getDefaultDisplay", "screenWidth=" + screenWidth + "; screenHeight=" + screenHeight); 
//  Gets screen density (method) 2 )  
DisplayMetrics dm = new DisplayMetrics(); 
dm = getResources().getDisplayMetrics(); 
float density = dm.density; //  Screen density (pixel ratio: 0.75/1.0/1.5/2.0 )  
int densityDPI = dm.densityDpi; //  Screen density (pixels per inch: 120/160/240/320 )  
float xdpi = dm.xdpi; 
float ydpi = dm.ydpi; 
Log.e(TAG + " DisplayMetrics", "xdpi=" + xdpi + "; ydpi=" + ydpi); 
Log.e(TAG + " DisplayMetrics", "density=" + density + "; densityDPI=" + densityDPI); 
screenWidth = dm.widthPixels; //  Screen width (pixels, e.g. : 480px )  
screenHeight = dm.heightPixels; //  Screen height (pixels, e.g. : 800px )  
Log.e(TAG + " DisplayMetrics(111)", "screenWidth=" + screenWidth + "; screenHeight=" + screenHeight); 
//  Gets screen density (method) 3 )  
dm = new DisplayMetrics(); 
getWindowManager().getDefaultDisplay().getMetrics(dm); 
density = dm.density; //  Screen density (pixel ratio: 0.75/1.0/1.5/2.0 )  
densityDPI = dm.densityDpi; //  Screen density (pixels per inch: 120/160/240/320 )  
xdpi = dm.xdpi; 
ydpi = dm.ydpi; 
Log.e(TAG + " DisplayMetrics", "xdpi=" + xdpi + "; ydpi=" + ydpi); 
Log.e(TAG + " DisplayMetrics", "density=" + density + "; densityDPI=" + densityDPI); 
int screenWidthDip = dm.widthPixels; //  Screen width ( dip , such as: 320dip )  
int screenHeightDip = dm.heightPixels; //  Screen width ( dip , such as: 533dip )  
Log.e(TAG + " DisplayMetrics(222)", "screenWidthDip=" + screenWidthDip + "; screenHeightDip=" + screenHeightDip); 
screenWidth = (int)(dm.widthPixels * density + 0.5f); //  Screen width ( px , such as: 480px )  
screenHeight = (int)(dm.heightPixels * density + 0.5f); //  The screen height ( px , such as: 800px )  
Log.e(TAG + " DisplayMetrics(222)", "screenWidth=" + screenWidth + "; screenHeight=" + screenHeight);

results are as follows: 
 
E/== MyScreenActivity =================================== getDefaultDisplay( 8509): screenWidth=320; screenHeight=533 
E/== MyScreenActivity =================================== DisplayMetrics( 8509): xdpi=156.3077; ydpi=157.51938 
E/== MyScreenActivity =================================== DisplayMetrics( 8509): density=1.0; densityDPI=160 
E/== MyScreenActivity =================================== DisplayMetrics(111)( 8509): screenWidth=320; screenHeight=533 
E/== MyScreenActivity =================================== DisplayMetrics( 8509): xdpi=234.46153; ydpi=236.27907 
E/== MyScreenActivity =================================== DisplayMetrics( 8509): density=1.5; densityDPI=240 
E/== MyScreenActivity =================================== DisplayMetrics(222)( 8509): screenWidthDip=320; screenHeightDip=533 
E/== MyScreenActivity =================================== DisplayMetrics(222)( 8509): screenWidth=480; screenHeight=800


analysis results :
In the onDraw() method
The results of methods 1 and 2 are 1, both of which are 320*533, obviously not the screen size of the test machine i9000
Method 3, multiply the results of methods 1 and 2 by density, perfect 480*800, perfect!

note : if density is greater than 1, targetSdkVersion needs to be set between 4-9, for example
< uses-sdk android:minSdkVersion="3" android:targetSdkVersion="10" / >

But does this mean that method 31 must be universal?
The answer is no, because I have also tested it on emulators, HTC G14 physical machines, and ViewSonic and Galaxy tablets. Method 3 enlarges the actual screen value at density=1.5, for example: HTC G14
On HTC G14, the actual screen size is obtained directly from dm.widthPixels, dm.heightPixels (540,960)
The reason why it is impossible to obtain the real physical screen size through a common method may be that the Android system is open source, and different mobile phone manufacturers do not have a unified manufacturing standard to specify the mobile phone screen.

After careful analysis of the code, found the problem in code :
getWindowManager().getDefaultDisplay().getMetrics(dm)
Initialize a DisplayMetrics object from this display's data.
dm = getResources().getDisplayMetrics()
Return the current display metrics that are in effect for this resource object. The returned object should be treated as read-only.

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