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Android中使用代码截图的各种方法总结

2015-01-13 11:55 531 查看

http://blog.csdn.net/woshinia/article/details/11520403

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）：

HelloAndroid.java实现代码为：

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 := platform2).修改AndroidManifest.xml 文件，添加
权限<uses-permissionandroid:name="android.permission.READ_FRAME_BUFFER"/>

2 基于Android ddmlib进行截屏

[java] view
plaincopypublic class ScreenShot {private BufferedImage image = null;/*** @param args*/public static void main(String[] args) {// TODO Auto-generated method stubAndroidDebugBridge.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 blocke.printStackTrace();}}}public void getScreenShot(IDevice device,String filename) {RawImage rawScreen = null;try {rawScreen = device.getScreenshot();} catch (TimeoutException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (AdbCommandRejectedException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.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);elseimage.setRGB(x, y, value);}}try {ImageIO.write((RenderedImage) image, "PNG", new File("D:/"+ filename + ".jpg"));} catch (IOException e) {// TODO Auto-generated catch blocke.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 blocke.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）[java] view
plaincopy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;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);new Thread(new Runnable() {@Overridepublic 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 orientationmDisplayMatrix.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 orientationBitmap 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 userif (mScreenBitmap == null) {return;}// OptimizationsmScreenBitmap.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;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);new Thread(new Runnable() {@Overridepublic 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 orientationmDisplayMatrix.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 orientationBitmap 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 userif (mScreenBitmap == null) {return;}// OptimizationsmScreenBitmap.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);
}

由于对C++不熟，我这里就不敢多言了。其实到这里，算是对手机android源码中通过组合键屏幕截图的整个流程有个大体了解了，一般我们在改动中熟悉按键的捕获原理，并且清楚调用的截屏函数接口即可，如果有兴趣的，可以继续探究更深的底层是如何实现的。应用

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