Android8.1 MTK平台 截屏功能分析
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:0
system_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 = false
system_process D/WindowManager: interceptKeyTi keyCode=25 down=false repeatCount=0 keyguardOn=false mHomePressed=false canceled=false metaState:0
system_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} */
@Override
public 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 keyguard
return (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;
}
@Override
public 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() {
@Override
public 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()) {
@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) {
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() {
@Override
public void handleMessage(Message msg) {
final Messenger callback = msg.replyTo;
Runnable finisher = new Runnable() {
@Override
public 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;
}
}
};
@Override
public IBinder onBind(Intent intent) {
return new Messenger(mHandler).getBinder();
}
@Override
public 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 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 = 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 orientation
Bitmap 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 bitmap
mScreenBitmap.recycle();
mScreenBitmap = ss;
}
if (width != mDisplayMetrics.widthPixels || height != mDisplayMetrics.heightPixels) {
// Crop the screenshot to selected region
Bitmap cropped = Bitmap.createBitmap(mScreenBitmap, x, y, width, height);
mScreenBitmap.recycle();
mScreenBitmap = cropped;
}
// Optimizations
mScreenBitmap.setHasAlpha(false);
mScreenBitmap.prepareToDraw();
// Start the post-screenshot animation
startAnimation(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 parameter
IBinder 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 animation
mScreenshotView.setImageBitmap(mScreenBitmap);
mScreenshotLayout.requestFocus();
// Setup the animation with the screenshot just taken
if (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() {
@Override
public void onAnimationEnd(Animator animation) {
// Save the screenshot once we have a bit of time now
saveScreenshotInWorkerThread(finisher);
mWindowManager.removeView(mScreenshotLayout);
// Clear any references to the bitmap
mScreenBitmap = null;
mScreenshotView.setImageBitmap(null);
}
});
mScreenshotLayout.post(new Runnable() {
@Override
public void run() {
// Play the shutter sound to notify that we've taken a screenshot
mCameraSound.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());
}
@Override
protected 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 exist
mScreenshotDir.mkdirs();
// media provider uses seconds for DATE_MODIFIED and DATE_ADDED, but milliseconds
// for DATE_TAKEN
long dateSeconds = mImageTime / 1000;
// Save
OutputStream out = new FileOutputStream(mImageFilePath);
image.compress(Bitmap.CompressFormat.PNG, 100, out);
out.flush();
out.close();
// Save the screenshot to the MediaStore
ContentValues 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 intent
String 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 notification
PendingIntent 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
// mounted
Slog.e(TAG, "unable to save screenshot", e);
mParams.clearImage();
mParams.errorMsgResId = R.string.screenshot_failed_to_save_text;
}
// Recycle the bitmap data
if (image != null) {
image.recycle();
}
return null;
}
@Override
protected void onPostExecute(Void params) {
if (mParams.errorMsgResId != 0) {
// Show a message that we've failed to save the image to disk
GlobalScreenshot.notifyScreenshotError(mParams.context, mNotificationManager,
mParams.errorMsgResId);
} else {
// Show the final notification to indicate screenshot saved
Context context = mParams.context;
Resources r = context.getResources();
// Create the intent to show the screenshot in gallery
Intent 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 notification
mPublicNotificationBuilder
.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();
}
@Override
protected 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 notification
mNotificationManager.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
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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
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通过一系列的调用启动 TakeScreenshotService 服务，并通过其执行截屏的操作。
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具体的截屏代码是在 native 层实现的。
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截屏操作时候，若截屏失败则直接发送截屏失败的 notification 通知。
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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
