Android中使用代码截图的各种方法总结

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）：

<? xml version = "1.0" encoding = "utf-8" ?> < LinearLayout xmlns: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：

package com.example.helloandroid; import java.io.FileOutputStream; import java.text.SimpleDateFormat; import java.util.Date; import java.util.Locale; import android.app.Activity; import android.graphics.Bitmap; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; public class HelloAndroid extends Activity { private Button button; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); this .setContentView(R.layout.main); this .button = (Button) this .findViewById(R.id.my_button); this .button.setOnClickListener( new OnClickListener() { public void onClick(View v) { SimpleDateFormat sdf = new SimpleDateFormat( "yyyy-MM-dd_HH-mm-ss" , Locale.US); String fname = "/sdcard/" + sdf.format( new Date()) + ".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 = new FileOutputStream(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-permission android: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-permission android:name = "android.permission.READ_FRAME_BUFFER" />

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 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]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();         }     } }  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：

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....... 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：

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    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():

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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：

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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）：

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 /**     * 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：

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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