前言

涉及到的源码有

frameworks\base\services\core\java\com\android\server\policy\PhoneWindowManager.java

vendor\mediatek\proprietary\packages\apps\SystemUI\src\com\android\systemui\screenshot\TakeScreenshotService.java
vendor\mediatek\proprietary\packages\apps\SystemUI\src\com\android\systemui\screenshot\GlobalScreenshot.java

按键处理都是在 PhoneWindowManager 中，真正截屏的功能实现在 GlobalScreenshot 中， PhoneWindowManager 和 systemui 通过 bind TakeScreenshotService 来实现截屏功能

流程

一般未经过特殊定制的 Android 系统，截屏都是通过同时按住音量下键和电源键来截屏，后来我们使用的一些华为、oppo等厂商的系统你会发现可以通过三指滑动来截屏，下一篇我们会定制此功能，而且截屏显示风格类似 iphone 在左下角显示截屏缩略图，点击可跳转放大查看，3s 无操作后向左自动滑动消失。

好了，现在我们先来理一下系统截屏的流程

 system_process D/WindowManager: interceptKeyTi keyCode=25 down=true repeatCount=0 keyguardOn=false mHomePressed=false canceled=false metaState:0system_process D/WindowManager: interceptKeyTq keycode=25 interactive=true keyguardActive=false policyFlags=22000000 down =false canceled = false isWakeKey=false mVolumeDownKeyTriggered =true result = 1 useHapticFeedback = false isInjected = falsesystem_process D/WindowManager: interceptKeyTi keyCode=25 down=false repeatCount=0 keyguardOn=false mHomePressed=false canceled=false metaState:0system_process D/WindowManager: interceptKeyTq keycode=26 interactive=true keyguardActive=false policyFlags=22000000 down =false canceled = false isWakeKey=false mVolumeDownKeyTriggered =false result = 1 useHapticFeedback = false isInjected = false

上面是按下音量下键和电源键的日志，音量下键对应 keyCode=25 ，电源键对应 keyCode=26，来看到 PhoneWindowManager 中的 interceptKeyBeforeQueueing() 方法，在此处处理按键操作

 /** {@inheritDoc} */@Overridepublic int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {if (!mSystemBooted) {// If we have not yet booted, don't let key events do anything.return 0;}.....if (DEBUG_INPUT) {Log.d(TAG, "interceptKeyTq keycode=" + keyCode+ " interactive=" + interactive + " keyguardActive=" + keyguardActive+ " policyFlags=" + Integer.toHexString(policyFlags));}.....// Handle special keys.switch (keyCode) {.......case KeyEvent.KEYCODE_VOLUME_DOWN:case KeyEvent.KEYCODE_VOLUME_UP:case KeyEvent.KEYCODE_VOLUME_MUTE: {if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN) {if (down) {if (interactive && !mScreenshotChordVolumeDownKeyTriggered&& (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {mScreenshotChordVolumeDownKeyTriggered = true;mScreenshotChordVolumeDownKeyTime = event.getDownTime();mScreenshotChordVolumeDownKeyConsumed = false;cancelPendingPowerKeyAction();interceptScreenshotChord();interceptAccessibilityShortcutChord();}} else {mScreenshotChordVolumeDownKeyTriggered = false;cancelPendingScreenshotChordAction();cancelPendingAccessibilityShortcutAction();}} ....}

看到 KEYCODE_VOLUME_DOWN 中，记录当前按下音量下键的时间 mScreenshotChordVolumeDownKeyTime，cancelPendingPowerKeyAction() 移除电源键长按消息 MSG_POWER_LONG_PRESS，来看下核心方法 interceptScreenshotChord()

// Time to volume and power must be pressed within this interval of each other.
private static final long SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS = 150;private void interceptScreenshotChord() {if (mScreenshotChordEnabled&& mScreenshotChordVolumeDownKeyTriggered && mScreenshotChordPowerKeyTriggered&& !mA11yShortcutChordVolumeUpKeyTriggered) {final long now = SystemClock.uptimeMillis();if (now <= mScreenshotChordVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS&& now <= mScreenshotChordPowerKeyTime+ SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) {mScreenshotChordVolumeDownKeyConsumed = true;cancelPendingPowerKeyAction();mScreenshotRunnable.setScreenshotType(TAKE_SCREENSHOT_FULLSCREEN);mHandler.postDelayed(mScreenshotRunnable, getScreenshotChordLongPressDelay());}}}

只有当电源键按下时 mScreenshotChordPowerKeyTriggered 才为 true, 当两个按键的按下时间都大于 150 时，延时执行截屏任务 mScreenshotRunnable

private long getScreenshotChordLongPressDelay() {if (mKeyguardDelegate.isShowing()) {// Double the time it takes to take a screenshot from the keyguardreturn (long) (KEYGUARD_SCREENSHOT_CHORD_DELAY_MULTIPLIER *ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());}return ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout();}

若当前输入框是打开状态，则延时时间为输入框关闭时间加上系统配置的按键超时时间，若当前输入框没有打开则直接是系统配置的按键超时处理时间

紧接着看下 mScreenshotRunnable 都做了什么操作

private class ScreenshotRunnable implements Runnable {private int mScreenshotType = TAKE_SCREENSHOT_FULLSCREEN;public void setScreenshotType(int screenshotType) {mScreenshotType = screenshotType;}@Overridepublic void run() {takeScreenshot(mScreenshotType);}}private final ScreenshotRunnable mScreenshotRunnable = new ScreenshotRunnable();

可以看到在线程中调用了 takeScreenshot(),默认不设置截屏类型就是全屏，截屏类型有 TAKE_SCREENSHOT_SELECTED_REGION 选定的区域和 TAKE_SCREENSHOT_FULLSCREEN 全屏两种类型

// Assume this is called from the Handler thread.private void takeScreenshot(final int screenshotType) {synchronized (mScreenshotLock) {if (mScreenshotConnection != null) {return;}final ComponentName serviceComponent = new ComponentName(SYSUI_PACKAGE,SYSUI_SCREENSHOT_SERVICE);final Intent serviceIntent = new Intent();serviceIntent.setComponent(serviceComponent);ServiceConnection conn = new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {synchronized (mScreenshotLock) {if (mScreenshotConnection != this) {return;}Messenger messenger = new Messenger(service);Message msg = Message.obtain(null, screenshotType);final ServiceConnection myConn = this;Handler h = new Handler(mHandler.getLooper()) {@Overridepublic 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) {}}}@Overridepublic void onServiceDisconnected(ComponentName name) {synchronized (mScreenshotLock) {if (mScreenshotConnection != null) {mContext.unbindService(mScreenshotConnection);mScreenshotConnection = null;mHandler.removeCallbacks(mScreenshotTimeout);notifyScreenshotError();}}}};if (mContext.bindServiceAsUser(serviceIntent, conn,Context.BIND_AUTO_CREATE | Context.BIND_FOREGROUND_SERVICE_WHILE_AWAKE,UserHandle.CURRENT)) {mScreenshotConnection = conn;mHandler.postDelayed(mScreenshotTimeout, 10000);}}}

takeScreenshot 中通过 bind SystemUI中的 TakeScreenshotService 建立连接，连接成功后通过 Messenger 在两个进程中传递消息通行，有点类似 AIDL，关于 Messenger 的介绍可参考 Android进程间通讯之 messenger Messenger 主要传递当前的 mStatusBar 和 mNavigationBar 是否可见，再来看 TakeScreenshotService 中如何接收处理

public class TakeScreenshotService extends Service {private static final String TAG = "TakeScreenshotService";private static GlobalScreenshot mScreenshot;private Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {final Messenger callback = msg.replyTo;Runnable finisher = new Runnable() {@Overridepublic void run() {Message reply = Message.obtain(null, 1);try {callback.send(reply);} catch (RemoteException e) {}}};// If the storage for this user is locked, we have no place to store// the screenshot, so skip taking it instead of showing a misleading// animation and error notification.if (!getSystemService(UserManager.class).isUserUnlocked()) {Log.w(TAG, "Skipping screenshot because storage is locked!");post(finisher);return;}if (mScreenshot == null) {mScreenshot = new GlobalScreenshot(TakeScreenshotService.this);}switch (msg.what) {case WindowManager.TAKE_SCREENSHOT_FULLSCREEN:mScreenshot.takeScreenshot(finisher, msg.arg1 > 0, msg.arg2 > 0);break;case WindowManager.TAKE_SCREENSHOT_SELECTED_REGION:mScreenshot.takeScreenshotPartial(finisher, msg.arg1 > 0, msg.arg2 > 0);break;}}};@Overridepublic IBinder onBind(Intent intent) {return new Messenger(mHandler).getBinder();}@Overridepublic boolean onUnbind(Intent intent) {if (mScreenshot != null) mScreenshot.stopScreenshot();return true;}
}

可以看到通过 mHandler 接收传递的消息，获取截屏类型和是否要包含状态栏、导航栏，通过创建 GlobalScreenshot 对象(真正干活的来了），调用 takeScreenshot 执行截屏操作，继续跟进

 void takeScreenshot(Runnable finisher, boolean statusBarVisible, boolean navBarVisible) {mDisplay.getRealMetrics(mDisplayMetrics);takeScreenshot(finisher, statusBarVisible, navBarVisible, 0, 0, mDisplayMetrics.widthPixels,mDisplayMetrics.heightPixels);}/*** Takes a screenshot of the current display and shows an animation.*/void takeScreenshot(Runnable finisher, boolean statusBarVisible, boolean navBarVisible,int x, int y, int width, int height) {// 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 orientationmDisplayMatrix.reset();mDisplayMatrix.preRotate(-degrees);mDisplayMatrix.mapPoints(dims);dims[0] = Math.abs(dims[0]);dims[1] = Math.abs(dims[1]);}// Take the screenshotmScreenBitmap = SurfaceControl.screenshot((int) dims[0], (int) dims[1]);if (mScreenBitmap == null) {notifyScreenshotError(mContext, mNotificationManager,R.string.screenshot_failed_to_capture_text);finisher.run();return;}if (requiresRotation) {// Rotate the screenshot to the current orientationBitmap ss = Bitmap.createBitmap(mDisplayMetrics.widthPixels,mDisplayMetrics.heightPixels, Bitmap.Config.ARGB_8888,mScreenBitmap.hasAlpha(), mScreenBitmap.getColorSpace());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);// Recycle the previous bitmapmScreenBitmap.recycle();mScreenBitmap = ss;}if (width != mDisplayMetrics.widthPixels || height != mDisplayMetrics.heightPixels) {// Crop the screenshot to selected regionBitmap cropped = Bitmap.createBitmap(mScreenBitmap, x, y, width, height);mScreenBitmap.recycle();mScreenBitmap = cropped;}// OptimizationsmScreenBitmap.setHasAlpha(false);mScreenBitmap.prepareToDraw();// Start the post-screenshot animationstartAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,statusBarVisible, navBarVisible);}

获取屏幕的宽高和当前屏幕方向以确定是否需要旋转图片，然后通过 SurfaceControl.screenshot 截屏，好吧，再继续往下看到

public static Bitmap screenshot(int width, int height) {// TODO: should take the display as a parameterIBinder displayToken = SurfaceControl.getBuiltInDisplay(SurfaceControl.BUILT_IN_DISPLAY_ID_MAIN);return nativeScreenshot(displayToken, new Rect(), width, height, 0, 0, true,false, Surface.ROTATION_0);
}

这里调用的是 nativeScreenshot 方法，它是一个 native 方法，具体的实现在JNI层，这里就不做过多的介绍了。继续回到我们的 takeScreenshot 方法，在调用了截屏方法 screentshot 之后，判断是否截屏成功：
截屏失败则调用 notifyScreenshotError 发送通知。截屏成功，则调用 startAnimation 播放动画，来分析下动画，后面我们会改这个动画的效果

 /*** Starts the animation after taking the screenshot*/private void startAnimation(final Runnable finisher, int w, int h, boolean statusBarVisible,boolean navBarVisible) {// If power save is on, show a toast so there is some visual indication that a screenshot// has been taken.PowerManager powerManager = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);if (powerManager.isPowerSaveMode()) {Toast.makeText(mContext, R.string.screenshot_saved_title, Toast.LENGTH_SHORT).show();}// Add the view for the animationmScreenshotView.setImageBitmap(mScreenBitmap);mScreenshotLayout.requestFocus();// Setup the animation with the screenshot just takenif (mScreenshotAnimation != null) {if (mScreenshotAnimation.isStarted()) {mScreenshotAnimation.end();}mScreenshotAnimation.removeAllListeners();}mWindowManager.addView(mScreenshotLayout, mWindowLayoutParams);ValueAnimator screenshotDropInAnim = createScreenshotDropInAnimation();ValueAnimator screenshotFadeOutAnim = createScreenshotDropOutAnimation(w, h,statusBarVisible, navBarVisible);mScreenshotAnimation = new AnimatorSet();mScreenshotAnimation.playSequentially(screenshotDropInAnim, screenshotFadeOutAnim);mScreenshotAnimation.addListener(new AnimatorListenerAdapter() {@Overridepublic void onAnimationEnd(Animator animation) {// Save the screenshot once we have a bit of time nowsaveScreenshotInWorkerThread(finisher);mWindowManager.removeView(mScreenshotLayout);// Clear any references to the bitmapmScreenBitmap = null;mScreenshotView.setImageBitmap(null);}});mScreenshotLayout.post(new Runnable() {@Overridepublic void run() {// Play the shutter sound to notify that we've taken a screenshotmCameraSound.play(MediaActionSound.SHUTTER_CLICK);mScreenshotView.setLayerType(View.LAYER_TYPE_HARDWARE, null);mScreenshotView.buildLayer();mScreenshotAnimation.start();}});}

先判断是否是低电量模式，若是发出已抓取屏幕截图的 toast，然后通过 WindowManager 在屏幕中间添加一个装有截屏缩略图的 view，同时创建两个动画组合，通过 mCameraSound 播放截屏咔嚓声并执行动画，动画结束后移除刚刚添加的 view，同时调用 saveScreenshotInWorkerThread 保存图片到媒体库，我们直接来看 SaveImageInBackgroundTask

class SaveImageInBackgroundTask extends AsyncTask<Void, Void, Void> {.....SaveImageInBackgroundTask(Context context, SaveImageInBackgroundData data,NotificationManager nManager) {......mNotificationBuilder = new Notification.Builder(context, NotificationChannels.SCREENSHOTS).setTicker(r.getString(R.string.screenshot_saving_ticker)+ (mTickerAddSpace ? " " : "")).setContentTitle(r.getString(R.string.screenshot_saving_title)).setContentText(r.getString(R.string.screenshot_saving_text)).setSmallIcon(R.drawable.stat_notify_image).setWhen(now).setShowWhen(true).setColor(r.getColor(com.android.internal.R.color.system_notification_accent_color)).setStyle(mNotificationStyle).setPublicVersion(mPublicNotificationBuilder.build());mNotificationBuilder.setFlag(Notification.FLAG_NO_CLEAR, true);SystemUI.overrideNotificationAppName(context, mNotificationBuilder);mNotificationManager.notify(SystemMessage.NOTE_GLOBAL_SCREENSHOT,mNotificationBuilder.build());}@Overrideprotected Void doInBackground(Void... params) {if (isCancelled()) {return null;}// By default, AsyncTask sets the worker thread to have background thread priority, so bump// it back up so that we save a little quicker.Process.setThreadPriority(Process.THREAD_PRIORITY_FOREGROUND);Context context = mParams.context;Bitmap image = mParams.image;Resources r = context.getResources();try {// Create screenshot directory if it doesn't existmScreenshotDir.mkdirs();// media provider uses seconds for DATE_MODIFIED and DATE_ADDED, but milliseconds// for DATE_TAKENlong dateSeconds = mImageTime / 1000;// SaveOutputStream out = new FileOutputStream(mImageFilePath);image.compress(Bitmap.CompressFormat.PNG, 100, out);out.flush();out.close();// Save the screenshot to the MediaStoreContentValues values = new ContentValues();ContentResolver resolver = context.getContentResolver();values.put(MediaStore.Images.ImageColumns.DATA, mImageFilePath);values.put(MediaStore.Images.ImageColumns.TITLE, mImageFileName);values.put(MediaStore.Images.ImageColumns.DISPLAY_NAME, mImageFileName);values.put(MediaStore.Images.ImageColumns.DATE_TAKEN, mImageTime);values.put(MediaStore.Images.ImageColumns.DATE_ADDED, dateSeconds);values.put(MediaStore.Images.ImageColumns.DATE_MODIFIED, dateSeconds);values.put(MediaStore.Images.ImageColumns.MIME_TYPE, "image/png");values.put(MediaStore.Images.ImageColumns.WIDTH, mImageWidth);values.put(MediaStore.Images.ImageColumns.HEIGHT, mImageHeight);values.put(MediaStore.Images.ImageColumns.SIZE, new File(mImageFilePath).length());Uri uri = resolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values);// Create a share intentString subjectDate = DateFormat.getDateTimeInstance().format(new Date(mImageTime));String subject = String.format(SCREENSHOT_SHARE_SUBJECT_TEMPLATE, subjectDate);Intent sharingIntent = new Intent(Intent.ACTION_SEND);sharingIntent.setType("image/png");sharingIntent.putExtra(Intent.EXTRA_STREAM, uri);sharingIntent.putExtra(Intent.EXTRA_SUBJECT, subject);// Create a share action for the notification. Note, we proxy the call to ShareReceiver// because RemoteViews currently forces an activity options on the PendingIntent being// launched, and since we don't want to trigger the share sheet in this case, we will// start the chooser activitiy directly in ShareReceiver.PendingIntent shareAction = PendingIntent.getBroadcast(context, 0,new Intent(context, GlobalScreenshot.ShareReceiver.class).putExtra(SHARING_INTENT, sharingIntent),PendingIntent.FLAG_CANCEL_CURRENT);Notification.Action.Builder shareActionBuilder = new Notification.Action.Builder(R.drawable.ic_screenshot_share,r.getString(com.android.internal.R.string.share), shareAction);mNotificationBuilder.addAction(shareActionBuilder.build());// Create a delete action for the notificationPendingIntent deleteAction = PendingIntent.getBroadcast(context, 0,new Intent(context, GlobalScreenshot.DeleteScreenshotReceiver.class).putExtra(GlobalScreenshot.SCREENSHOT_URI_ID, uri.toString()),PendingIntent.FLAG_CANCEL_CURRENT | PendingIntent.FLAG_ONE_SHOT);Notification.Action.Builder deleteActionBuilder = new Notification.Action.Builder(R.drawable.ic_screenshot_delete,r.getString(com.android.internal.R.string.delete), deleteAction);mNotificationBuilder.addAction(deleteActionBuilder.build());mParams.imageUri = uri;mParams.image = null;mParams.errorMsgResId = 0;} catch (Exception e) {// IOException/UnsupportedOperationException may be thrown if external storage is not// mountedSlog.e(TAG, "unable to save screenshot", e);mParams.clearImage();mParams.errorMsgResId = R.string.screenshot_failed_to_save_text;}// Recycle the bitmap dataif (image != null) {image.recycle();}return null;}@Overrideprotected void onPostExecute(Void params) {if (mParams.errorMsgResId != 0) {// Show a message that we've failed to save the image to diskGlobalScreenshot.notifyScreenshotError(mParams.context, mNotificationManager,mParams.errorMsgResId);} else {// Show the final notification to indicate screenshot savedContext context = mParams.context;Resources r = context.getResources();// Create the intent to show the screenshot in galleryIntent launchIntent = new Intent(Intent.ACTION_VIEW);launchIntent.setDataAndType(mParams.imageUri, "image/png");launchIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_GRANT_READ_URI_PERMISSION);final long now = System.currentTimeMillis();// Update the text and the icon for the existing notificationmPublicNotificationBuilder.setContentTitle(r.getString(R.string.screenshot_saved_title)).setContentText(r.getString(R.string.screenshot_saved_text)).setContentIntent(PendingIntent.getActivity(mParams.context, 0, launchIntent, 0)).setWhen(now).setAutoCancel(true).setColor(context.getColor(com.android.internal.R.color.system_notification_accent_color));mNotificationBuilder.setContentTitle(r.getString(R.string.screenshot_saved_title)).setContentText(r.getString(R.string.screenshot_saved_text)).setContentIntent(PendingIntent.getActivity(mParams.context, 0, launchIntent, 0)).setWhen(now).setAutoCancel(true).setColor(context.getColor(com.android.internal.R.color.system_notification_accent_color)).setPublicVersion(mPublicNotificationBuilder.build()).setFlag(Notification.FLAG_NO_CLEAR, false);mNotificationManager.notify(SystemMessage.NOTE_GLOBAL_SCREENSHOT,mNotificationBuilder.build());}mParams.finisher.run();mParams.clearContext();}@Overrideprotected void onCancelled(Void params) {// If we are cancelled while the task is running in the background, we may get null params.// The finisher is expected to always be called back, so just use the baked-in params from// the ctor in any case.mParams.finisher.run();mParams.clearImage();mParams.clearContext();// Cancel the posted notificationmNotificationManager.cancel(SystemMessage.NOTE_GLOBAL_SCREENSHOT);}
}

简单说下， SaveImageInBackgroundTask 构造方法中做了大量的准备工作，截屏图片的时间命名格式、截屏通知对象创建，在 doInBackground 中将截屏图片通过 ContentResolver 存储至 MediaStore，再创建两个 PendingIntent，用于分享和删除截屏图片，在 onPostExecute 中发送刚刚创建的 Notification 至 statuBar 显示，到此截屏的流程就结束了。

其它

我们再回到 PhoneWindowManager 中看下，通过上面我们知道要想截屏只需通过如下两行代码即可

mScreenshotRunnable.setScreenshotType(TAKE_SCREENSHOT_FULLSCREEN);
mHandler.post(mScreenshotRunnable);

通过搜索上面的关键代码，我们发现还有另外两处也调用了截屏的代码，一起来看下

@Override
public long interceptKeyBeforeDispatching(WindowState win, KeyEvent event, int policyFlags) {final boolean keyguardOn = keyguardOn();final int keyCode = event.getKeyCode();.....else if (keyCode == KeyEvent.KEYCODE_S && event.isMetaPressed()&& event.isCtrlPressed()) {if (down && repeatCount == 0) {int type = event.isShiftPressed() ? TAKE_SCREENSHOT_SELECTED_REGION: TAKE_SCREENSHOT_FULLSCREEN;mScreenshotRunnable.setScreenshotType(type);mHandler.post(mScreenshotRunnable);return -1;}}....else if (keyCode == KeyEvent.KEYCODE_SYSRQ) {if (down && repeatCount == 0) {mScreenshotRunnable.setScreenshotType(TAKE_SCREENSHOT_FULLSCREEN);mHandler.post(mScreenshotRunnable);}return -1;}......}

也是在拦截按键消息分发之前的方法中，查看 KeyEvent 源码,第一种情况大概网上搜索了下，应该是接外设时，同时按下 S 键 + Meta键 + Ctrl键即可截屏，关于 Meta 介绍可参考Meta键始末第二种情况是按下截屏键时，对应 keyCode 为 120，可以用 adb shell input keyevent 120 模拟发现也能截屏

 /** Key code constant: 'S' key. */public static final int KEYCODE_S               = 47;/** Key code constant: System Request / Print Screen key. */public static final int KEYCODE_SYSRQ           = 120;

常用按键对应值

这样文章开头提到的三指截屏操作，我们就可以加在 PhoneWindowManager 中，当手势监听获取到三指时，只需调用截屏的两行代码即可

总结

在 PhoneWindowManager 的 dispatchUnhandledKey 方法中处理App无法处理的按键事件，当然也包括音量减少键和电源按键的组合按键
通过一系列的调用启动 TakeScreenshotService 服务，并通过其执行截屏的操作。
具体的截屏代码是在 native 层实现的。
截屏操作时候，若截屏失败则直接发送截屏失败的 notification 通知。
截屏之后，若截屏成功，则先执行截屏的动画，并在动画效果执行完毕之后，发送截屏成功的 notification 的通知。

参考文章

Android 截屏方法总结
Android KeyCode列表

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效果图修改位置 vendor\mediatek\proprietary\packages\apps\Dialer\java\com\android\incallui\video\impl\Video ...
Android8.1 MTK平台修改蓝牙默认名称
8.1 的默认蓝牙名称为 Android Bluedroid 通过搜索你会找到如下文件 device/generic/common/bluetooth/bdroid_buildcfg.h #ifnde ...
Android8.1 MTK 平台 Launcher3 修改定制
一.去掉默认 Google 搜索栏修改位置 vendor\mediatek\proprietary\packages\apps\Launcher3\src\com\android\launcher3 ...

Android8.1 MTK平台截屏功能分析

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Android8.1 MTK平台 截屏功能分析

前言

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Android8.1 MTK平台截屏功能分析

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