通常未通过特殊定制的 Android 系统，截屏都是经过同时按住音量下键和电源键来截屏。本篇文章就只讨论使用这些特殊按键来进行截屏。
这里我们就要明白事件是在哪里进行分发拦截的。通过源码的分析，我们发现是在PhoneWindowManager.java 中。
PhoneWindowManager#interceptKeyBeforeQueueing()
// frameworks\base\services\core\java\com\android\server\policy\PhoneWindowManager.java @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; } // 省略部分代码...... // Handle special keys. switch (keyCode) { ...... case KeyEvent.KEYCODE_VOLUME_DOWN: case KeyEvent.KEYCODE_VOLUME_UP: case KeyEvent.KEYCODE_VOLUME_MUTE: { // 按下音量键调用 handleVolumeKey(event, policyFlags); ...... break; } ...... case KeyEvent.KEYCODE_POWER: { ...... if (down) { // 按下电源键将调用 interceptPowerKeyDown(event, interactive); } else { interceptPowerKeyUp(event, interactive, canceled); } break; } } return result; }
1、电源键处理
PhoneWindowManager#interceptPowerKeyDown()
// PhoneWindowManager.java private void interceptPowerKeyDown(KeyEvent event, boolean interactive) { // 省略部分代码...... // Latch power key state to detect screenshot chord. if (interactive && !mScreenshotChordPowerKeyTriggered && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) { // power键按下的标志 mScreenshotChordPowerKeyTriggered = true; // 获取 Power 键的触发时间 mScreenshotChordPowerKeyTime = event.getDownTime(); // 处理屏幕截图事件 interceptScreenshotChord(); // 这个方法应该是消耗、拦截事件的，避免改变音量、铃声等。 interceptRingerToggleChord(); } // 省略部分代码...... }
interceptScreenshotChord()该方法下面再说，先介绍电源按键、音量按键的处理。
2、音量键处理
PhoneWindowManager#handleVolumeKey()
// PhoneWindowManager.java public void handleVolumeKey(KeyEvent event, int policyFlags) { final boolean down = event.getAction() == KeyEvent.ACTION_DOWN; final int keyCode = event.getKeyCode(); final boolean interactive = (policyFlags & FLAG_INTERACTIVE) != 0; if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN) { if (down) { // Any activity on the vol down button stops the ringer toggle shortcut cancelPendingRingerToggleChordAction(); if (interactive && !mScreenshotChordVolumeDownKeyTriggered && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) { // Volume键按下的标志 mScreenshotChordVolumeDownKeyTriggered = true; // 获取 Volume 键的触发时间 mScreenshotChordVolumeDownKeyTime = event.getDownTime(); // 赋值 false 该属性为了防止截屏的时候音量下键生效出现调节音量的 dialog 状态值 mScreenshotChordVolumeDownKeyConsumed = false; // 防止触发 Power 键长按功能 cancelPendingPowerKeyAction(); //处理屏幕截图事件 interceptScreenshotChord(); // 拦截相关快捷键 interceptAccessibilityShortcutChord(); } } else { // 省略部分代码...... } } else if (keyCode == KeyEvent.KEYCODE_VOLUME_UP) { // 省略部分代码...... } return; }
3、截屏事件处理 interceptScreenshotChord()
PhoneWindowManager#interceptScreenshotChord()
// PhoneWindowManager.java private void interceptScreenshotChord() { /* * if 判断参数介绍 * mScreenshotChordEnabled 其值为mContext.getResources().getBoolean(com.android.internal.R.bool.config_enableScreenshotChord); * mScreenshotChordVolumeDownKeyTriggered 音量下键按下时值为true * mScreenshotChordPowerKeyTriggered 电源键按下时值为true * mA11yShortcutChordVolumeUpKeyTriggered 音量上(加)键抬起时为false , 按下时为true **/ if (mScreenshotChordEnabled && mScreenshotChordVolumeDownKeyTriggered && mScreenshotChordPowerKeyTriggered && !mA11yShortcutChordVolumeUpKeyTriggered) { // 获取当前时间 final long now = SystemClock.uptimeMillis(); // 当前时间小于 音量下键按下时间 + 150ms // 当前时间小于 power键按下时间 + 150ms if (now <= mScreenshotChordVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS && now <= mScreenshotChordPowerKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) { boolean inLongScreenshot = Settings.System.getIntForUser(mContext.getContentResolver(), LONGSCREENSHOT_SETTING, 0, UserHandle.USER_CURRENT_OR_SELF) == 1; if (hasInPowerUtrlSavingMode() || inLongScreenshot) { return; } // 长按音量下键，达到截屏条件，将该事件消费掉。 mScreenshotChordVolumeDownKeyConsumed = true; // 防止触发 Power 键长按功能 cancelPendingPowerKeyAction(); // 设置截图的类型，TAKE_SCREENSHOT_FULLSCREEN 为全屏 mScreenshotRunnable.setScreenshotType(TAKE_SCREENSHOT_FULLSCREEN); // 截图的方式，(例如：按键、三指下滑 等等) mScreenshotRunnable.setScreenshotSource(SCREENSHOT_KEY_CHORD); //执行 mScreenshotRunnable mHandler.postDelayed(mScreenshotRunnable, getScreenshotChordLongPressDelay()); } } }
继续查看ScreenshotRunnable，此时会一步步向下调用，最终到SystemUI。
// PhoneWindowManager.java private class ScreenshotRunnable implements Runnable { private int mScreenshotType = TAKE_SCREENSHOT_FULLSCREEN; private int mScreenshotSource = SCREENSHOT_KEY_OTHER; public void setScreenshotType(int screenshotType) { mScreenshotType = screenshotType; } public void setScreenshotSource(int screenshotSource) { mScreenshotSource = screenshotSource; } @Override public void run() { // 回调到 DisplayPolicy.java mDefaultDisplayPolicy.takeScreenshot(mScreenshotType, mScreenshotSource); } }
DisplayPolicy#takeScreenshot()
// DisplayPolicy.java // 请求截取屏幕截图 public void takeScreenshot(int screenshotType, int source) { if (mScreenshotHelper != null) { mScreenshotHelper.takeScreenshot(screenshotType, mStatusBar != null && mStatusBar.isVisibleLw(), mNavigationBar != null && mNavigationBar.isVisibleLw(), source, mHandler, null /* completionConsumer */); } }
继续往下看ScreenshotHelper#takeScreenshot()
// ScreenshotHelper.java // 请求截取屏幕截图 public void takeScreenshot(final int screenshotType, final boolean hasStatus, final boolean hasNav, int source, @NonNull Handler handler, @Nullable Consumer<Uri> completionConsumer) { ScreenshotRequest screenshotRequest = new ScreenshotRequest(source, hasStatus, hasNav); takeScreenshot(screenshotType, SCREENSHOT_TIMEOUT_MS, handler, screenshotRequest, completionConsumer); } //到了 Binder调用环节, 此为客户端, 服务端为SystemUI中的 TakeScreenshotService private void takeScreenshot(final int screenshotType, long timeoutMs, @NonNull Handler handler, ScreenshotRequest screenshotRequest, @Nullable Consumer<Uri> completionConsumer) { synchronized (mScreenshotLock) { final Runnable mScreenshotTimeout = () -> { synchronized (mScreenshotLock) { if (mScreenshotConnection != null) { // 在获取屏幕截图捕获响应之前超时 Log.e(TAG, "Timed out before getting screenshot capture response"); // 重置连接 resetConnection(); // 通知截屏错误 notifyScreenshotError(); } } if (completionConsumer != null) { completionConsumer.accept(null); } }; Message msg = Message.obtain(null, screenshotType, screenshotRequest); Handler h = new Handler(handler.getLooper()) { @Override public void handleMessage(Message msg) { switch (msg.what) { case SCREENSHOT_MSG_URI: if (completionConsumer != null) { completionConsumer.accept((Uri) msg.obj); } handler.removeCallbacks(mScreenshotTimeout); break; case SCREENSHOT_MSG_PROCESS_COMPLETE: synchronized (mScreenshotLock) { resetConnection(); } break; } } }; msg.replyTo = new Messenger(h); if (mScreenshotConnection == null || mScreenshotService == null) { // 一个标准的Service连接 // config_screenshotServiceComponent == com.android.systemui/com.android.systemui.screenshot.TakeScreenshotService final ComponentName serviceComponent = ComponentName.unflattenFromString( mContext.getResources().getString( com.android.internal.R.string.config_screenshotServiceComponent)); final Intent serviceIntent = new Intent(); serviceIntent.setComponent(serviceComponent); ServiceConnection conn = new ServiceConnection() { @Override // 当Service连接成功之后 public void onServiceConnected(ComponentName name, IBinder service) { synchronized (mScreenshotLock) { if (mScreenshotConnection != this) { return; } mScreenshotService = service; Messenger messenger = new Messenger(mScreenshotService); try { messenger.send(msg); } catch (RemoteException e) { Log.e(TAG, "Couldn't take screenshot: " + e); if (completionConsumer != null) { completionConsumer.accept(null); } } } } @Override // 当Service断开连接时 public void onServiceDisconnected(ComponentName name) { synchronized (mScreenshotLock) { if (mScreenshotConnection != null) { resetConnection(); // only log an error if we're still within the timeout period if (handler.hasCallbacks(mScreenshotTimeout)) { handler.removeCallbacks(mScreenshotTimeout); notifyScreenshotError(); } } } } }; // bindService if (mContext.bindServiceAsUser(serviceIntent, conn, Context.BIND_AUTO_CREATE | Context.BIND_FOREGROUND_SERVICE, UserHandle.CURRENT)) { mScreenshotConnection = conn; handler.postDelayed(mScreenshotTimeout, timeoutMs); } } else { // 如果已经连接则直接发送Message Messenger messenger = new Messenger(mScreenshotService); try { messenger.send(msg); } catch (RemoteException e) { Log.e(TAG, "Couldn't take screenshot: " + e); if (completionConsumer != null) { completionConsumer.accept(null); } } handler.postDelayed(mScreenshotTimeout, timeoutMs); } } }
客户端通过向服务端发送 message 来将截屏任务交给 service，由 service 处理后面的操作。
// TakeScreenshotService.java private Handler mHandler = new Handler(Looper.myLooper()) { @Override public void handleMessage(Message msg) { // 获取客户端传的 Messenger 对象 final Messenger callback = msg.replyTo; Consumer<Uri> uriConsumer = uri -> { Message reply = Message.obtain(null, SCREENSHOT_MSG_URI, uri); try { / /Messenger 双向通信，在服务端用远程客户端的 Messenger 对象给客户端发送信息 callback.send(reply); } catch (RemoteException e) { } }; Runnable onComplete = () -> { Message reply = Message.obtain(null, SCREENSHOT_MSG_PROCESS_COMPLETE); try { callback.send(reply); } catch (RemoteException e) { } }; // 判断用户的设备是否为解锁状态 // 如果用户的存储被锁定，我们没有地方存储截图，所以跳过它，而不是显示一个误导性的动画和错误通知。 if (!mUserManager.isUserUnlocked()) { Log.w(TAG, "Skipping screenshot because storage is locked!"); post(() -> uriConsumer.accept(null)); post(onComplete); return; } ScreenshotHelper.ScreenshotRequest screenshotRequest = (ScreenshotHelper.ScreenshotRequest) msg.obj; mUiEventLogger.log(ScreenshotEvent.getScreenshotSource(screenshotRequest.getSource())); switch (msg.what) { case WindowManager.TAKE_SCREENSHOT_FULLSCREEN: // 全屏截图 // 我们在PhoneWindowManager传入的type为全屏截图,所以需要执行全屏截图流程 mScreenshot.takeScreenshot(uriConsumer, onComplete); break; case WindowManager.TAKE_SCREENSHOT_SELECTED_REGION: // 区域截图 mScreenshot.takeScreenshot(uriConsumer, onComplete); break; case WindowManager.TAKE_SCREENSHOT_PROVIDED_IMAGE: Bitmap screenshot = BitmapUtil.bundleToHardwareBitmap( screenshotRequest.getBitmapBundle()); Rect screenBounds = screenshotRequest.getBoundsInScreen(); Insets insets = screenshotRequest.getInsets(); int taskId = screenshotRequest.getTaskId(); int userId = screenshotRequest.getUserId(); ComponentName topComponent = screenshotRequest.getTopComponent(); mScreenshot.handleImageAsScreenshot(screenshot, screenBounds, insets, taskId, userId, topComponent, uriConsumer, onComplete); break; default: Log.d(TAG, "Invalid screenshot option: " + msg.what); } } };
TakeScreenshotService调用GlobalScreenshot.java的takeScreenshot()；
GlobalScreenshot#takeScreenshot()
// GlobalScreenshot.java /** *截取当前显示的屏幕截图并显示动画。. */ private void takeScreenshot(Consumer<Uri> finisher, Rect crop) { // copy the input Rect, since SurfaceControl.screenshot can mutate it Rect screenRect = new Rect(crop); int rot = mDisplay.getRotation(); int width = crop.width(); int height = crop.height(); takeScreenshot(SurfaceControl.screenshot(crop, width, height, rot), finisher, screenRect, Insets.NONE, true); } private void takeScreenshot(Bitmap screenshot, Consumer<Uri> finisher, Rect screenRect, Insets screenInsets, boolean showFlash) { // 此方法会清除上一次的截图信息--连续截图行为 dismissScreenshot("new screenshot requested", true); mScreenBitmap = screenshot; if (mScreenBitmap == null) { // 如果没有Bitmap则报告错误信息 mNotificationsController.notifyScreenshotError( R.string.screenshot_failed_to_capture_text); finisher.accept(null); mOnCompleteRunnable.run(); return; } if (!isUserSetupComplete()) { // 用户设置尚未完成,不应该向用户展示 分享和编辑 , 只显示一个Toast并保存图片 saveScreenshotAndToast(finisher); return; } // Optimizations mScreenBitmap.setHasAlpha(false); mScreenBitmap.prepareToDraw(); onConfigChanged(mContext.getResources().getConfiguration()); if (mDismissAnimation != null && mDismissAnimation.isRunning()) { mDismissAnimation.cancel(); } // 获取焦点 setWindowFocusable(true); // 开始截图后动画 startAnimation(finisher, screenRect, screenInsets, showFlash); } /** * 截屏后开始动画 */ private void startAnimation(final Consumer<Uri> finisher, Rect screenRect, Insets screenInsets, boolean showFlash) { if (mScreenshotIng == false) {//unisoc: Modify for bug1360276 mScreenshotIng = true; // 如果开启了省电模式，显示 toast，以便有一些视觉提示已截取屏幕截图 PowerManager powerManager =(PowerManager) mContext . getSystemService (Context.POWER_SERVICE); if (powerManager.isPowerSaveMode()) { Toast.makeText(mContext, R.string.screenshot_saved_title, Toast.LENGTH_SHORT).show(); } mScreenshotHandler.post(() -> { if (!mScreenshotLayout.isAttachedToWindow()) { // mScreenshotLayout是截屏的缩略图的父View // mScreenshotLayout 在 GlobalScreenshot.java 的构造方法中初始化。对应布局文件：global_screenshot.xml mWindowManager.addView(mScreenshotLayout, mWindowLayoutParams); } // 动画相关的View mScreenshotAnimatedView.setImageDrawable( createScreenDrawable(mScreenBitmap, screenInsets)); setAnimatedViewSize(screenRect.width(), screenRect.height()); // 显示动画何时开始 mScreenshotAnimatedView.setVisibility(View.GONE); //缩略图显示的View,将native层返回的Bitmap加载到此View上 mScreenshotPreview.setImageDrawable(createScreenDrawable(mScreenBitmap, screenInsets)); // 使静态预览不可见（消失），以便我们可以在屏幕上查询其位置 mScreenshotPreview.setVisibility(View.INVISIBLE); mScreenshotHandler.post(() -> { mScreenshotLayout.getViewTreeObserver().addOnComputeInternalInsetsListener(this); // 创建动画 mScreenshotAnimation = createScreenshotDropInAnimation(screenRect, showFlash); // 保存截图 saveScreenshotInWorkerThread(finisher, new ActionsReadyListener () { @Override void onActionsReady (SavedImageData imageData) { showUiOnActionsReady(imageData); mScreenshotIng = false; } }); // 播放快门声音以通知我们已截屏 mCameraSound.play(MediaActionSound.SHUTTER_CLICK); if (mScreenshotPreview.isAttachedToWindow()) { mScreenshotPreview.setLayerType(View.LAYER_TYPE_HARDWARE, null); mScreenshotPreview.buildLayer(); } // 开始执行动画 mScreenshotAnimation.start(); }); }); } } /** * 创建一个新的工作线程并将屏幕截图保存到媒体存储 */ private void saveScreenshotInWorkerThread( Consumer<Uri> finisher, @Nullable ActionsReadyListener actionsReadyListener) { SaveImageInBackgroundData data = new SaveImageInBackgroundData(); data.image = mScreenBitmap; // native 层返回的 Bitmap data.finisher = finisher; data.mActionsReadyListener = actionsReadyListener; if (mSaveInBgTask != null) { // just log success/failure for the pre-existing screenshot // 只需记录预先存在的屏幕截图的成功失败 mSaveInBgTask.setActionsReadyListener(new ActionsReadyListener() { @Override void onActionsReady(SavedImageData imageData) { logSuccessOnActionsReady(imageData); } }); } // 截图的一些信息存储在 SaveImageInBackgroundTask 中构建 mSaveInBgTask = new SaveImageInBackgroundTask(mContext, data); mSaveInBgTask.execute(); }
到此截屏流程完毕,可以查看下截图的View的xml文件：global_screenshot.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/global_screenshot_frame" android:layout_width="match_parent" android:layout_height="match_parent"> <ImageView android:id="@+id/global_screenshot_actions_background" android:layout_height="@dimen/screenshot_bg_protection_height" android:layout_width="match_parent" android:layout_gravity="bottom" android:alpha="0.0" android:src="@drawable/screenshot_actions_background_protection"/> <!--截屏动画相关的View --> <ImageView android:id="@+id/global_screenshot_animated_view" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="top|start" android:visibility="gone" android:elevation="@dimen/screenshot_preview_elevation" android:background="@drawable/screenshot_rounded_corners" /> <ImageView android:id="@+id/global_screenshot_flash" android:layout_width="match_parent" android:layout_height="match_parent" android:visibility="gone" android:elevation="@dimen/screenshot_preview_elevation" android:src="@android:color/white"/> <com.android.systemui.screenshot.ScreenshotSelectorView android:id="@+id/global_screenshot_selector" android:layout_width="match_parent" android:layout_height="match_parent" android:visibility="gone" android:pointerIcon="crosshair"/> <!-- 此处包含了一个layout, 而缩略图的View就在此layout中， 截屏右上角的关闭缩略图按钮 也在此layout中 --> <include layout="@layout/global_screenshot_static"/> </FrameLayout>
