Android开发笔记：安卓程序截屏方法

1,基于Android SDK的截屏方法

(1)主要就是利用SDK提供的View.getDrawingCache()方法。网上已经有很多的实例了。首先创建一个android project，然后进行Layout，画一个按键（res/layout/main.xml）：

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

>

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/hello"

/>

<Button

android:text="NiceButton"

android:id="@+id/my_button"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"></Button>

</LinearLayout>

HelloAndroid.java实现代码为：

packagecom.example.helloandroid;

importjava.io.FileOutputStream;

importjava.text.SimpleDateFormat;

importjava.util.Date;

importjava.util.Locale;

importandroid.app.Activity;

importandroid.graphics.Bitmap;

importandroid.os.Bundle;

importandroid.view.View;

importandroid.view.View.OnClickListener;

importandroid.widget.Button;

publicclassHelloAndroidextendsActivity {

privateButton button;

/** Called when the activity is first created. */

@Override

publicvoidonCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

this.setContentView(R.layout.main);

this.button = (Button) this.findViewById(R.id.my_button);

this.button.setOnClickListener(newOnClickListener() {

publicvoidonClick(View v) {

SimpleDateFormat sdf = newSimpleDateFormat(

"yyyy-MM-dd_HH-mm-ss", Locale.US);

String fname = "/sdcard/"+ sdf.format(newDate()) + ".png";

View view = v.getRootView();

view.setDrawingCacheEnabled(true);

view.buildDrawingCache();

Bitmap bitmap = view.getDrawingCache();

if(bitmap != null) {

System.out.println("bitmap got!");

try{

FileOutputStream out = newFileOutputStream(fname);

bitmap.compress(Bitmap.CompressFormat.PNG,100, out);

System.out.println("file " + fname + "output done.");

}catch(Exception e) {

e.printStackTrace();

}

}else{

System.out.println("bitmap is NULL!");

}

});

}

这个代码会在按下app中按键的时候自动在手机的/sdcard/目录下生成一个时间戳命名的png截屏文件。

这种截屏有一个问题，就是只能截到一部分，比如电池指示部分就截不出来了。

(2)在APK中调用“adb shell screencap -pfilepath” 命令

该命令读取系统的framebuffer，需要获得系统权限：

（1）. 在AndroidManifest.xml文件中添加

<uses-permissionandroid:name="android.permission.READ_FRAME_BUFFER"/>

（2）. 修改APK为系统权限，将APK放到源码中编译，修改Android.mk

LOCAL_CERTIFICATE := platform

```
publicvoid takeScreenShot(){ 
```

   String mSavedPath = Environment.getExternalStorageDirectory()+File. separator + "screenshot.png" ;

```
try {                     
```

          Runtime. getRuntime().exec("screencap -p " + mSavedPath);

```
   } catch (Exception e) { 
```
```
          e.printStackTrace();
```
```
   }
```

(3).利用系统的API，实现Screenshot,这部分代码是系统隐藏的，需要在源码下编译，

1).修改Android.mk，添加系统权限

LOCAL_CERTIFICATE := platform

2).修改AndroidManifest.xml 文件，添加

权限

<uses-permissionandroid:name="android.permission.READ_FRAME_BUFFER"/>

public boolean takeScreenShot(String imagePath){

if(imagePath.equals("" )){

imagePath = Environment.getExternalStorageDirectory()+File. separator+"Screenshot.png" ;

}

Bitmap mScreenBitmap;

WindowManager mWindowManager;

DisplayMetrics mDisplayMetrics;

Display mDisplay;

mWindowManager = (WindowManager) mcontext.getSystemService(Context.WINDOW_SERVICE);

mDisplay = mWindowManager.getDefaultDisplay();

mDisplayMetrics = new DisplayMetrics();

mDisplay.getRealMetrics(mDisplayMetrics);

float[] dims = {mDisplayMetrics.widthPixels , mDisplayMetrics.heightPixels };

mScreenBitmap = Surface. screenshot((int) dims[0], ( int) dims[1]);

if (mScreenBitmap == null) {

return false ;

}

try {

FileOutputStream out = new FileOutputStream(imagePath);

mScreenBitmap.compress(Bitmap.CompressFormat. PNG, 100, out);

} catch (Exception e) {

return false ;

}

return true ;

}

2 基于Android ddmlib进行截屏

public class ScreenShot {
private BufferedImage image = null;
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
AndroidDebugBridge.init(false); //
ScreenShot screenshot = new ScreenShot();
IDevice device = screenshot.getDevice();
for (int i = 0; i < 10; i++) {
Date date=new Date();
SimpleDateFormat df=new SimpleDateFormat("MM-dd-HH-mm-ss");
String nowTime = df.format(date);
screenshot.getScreenShot(device, "Robotium" + nowTime);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void getScreenShot(IDevice device,String filename) {
RawImage rawScreen = null;
try {
rawScreen = device.getScreenshot();
} catch (TimeoutException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (AdbCommandRejectedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if (rawScreen != null) {
Boolean landscape = false;
int width2 = landscape ? rawScreen.height : rawScreen.width;
int height2 = landscape ? rawScreen.width : rawScreen.height;
if (image == null) {
image = new BufferedImage(width2, height2,
BufferedImage.TYPE_INT_RGB);
} else {
if (image.getHeight() != height2 || image.getWidth() != width2) {
image = new BufferedImage(width2, height2,
BufferedImage.TYPE_INT_RGB);
}
}
int index = 0;
int indexInc = rawScreen.bpp >> 3;
for (int y = 0; y < rawScreen.height; y++) {
for (int x = 0; x < rawScreen.width; x++, index += indexInc) {
int value = rawScreen.getARGB(index);
if (landscape)
image.setRGB(y, rawScreen.width - x - 1, value);
else
image.setRGB(x, y, value);
}
}
try {
ImageIO.write((RenderedImage) image, "PNG", new File("D:/"
+ filename + ".jpg"));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
/**
* 获取得到device对象
* @return
*/
private IDevice getDevice(){
IDevice device;
AndroidDebugBridge bridge = AndroidDebugBridge
.createBridge("adb", true);//如果代码有问题请查看API，修改此处的参数值试一下
waitDevicesList(bridge);
IDevice devices[] = bridge.getDevices();
device = devices[0];
return device;
}
/**
* 等待查找device
* @param bridge
*/
private void waitDevicesList(AndroidDebugBridge bridge) {
int count = 0;
while (bridge.hasInitialDeviceList() == false) {
try {
Thread.sleep(500);
count++;
} catch (InterruptedException e) {
}
if (count > 240) {
System.err.print("等待获取设备超时");
break;
}
}
}

3 Android本地编程（Native Programming）读取framebuffer

(1)命令行，框架的截屏功能是通过framebuffer来实现的，所以我们先来介绍一下framebuffer。

framebuffer介绍
帧缓冲（framebuffer）是Linux为显示设备提供的一个接口，把显存抽象后的一种设备，他允许上层应用程序在图形模式下直接对显示缓冲区进行 读写操作。这种操作是抽象的，统一的。用户不必关心物理显存的位置、换页机制等等具体细节。这些都是由Framebuffer设备驱动来完成的。
Linux FrameBuffer 本质上只是提供了对图形设备的硬件抽象，在开发者看来，FrameBuffer 是一块显示缓存，往显示缓存中写入特定格式的数据就意味着向屏幕输出内容。所以说FrameBuffer就是一块白板。例如对于初始化为16 位色的FrameBuffer 来说， FrameBuffer中的两个字节代表屏幕上一个点，从上到下，从左至右，屏幕位置与内存地址是顺序的线性关系。
帧缓存有个地址，是在内存里。我们通过不停的向frame buffer中写入数据， 显示控制器就自动的从frame buffer中取数据并显示出来。全部的图形都共享内存中同一个帧缓存。

Android截屏实现思路
Android系统是基于Linux内核的，所以也存在framebuffer这个设备，我们要实现截屏的话只要能获取到framebuffer中的数据，然后把数据转换成图片就可以了，android中的framebuffer数据是存放在 /dev/graphics/fb0 文件中的，所以我们只需要来获取这个文件的数据就可以得到当前屏幕的内容。
现在我们的测试代码运行时候是通过RC(remote controller)方式来运行被测应用的，那就需要在PC机上来访问模拟器或者真机上的framebuffer数据，这个的话可以通过android的ADB命令来实现。

具体实现

/***********************************************************************
  *
  *   ScreenShot.java
  ***********************************************************************/
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.DataInput;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.imageio.ImageIO;
import org.openqa.selenium.OutputType;
import org.openqa.selenium.internal.Base64Encoder;
import com.google.common.io.Closeables;
import com.google.common.io.LittleEndianDataInputStream;

/**
 */
public class ScreenShot {

    /**
     * @param args
     * @throws InterruptedException 
     */
    public static void main(String[] args) throws InterruptedException {    
        try {
            //分辨率大小，后续可以通过代码来获取到当前的分辨率
            int xResolution = 320;
            int yResolution = 480;
            //执行adb命令，把framebuffer中内容保存到fb1文件中
             Runtime.getRuntime().exec("adb pull /dev/graphics/fb0 C:/fb1");
             //等待几秒保证framebuffer中的数据都被保存下来，如果没有保存完成进行读取操作会有IO异常
             Thread.sleep(15000);
             //读取文件中的数据
             InputStream in = (InputStream)new FileInputStream("C:/fb1");
             DataInput frameBuffer = new LittleEndianDataInputStream(in);
             
             BufferedImage screenImage = new BufferedImage(
                     xResolution, yResolution, BufferedImage.TYPE_INT_ARGB);
                 int[] oneLine = new int[xResolution];
                for (int y = 0; y < yResolution; y++) {
                    //从frameBuffer中计算出rgb值
                    convertToRgba32(frameBuffer, oneLine);
                    //把rgb值设置到image对象中
                    screenImage.setRGB(0, y, xResolution, 1, oneLine, 0, xResolution);
                }
                Closeables.closeQuietly(in);
                
                ByteArrayOutputStream rawPngStream = new ByteArrayOutputStream();
                try {
                      if (!ImageIO.write(screenImage, "png", rawPngStream)) {
                        throw new RuntimeException(
                            "This Java environment does not support converting to PNG.");
                      }
                    } catch (IOException exception) {
                      // This should never happen because rawPngStream is an in-memory stream.
                     System.out.println("IOException=" + exception);
                    }
                byte[] rawPngBytes = rawPngStream.toByteArray();
                String base64Png = new Base64Encoder().encode(rawPngBytes);
                
                File screenshot = OutputType.FILE.convertFromBase64Png(base64Png);
                System.out.println("screenshot==" + screenshot.toString());
                screenshot.renameTo(new File("C:\\screenshottemp.png"));
                
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println(e);
        }
    }
    
    
    public static void convertToRgba32(DataInput frameBuffer, int[] into) {
        try {
            for (int x = 0; x < into.length; x++) {
                try{
                int rgb = frameBuffer.readShort() & 0xffff;
                int red = rgb >> 11;
                red = (red << 3) | (red >> 2);
                int green = (rgb >> 5) & 63;
                green = (green << 2) | (green >> 4);
                int blue = rgb & 31;
                blue = (blue << 3) | (blue >> 2);
                into[x] = 0xff000000 | (red << 16) | (green << 8) | blue;
                }catch (EOFException e){
                    System.out.println("EOFException=" + e);
                }
              }
        } catch (IOException exception) {
            System.out.println("convertToRgba32Exception=" + exception);
      }
    }
    
}

（2）

首先是直接移植SystemUI的代码，实现截图效果，这部分的代码就不贴出来了，直接去下载代码吧，关键的代码没有几句，最最主要的是：Surface.screenshot()，请看代码吧。
[java]
<SPAN style="FONT-SIZE: 16px">package org.winplus.ss;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.Display;
import android.view.Surface;
import android.view.WindowManager;
import android.os.SystemProperties;
public class SimpleScreenshotActivity extends Activity {
private Display mDisplay;
private WindowManager mWindowManager;
private DisplayMetrics mDisplayMetrics;
private Bitmap mScreenBitmap;
private Matrix mDisplayMatrix;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new Thread(new Runnable() {
@Override
public void run() {
takeScreenshot();
}
}).start();
}
private float getDegreesForRotation(int value) {
switch (value) {
case Surface.ROTATION_90:
return 360f - 90f;
case Surface.ROTATION_180:
return 360f - 180f;
case Surface.ROTATION_270:
return 360f - 270f;
}
return 0f;
}
private void takeScreenshot() {
mWindowManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
mDisplay = mWindowManager.getDefaultDisplay();
mDisplayMetrics = new DisplayMetrics();
mDisplay.getRealMetrics(mDisplayMetrics);
mDisplayMatrix = new Matrix();
float[] dims = { mDisplayMetrics.widthPixels,
mDisplayMetrics.heightPixels };
int value = mDisplay.getRotation();
String hwRotation = SystemProperties.get("ro.sf.hwrotation", "0");
if (hwRotation.equals("270") || hwRotation.equals("90")) {
value = (value + 3) % 4;
}
float degrees = getDegreesForRotation(value);
boolean requiresRotation = (degrees > 0);
if (requiresRotation) {
// Get the dimensions of the device in its native orientation
mDisplayMatrix.reset();
mDisplayMatrix.preRotate(-degrees);
mDisplayMatrix.mapPoints(dims);
dims[0] = Math.abs(dims[0]);
dims[1] = Math.abs(dims[1]);
}
mScreenBitmap = Surface.screenshot((int) dims[0], (int) dims[1]);
if (requiresRotation) {
// Rotate the screenshot to the current orientation
Bitmap ss = Bitmap.createBitmap(mDisplayMetrics.widthPixels,
mDisplayMetrics.heightPixels, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(ss);
c.translate(ss.getWidth() / 2, ss.getHeight() / 2);
c.rotate(degrees);
c.translate(-dims[0] / 2, -dims[1] / 2);
c.drawBitmap(mScreenBitmap, 0, 0, null);
c.setBitmap(null);
mScreenBitmap = ss;
}
// If we couldn't take the screenshot, notify the user
if (mScreenBitmap == null) {
return;
}
// Optimizations
mScreenBitmap.setHasAlpha(false);
mScreenBitmap.prepareToDraw();
try {
saveBitmap(mScreenBitmap);
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
public void saveBitmap(Bitmap bitmap) throws IOException {
String imageDate = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss")
.format(new Date(System.currentTimeMillis()));
File file = new File("/mnt/sdcard/Pictures/"+imageDate+".png");
if(!file.exists()){
file.createNewFile();
}
FileOutputStream out;
try {
out = new FileOutputStream(file);
if (bitmap.compress(Bitmap.CompressFormat.PNG, 70, out)) {
out.flush();
out.close();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
</SPAN>
package org.winplus.ss;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.Display;
import android.view.Surface;
import android.view.WindowManager;
import android.os.SystemProperties;
public class SimpleScreenshotActivity extends Activity {
private Display mDisplay;
private WindowManager mWindowManager;
private DisplayMetrics mDisplayMetrics;
private Bitmap mScreenBitmap;
private Matrix mDisplayMatrix;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new Thread(new Runnable() {
@Override
public void run() {
takeScreenshot();
}
}).start();
}
private float getDegreesForRotation(int value) {
switch (value) {
case Surface.ROTATION_90:
return 360f - 90f;
case Surface.ROTATION_180:
return 360f - 180f;
case Surface.ROTATION_270:
return 360f - 270f;
}
return 0f;
}
private void takeScreenshot() {
mWindowManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
mDisplay = mWindowManager.getDefaultDisplay();
mDisplayMetrics = new DisplayMetrics();
mDisplay.getRealMetrics(mDisplayMetrics);
mDisplayMatrix = new Matrix();
float[] dims = { mDisplayMetrics.widthPixels,
mDisplayMetrics.heightPixels };
int value = mDisplay.getRotation();
String hwRotation = SystemProperties.get("ro.sf.hwrotation", "0");
if (hwRotation.equals("270") || hwRotation.equals("90")) {
value = (value + 3) % 4;
}
float degrees = getDegreesForRotation(value);
boolean requiresRotation = (degrees > 0);
if (requiresRotation) {
// Get the dimensions of the device in its native orientation
mDisplayMatrix.reset();
mDisplayMatrix.preRotate(-degrees);
mDisplayMatrix.mapPoints(dims);
dims[0] = Math.abs(dims[0]);
dims[1] = Math.abs(dims[1]);
}
mScreenBitmap = Surface.screenshot((int) dims[0], (int) dims[1]);
if (requiresRotation) {
// Rotate the screenshot to the current orientation
Bitmap ss = Bitmap.createBitmap(mDisplayMetrics.widthPixels,
mDisplayMetrics.heightPixels, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(ss);
c.translate(ss.getWidth() / 2, ss.getHeight() / 2);
c.rotate(degrees);
c.translate(-dims[0] / 2, -dims[1] / 2);
c.drawBitmap(mScreenBitmap, 0, 0, null);
c.setBitmap(null);
mScreenBitmap = ss;
}
// If we couldn't take the screenshot, notify the user
if (mScreenBitmap == null) {
return;
}
// Optimizations
mScreenBitmap.setHasAlpha(false);
mScreenBitmap.prepareToDraw();
try {
saveBitmap(mScreenBitmap);
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
public void saveBitmap(Bitmap bitmap) throws IOException {
String imageDate = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss")
.format(new Date(System.currentTimeMillis()));
File file = new File("/mnt/sdcard/Pictures/"+imageDate+".png");
if(!file.exists()){
file.createNewFile();
}
FileOutputStream out;
try {
out = new FileOutputStream(file);
if (bitmap.compress(Bitmap.CompressFormat.PNG, 70, out)) {
out.flush();
out.close();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
PS：1、需要在AndroidManifest.xml中加入代码：android:sharedUserId="android.uid.system"
2、由于调用了@hide的API，所以编译得时候请使用makefile编译。或者通过在Eclipse中添加Jar文件通过编译。
3、此代码只在Android4.0中使用过，2.3的就没去做测试了。

4 利用TakeScreenShotService截图

Android手机一般都自带有手机屏幕截图的功能：在手机任何界面（当然手机要是开机点亮状态），通过按组合键，屏幕闪一下，然后咔嚓一声，截图的照片会保存到当前手机的图库中，真是一个不错的功能！

以我手头的测试手机为例，是同时按电源键+音量下键来实现截屏，苹果手机则是电源键 + HOME键，小米手机是菜单键+音量下键，而HTC一般是按住电源键再按左下角的“主页”键。那么Android源码中使用组合键是如何实现屏幕截图功能呢？前段时间由于工作的原因仔细看了一下，这两天不忙，便把相关的知识点串联起来整理一下，分下面两部分简单分析下实现流程：

Android源码中对组合键的捕获。

Android源码中对按键的捕获位于文件PhoneWindowManager.java（alps\frameworks\base\policy\src\com\android\internal\policy\impl）中，这个类处理所有的键盘输入事件，其中函数interceptKeyBeforeQueueing（）会对常用的按键做特殊处理。以我手头的测试机为例，是同时按电源键和音量下键来截屏，那么在这个函数中我们会看到这么两段代码：

.......

 case KeyEvent.KEYCODE_VOLUME_DOWN:

            case KeyEvent.KEYCODE_VOLUME_UP:

            case KeyEvent.KEYCODE_VOLUME_MUTE: {

                if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN) {

                    if (down) {

                        if (isScreenOn && !mVolumeDownKeyTriggered

                                && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {

                            mVolumeDownKeyTriggered = true;

                            mVolumeDownKeyTime = event.getDownTime();

                            mVolumeDownKeyConsumedByScreenshotChord = false;

                            cancelPendingPowerKeyAction();

                            interceptScreenshotChord();

                        }

                    } else {

                        mVolumeDownKeyTriggered = false;

                        cancelPendingScreenshotChordAction();

                    }

......

            case KeyEvent.KEYCODE_POWER: {

                result &= ~ACTION_PASS_TO_USER;

                if (down) {

                    if (isScreenOn && !mPowerKeyTriggered

                            && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {

                        mPowerKeyTriggered = true;

                        mPowerKeyTime = event.getDownTime();

                        interceptScreenshotChord();

                    }

......

可以看到正是在这里（响应Down事件）捕获是否按了音量下键和电源键的，而且两个地方都会进入函数interceptScreenshotChord()中，那么接下来看看这个函数干了什么工作：

    private void interceptScreenshotChord() {

        if (mVolumeDownKeyTriggered && mPowerKeyTriggered && !mVolumeUpKeyTriggered) {

            final long now = SystemClock.uptimeMillis();

            if (now <= mVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS

                    && now <= mPowerKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) {

                mVolumeDownKeyConsumedByScreenshotChord = true;

                cancelPendingPowerKeyAction();

                mHandler.postDelayed(mScreenshotChordLongPress,

                        ViewConfiguration.getGlobalActionKeyTimeout());

            }

        }

    }

在这个函数中，用两个布尔变量判断是否同时按了音量下键和电源键后，再计算两个按键响应Down事件之间的时间差不超过150毫秒，也就认为是同时按了这两个键后，算是真正的捕获到屏幕截屏的组合键。

附言：文件PhoneWindowManager.java类是拦截键盘消息的处理类，在此类中还有对home键、返回键等好多按键的处理。

Android源码中调用屏幕截图的接口。

捕获到组合键后，我们再看看android源码中是如何调用屏幕截图的函数接口。在上面的函数interceptScreenshotChord中我们看到用handler判断长按组合键500毫秒之后，会进入如下函数：

    private final Runnable mScreenshotChordLongPress = new Runnable() {

        public void run() {

            takeScreenshot();

        }

    };

在这里启动了一个线程来完成截屏的功能，接着看函数takeScreenshot():

private void takeScreenshot() {

        synchronized (mScreenshotLock) {

            if (mScreenshotConnection != null) {

                return;

            }

            ComponentName cn = new ComponentName("com.android.systemui",

                    "com.android.systemui.screenshot.TakeScreenshotService");

            Intent intent = new Intent();

            intent.setComponent(cn);

            ServiceConnection conn = new ServiceConnection() {

                @Override

                public void onServiceConnected(ComponentName name, IBinder service) {

                    synchronized (mScreenshotLock) {

                        if (mScreenshotConnection != this) {

                            return;

                        }

                        Messenger messenger = new Messenger(service);

                        Message msg = Message.obtain(null, 1);

                        final ServiceConnection myConn = this;

                        Handler h = new Handler(mHandler.getLooper()) {

                            @Override

                            public void handleMessage(Message msg) {

                                synchronized (mScreenshotLock) {

                                    if (mScreenshotConnection == myConn) {

                                        mContext.unbindService(mScreenshotConnection);

                                        mScreenshotConnection = null;

                                        mHandler.removeCallbacks(mScreenshotTimeout);

                                    }

                                }

                            }

                        };

                        msg.replyTo = new Messenger(h);

                        msg.arg1 = msg.arg2 = 0;

                        if (mStatusBar != null && mStatusBar.isVisibleLw())

                            msg.arg1 = 1;

                        if (mNavigationBar != null && mNavigationBar.isVisibleLw())

                            msg.arg2 = 1;

                        try {

                            messenger.send(msg);

                        } catch (RemoteException e) {

                        }

                    }

                }

                @Override

                public void onServiceDisconnected(ComponentName name) {}

            };

            if (mContext.bindService(intent, conn, Context.BIND_AUTO_CREATE)) {

                mScreenshotConnection = conn;

                mHandler.postDelayed(mScreenshotTimeout, 10000);

            }

        }

    }

可以看到这个函数使用AIDL绑定了service服务到"com.android.systemui.screenshot.TakeScreenshotService"，注意在service连接成功时，对message的msg.arg1和msg.arg2两个参数的赋值。其中在mScreenshotTimeout中对服务service做了超时处理。接着我们找到实现这个服务service的类TakeScreenshotService，看看其实现的流程：

public class TakeScreenshotService extends Service {

    private static final String TAG = "TakeScreenshotService";

    private static GlobalScreenshot mScreenshot;

    private Handler mHandler = new Handler() {

        @Override

        public void handleMessage(Message msg) {

            switch (msg.what) {

                case 1:

                    final Messenger callback = msg.replyTo;

                    if (mScreenshot == null) {

                        mScreenshot = new GlobalScreenshot(TakeScreenshotService.this);

                    }

                    mScreenshot.takeScreenshot(new Runnable() {

                        @Override public void run() {

                            Message reply = Message.obtain(null, 1);

                            try {

                                callback.send(reply);

                            } catch (RemoteException e) {

                            }

                        }

                    }, msg.arg1 > 0, msg.arg2 > 0);

            }

        }

    };

    @Override

    public IBinder onBind(Intent intent) {

        return new Messenger(mHandler).getBinder();

    }

}

在这个类中，我们主要看调用接口，用到了mScreenshot.takeScreenshot（）传递了三个参数，第一个是个runnable，第二和第三个是之前message传递的两个参数msg.arg1和msg.arg2。最后我们看看这个函数takeScreenshot()，位于文件GlobalScreenshot.java中（跟之前的函数重名但是文件路径不一样）：

 /**

     * Takes a screenshot of the current display and shows an animation.

     */

    void takeScreenshot(Runnable finisher, boolean statusBarVisible, boolean navBarVisible) {

        // We need to orient the screenshot correctly (and the Surface api seems to take screenshots

        // only in the natural orientation of the device :!)

        mDisplay.getRealMetrics(mDisplayMetrics);

        float[] dims = {mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels};

        float degrees = getDegreesForRotation(mDisplay.getRotation());

        boolean requiresRotation = (degrees > 0);

        if (requiresRotation) {

            // Get the dimensions of the device in its native orientation

            mDisplayMatrix.reset();

            mDisplayMatrix.preRotate(-degrees);

            mDisplayMatrix.mapPoints(dims);

            dims[0] = Math.abs(dims[0]);

            dims[1] = Math.abs(dims[1]);

        }

        // Take the screenshot

        mScreenBitmap = Surface.screenshot((int) dims[0], (int) dims[1]);

        if (mScreenBitmap == null) {

            notifyScreenshotError(mContext, mNotificationManager);

            finisher.run();

            return;

        }

        if (requiresRotation) {

            // Rotate the screenshot to the current orientation

            Bitmap ss = Bitmap.createBitmap(mDisplayMetrics.widthPixels,

                    mDisplayMetrics.heightPixels, Bitmap.Config.ARGB_8888);

            Canvas c = new Canvas(ss);

            c.translate(ss.getWidth() / 2, ss.getHeight() / 2);

            c.rotate(degrees);

            c.translate(-dims[0] / 2, -dims[1] / 2);

            c.drawBitmap(mScreenBitmap, 0, 0, null);

            c.setBitmap(null);

            mScreenBitmap = ss;

        }

        // Optimizations

        mScreenBitmap.setHasAlpha(false);

        mScreenBitmap.prepareToDraw();

        // Start the post-screenshot animation

        startAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,

                statusBarVisible, navBarVisible);

    }

这段代码的注释比较详细，其实看到这里，我们算是真正看到截屏的操作了，具体的工作包括对屏幕大小、旋转角度的获取，然后调用Surface类的screenshot方法截屏保存到bitmap中，之后把这部分位图填充到一个画布上，最后再启动一个延迟的拍照动画效果。如果再往下探究screenshot方法，发现已经是一个native方法了：

    /**

     * Like {@link #screenshot(int, int, int, int)} but includes all

     * Surfaces in the screenshot.

     *

     * @hide

     */

    public static native Bitmap screenshot(int width, int height);

使用JNI技术调用底层的代码，如果再往下走，会发现映射这这个jni函数在文件android_view_Surface.cpp中，这个真的已经是底层c++语言了，统一调用的底层函数是：

static jobject doScreenshot(JNIEnv* env, jobject clazz, jint width, jint height,

        jint minLayer, jint maxLayer, bool allLayers)

{

    ScreenshotPixelRef* pixels = new ScreenshotPixelRef(NULL);

    if (pixels->update(width, height, minLayer, maxLayer, allLayers) != NO_ERROR) {

        delete pixels;

        return 0;

    }

    uint32_t w = pixels->getWidth();

    uint32_t h = pixels->getHeight();

    uint32_t s = pixels->getStride();

    uint32_t f = pixels->getFormat();

    ssize_t bpr = s * android::bytesPerPixel(f);

    SkBitmap* bitmap = new SkBitmap();

    bitmap->setConfig(convertPixelFormat(f), w, h, bpr);

    if (f == PIXEL_FORMAT_RGBX_8888) {

        bitmap->setIsOpaque(true);

    }

    if (w > 0 && h > 0) {

        bitmap->setPixelRef(pixels)->unref();

        bitmap->lockPixels();

    } else {

        // be safe with an empty bitmap.

        delete pixels;

        bitmap->setPixels(NULL);

    }

    return GraphicsJNI::createBitmap(env, bitmap, false, NULL);

}

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