通過程式去了解硬體情況是一件十分有意思的事情。很早我就研究在WM6.5上獲得螢幕物理尺寸，但一直沒有成功。後來又想要在Android上有所突破，不過在今天之前得到的尺寸都不準確。雖然很多人認為沒必要這麼較真，因為貌似很多情況下用不到。不過我就當這是一件很有挑戰性的事，一定要做到。對，就是這麼任性。

原始碼中android.view包下的Display類提供了很多方法供程式設計師獲得顯示相關的資訊，通過此類讓我們開啟瞭解裝置螢幕之旅吧。

一、解析度

此方法原型如下：

public void getSize(Point outSize) {  
    synchronized (this) {  
        updateDisplayInfoLocked();  
        mDisplayInfo.getAppMetrics(mTempMetrics, mDisplayAdjustments);  
        outSize.x = mTempMetrics.widthPixels;  
        outSize.y = mTempMetrics.heightPixels;  
    }  
}  
 

private void getDisplayInfomation() {  
    Point point = new Point();  
    getWindowManager().getDefaultDisplay().getSize(point);  
    Log.d(TAG,"the screen size is "+point.toString());  
}  

D/MainActivity﹕ the screen size is Point(800, 1280)
 

public void getRealSize(Point outSize) {  
    synchronized (this) {  
        updateDisplayInfoLocked();  
        outSize.x = mDisplayInfo.logicalWidth;  
        outSize.y = mDisplayInfo.logicalHeight;  
    }  
}  

android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen"  
android:theme="@android:style/Theme.NoTitleBar.Fullscreen"  

private void getDisplayInfomation() {  
    Point point = new Point();  
    getWindowManager().getDefaultDisplay().getSize(point);  
    Log.d(TAG,"the screen size is "+point.toString());  
    getWindowManager().getDefaultDisplay().getRealSize(point);  
    Log.d(TAG,"the screen real size is "+point.toString());  
}  

D/MainActivity﹕ the screen size is Point(800, 1202)  
D/MainActivity﹕ the screen real size is Point(800, 1280) 

二、螢幕尺寸

下面先介紹一下密度的概念，DPI、PPI，最後講解一下如何根據獲得的Display資訊去求出螢幕尺寸。這是一個困擾我很久的問題了。

方法一:

WindowManager wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);
int width = wm.getDefaultDisplay().getWidth();
int height = wm.getDefaultDisplay().getHeight();

WindowManager wm1 = this.getWindowManager();
int width1 = wm1.getDefaultDisplay().getWidth();
int height1 = wm1.getDefaultDisplay().getHeight();

WindowManager manager = this.getWindowManager();
DisplayMetrics outMetrics = new DisplayMetrics();
manager.getDefaultDisplay().getMetrics(outMetrics);
int width = outMetrics.widthPixels;
int height = outMetrics.heightPixels;

Resources resources = this.getResources();
DisplayMetrics dm = resources.getDisplayMetrics();
float density = dm.density;
int width = dm.widthPixels;
int height = dm.heightPixels;

三、螢幕密度

DENSITY_LOW = 120  
DENSITY_MEDIUM = 160  //預設值  
DENSITY_TV = 213      //TV專用  
DENSITY_HIGH = 240  
DENSITY_XHIGH = 320  
DENSITY_400 = 400  
DENSITY_XXHIGH = 480  
DENSITY_XXXHIGH = 640  

private void getDensity() {  
    DisplayMetrics displayMetrics = getResources().getDisplayMetrics();  
    Log.d(TAG,"Density is "+displayMetrics.density+" densityDpi is "+displayMetrics.densityDpi+" height: "+displayMetrics.heightPixels+  
        " width: "+displayMetrics.widthPixels);  
}  

1. the screen size is Point(1600, 2438)  
2. the screen real size is Point(1600, 2560)  
3. Density is 2.0 densityDpi is 320 height: 2438 width: 1600 

private void getScreenSizeOfDevice() {  
    DisplayMetrics dm = getResources().getDisplayMetrics();  
    int width=dm.widthPixels;  
    int height=dm.heightPixels;  
    double x = Math.pow(width,2);  
    double y = Math.pow(height,2);  
    double diagonal = Math.sqrt(x+y);  
  
    int dens=dm.densityDpi;  
    double screenInches = diagonal/(double)dens;  
    Log.d(TAG,"The screenInches "+screenInches);  
} 

01-13 16:35:03.026  16601-16601/com.linc.listviewanimation D/MainActivity﹕ the screen size is Point(1600, 2438)  
01-13 16:35:03.026  16601-16601/com.linc.listviewanimation D/MainActivity﹕ the screen real size is Point(1600, 2560)  
01-13 16:35:03.026  16601-16601/com.linc.listviewanimation D/MainActivity﹕ Density is 2.0 densityDpi is 320 height: 2438 width: 1600 xdpi 338.666 ydpi 338.666  
01-13 16:35:03.026  16601-16601/com.linc.listviewanimation D/MainActivity﹕ The screenInches 9.112922229586951  

四、PPI

//The exact physical pixels per inch of the screen in the X/Y dimension. 

private void getScreenSizeOfDevice2() {  
    Point point = new Point();  
    getWindowManager().getDefaultDisplay().getRealSize(point);  
    DisplayMetrics dm = getResources().getDisplayMetrics();  
    double x = Math.pow(point.x/ dm.xdpi, 2);  
    double y = Math.pow(point.y / dm.ydpi, 2);  
    double screenInches = Math.sqrt(x + y);  
    Log.d(TAG, "Screen inches : " + screenInches);  
}  

01-13 16:58:50.142  17249-17249/com.linc.listviewanimation D/MainActivity﹕ Screen inches : 8.914015757534717  

五、DIP

//pixel = dip*density;  
private int convertDpToPixel(int dp) {  
    DisplayMetrics displayMetrics = mContext.getResources().getDisplayMetrics();  
    return (int)(dp*displayMetrics.density);  
}  
  
private int convertPixelToDp(int pixel) {  
    DisplayMetrics displayMetrics = mContext.getResources().getDisplayMetrics();  
    return (int)(pixel/displayMetrics.density);  
}