Android 截圖功能源碼的分析
Android 截圖功能源碼的分析
一般沒(méi)有修改rom的android原生系統(tǒng)截圖功能的組合鍵是音量減+開(kāi)機(jī)鍵；今天我們從源碼角度來(lái)分析截圖功能是如何在源碼中實(shí)現(xiàn)的。
在android系統(tǒng)中，由于我們的每一個(gè)Android界面都是一個(gè)Activity，而界面的顯示都是通過(guò)Window對(duì)象實(shí)現(xiàn)的，每個(gè)Window對(duì)象實(shí)際上都是PhoneWindow的實(shí)例，而每個(gè)PhoneWindow對(duì)象都對(duì)應(yīng)一個(gè)PhoneWindowManager對(duì)象，當(dāng)我們?cè)贏ctivity界面執(zhí)行按鍵操作的時(shí)候，在將按鍵的處理操作分發(fā)到App之前，首先會(huì)回調(diào)PhoneWindowManager中的dispatchUnhandledKey方法，該方法主要用于執(zhí)行當(dāng)前App處理按鍵之前的操作，我們具體看一下該方法的實(shí)現(xiàn)。
/** {@inheritDoc} */
@Override
public KeyEvent dispatchUnhandledKey(WindowState win, KeyEvent event, int policyFlags) {
...
KeyEvent fallbackEvent = null;
if ((event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
final KeyCharacterMap kcm = event.getKeyCharacterMap();
final int keyCode = event.getKeyCode();
final int metaState = event.getMetaState();
final boolean initialDown = event.getAction() == KeyEvent.ACTION_DOWN
&& event.getRepeatCount() == 0;
// Check for fallback actions specified by the key character map.
final FallbackAction fallbackAction;
if (initialDown) {
fallbackAction = kcm.getFallbackAction(keyCode, metaState);
} else {
fallbackAction = mFallbackActions.get(keyCode);
}
if (fallbackAction != null) {
...
final int flags = event.getFlags() | KeyEvent.FLAG_FALLBACK;
fallbackEvent = KeyEvent.obtain(
event.getDownTime(), event.getEventTime(),
event.getAction(), fallbackAction.keyCode,
event.getRepeatCount(), fallbackAction.metaState,
event.getDeviceId(), event.getScanCode(),
flags, event.getSource(), null);
if (!interceptFallback(win, fallbackEvent, policyFlags)) {
fallbackEvent.recycle();
fallbackEvent = null;
}
if (initialDown) {
mFallbackActions.put(keyCode, fallbackAction);
} else if (event.getAction() == KeyEvent.ACTION_UP) {
mFallbackActions.remove(keyCode);
fallbackAction.recycle();
}
}
}
...
return fallbackEvent;
}
這里我們關(guān)注一下方法體中調(diào)用的：interceptFallback方法，通過(guò)調(diào)用該方法將處理按鍵的操作下發(fā)到該方法中，我們繼續(xù)看一下該方法的實(shí)現(xiàn)邏輯。
private boolean interceptFallback(WindowState win, KeyEvent fallbackEvent, int policyFlags) {
int actions = interceptKeyBeforeQueueing(fallbackEvent, policyFlags);
if ((actions & ACTION_PASS_TO_USER) != 0) {
long delayMillis = interceptKeyBeforeDispatching(
win, fallbackEvent, policyFlags);
if (delayMillis == 0) {
return true;
}
}
return false;
}
然后我們看到在interceptFallback方法中我們調(diào)用了interceptKeyBeforeQueueing方法，通過(guò)閱讀我們我們知道該方法主要實(shí)現(xiàn)了對(duì)截屏按鍵的處理流程，這樣我們繼續(xù)看一下interceptKeyBeforeWueueing方法的處理：
@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;
}
...
// Handle special keys.
switch (keyCode) {
case KeyEvent.KEYCODE_VOLUME_DOWN:
case KeyEvent.KEYCODE_VOLUME_UP:
case KeyEvent.KEYCODE_VOLUME_MUTE: {
if (mUseTvRouting) {
// On TVs volume keys never go to the foreground app
result &= ~ACTION_PASS_TO_USER;
}
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();
}
} else {
mScreenshotChordVolumeDownKeyTriggered = false;
cancelPendingScreenshotChordAction();
}
}
...
return result;
}
可以發(fā)現(xiàn)這里首先判斷當(dāng)前系統(tǒng)是否已經(jīng)boot完畢，若尚未啟動(dòng)完畢，則所有的按鍵操作都將失效，若啟動(dòng)完成，則執(zhí)行后續(xù)的操作，這里我們只是關(guān)注音量減少按鍵和電源按鍵組合的處理事件。另外這里多說(shuō)一句想安卓系統(tǒng)的HOME按鍵事件，MENU按鍵事件，進(jìn)程列表按鍵事件等等都是在這里實(shí)現(xiàn)的，后續(xù)中我們會(huì)陸續(xù)介紹這方面的內(nèi)容。
回到我們的interceptKeyBeforeQueueing方法，當(dāng)我用按下音量減少按鍵的時(shí)候回進(jìn)入到：case KeyEvent.KEYCODE_VOLUME_MUTE分支并執(zhí)行相應(yīng)的邏輯，然后同時(shí)判斷用戶是否按下了電源鍵，若同時(shí)按下了電源鍵，則執(zhí)行：
if (interactive && !mScreenshotChordVolumeDownKeyTriggered
&& (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
mScreenshotChordVolumeDownKeyTriggered = true;
mScreenshotChordVolumeDownKeyTime = event.getDownTime();
mScreenshotChordVolumeDownKeyConsumed = false;
cancelPendingPowerKeyAction();
interceptScreenshotChord();
}
可以發(fā)現(xiàn)這里的interceptScreenshotChrod方法就是系統(tǒng)準(zhǔn)備開(kāi)始執(zhí)行截屏操作的開(kāi)始，我們繼續(xù)看一下interceptcreenshotChord方法的實(shí)現(xiàn)。
private void interceptScreenshotChord() {
if (mScreenshotChordEnabled
&& mScreenshotChordVolumeDownKeyTriggered && mScreenshotChordPowerKeyTriggered
&& !mScreenshotChordVolumeUpKeyTriggered) {
final long now = SystemClock.uptimeMillis();
if (now <= mScreenshotChordVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS
&& now <= mScreenshotChordPowerKeyTime
+ SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) {
mScreenshotChordVolumeDownKeyConsumed = true;
cancelPendingPowerKeyAction();
mHandler.postDelayed(mScreenshotRunnable, getScreenshotChordLongPressDelay());
}
}
}
在方法體中我們最終會(huì)執(zhí)行發(fā)送一個(gè)延遲的異步消息，請(qǐng)求執(zhí)行截屏的操作而這里的延時(shí)時(shí)間，若當(dāng)前輸入框是打開(kāi)狀態(tài)，則延時(shí)時(shí)間為輸入框關(guān)閉時(shí)間加上系統(tǒng)配置的按鍵超時(shí)時(shí)間，若當(dāng)前輸入框沒(méi)有打開(kāi)則直接是系統(tǒng)配置的按鍵超時(shí)處理時(shí)間，可看一下getScreenshotChordLongPressDelay方法的具體實(shí)現(xiàn)。
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();
}
回到我們的interceptScreenshotChord方法，發(fā)送了異步消息之后系統(tǒng)最終會(huì)被我們發(fā)送的Runnable對(duì)象的run方法執(zhí)行；這樣我們看一下Runnable類型的mScreenshotRunnable的run方法的實(shí)現(xiàn):
private final Runnable mScreenshotRunnable = new Runnable() {
@Override
public void run() {
takeScreenshot();
}
};
好吧，方法體中并未執(zhí)行其他操作，直接就是調(diào)用了takeScreenshot方法，這樣我們繼續(xù)看一下takeScreenshot方法的實(shí)現(xiàn)。
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.bindServiceAsUser(
intent, conn, Context.BIND_AUTO_CREATE, UserHandle.CURRENT)) {
mScreenshotConnection = conn;
mHandler.postDelayed(mScreenshotTimeout, 10000);
}
}
}
可以發(fā)現(xiàn)這里通過(guò)反射機(jī)制創(chuàng)建了一個(gè)TakeScreenshotService對(duì)象然后調(diào)用了bindServiceAsUser，這樣就創(chuàng)建了TakeScreenshotService服務(wù)并在服務(wù)創(chuàng)建之后發(fā)送了一個(gè)異步消息。好了，我們看一下TakeScreenshotService的實(shí)現(xiàn)邏輯。
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();
}
}
可以發(fā)現(xiàn)在在TakeScreenshotService類的定義中有一個(gè)Handler成員變量，而我們?cè)趩?dòng)TakeScreentshowService的時(shí)候回發(fā)送一個(gè)異步消息，這樣就會(huì)執(zhí)行mHandler的handleMessage方法，然后在handleMessage方法中我們創(chuàng)建了一個(gè)GlobalScreenshow對(duì)象，然后執(zhí)行了takeScreenshot方法，好吧，繼續(xù)看一下takeScreentshot方法的執(zhí)行邏輯。
/**
* 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 = SurfaceControl.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);
// Recycle the previous bitmap
mScreenBitmap.recycle();
mScreenBitmap = ss;
}
// Optimizations
mScreenBitmap.setHasAlpha(false);
mScreenBitmap.prepareToDraw();
// Start the post-screenshot animation
startAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,
statusBarVisible, navBarVisible);
}
可以看到這里后兩個(gè)參數(shù)：statusBarVisible，navBarVisible是否可見(jiàn)，而這兩個(gè)參數(shù)在我們
PhoneWindowManager.takeScreenshot方法傳遞的：
if (mStatusBar != null && mStatusBar.isVisibleLw())
msg.arg1 = 1;
if (mNavigationBar != null && mNavigationBar.isVisibleLw())
msg.arg2 = 1;
可見(jiàn)若果mStatusBar可見(jiàn)，則傳遞的statusBarVisible為true，若mNavigationBar可見(jiàn)，則傳遞的navBarVisible為true。然后我們?cè)诮仄恋臅r(shí)候判斷nStatusBar是否可見(jiàn)，mNavigationBar是否可見(jiàn)，若可見(jiàn)的時(shí)候則截屏同樣將其截屏出來(lái)。繼續(xù)回到我們的takeScreenshot方法，然后調(diào)用了：
// Take the screenshot mScreenBitmap = SurfaceControl.screenshot((int) dims[0], (int) dims[1]);
方法，看注釋，這里就是執(zhí)行截屏事件的具體操作了，然后我看一下SurfaceControl.screenshot方法的具體實(shí)現(xiàn)，另外這里需要注意的是，截屏之后返回的是一個(gè)Bitmap對(duì)象，其實(shí)熟悉android繪制機(jī)制的童鞋應(yīng)該知道android中所有顯示能夠顯示的東西，在內(nèi)存中表現(xiàn)都是Bitmap對(duì)象。
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);
}
好吧，這里調(diào)用的是nativeScreenshot方法，它是一個(gè)native方法，具體的實(shí)現(xiàn)在JNI層，這里就不做過(guò)多的介紹了。繼續(xù)回到我們的takeScreenshot方法，在調(diào)用了截屏方法screentshot之后，判斷是否截屏成功：
if (mScreenBitmap == null) {
notifyScreenshotError(mContext, mNotificationManager);
finisher.run();
return;
}
若截屏之后，截屏的bitmap對(duì)象為空，這里判斷截屏失敗，調(diào)用了notifyScreenshotError方法，發(fā)送截屏失敗的notification通知。
static void notifyScreenshotError(Context context, NotificationManager nManager) {
Resources r = context.getResources();
// Clear all existing notification, compose the new notification and show it
Notification.Builder b = new Notification.Builder(context)
.setTicker(r.getString(R.string.screenshot_failed_title))
.setContentTitle(r.getString(R.string.screenshot_failed_title))
.setContentText(r.getString(R.string.screenshot_failed_text))
.setSmallIcon(R.drawable.stat_notify_image_error)
.setWhen(System.currentTimeMillis())
.setVisibility(Notification.VISIBILITY_PUBLIC) // ok to show outside lockscreen
.setCategory(Notification.CATEGORY_ERROR)
.setAutoCancel(true)
.setColor(context.getColor(
com.android.internal.R.color.system_notification_accent_color));
Notification n =
new Notification.BigTextStyle(b)
.bigText(r.getString(R.string.screenshot_failed_text))
.build();
nManager.notify(R.id.notification_screenshot, n);
}
然后繼續(xù)看takeScreenshot方法，判斷截屏的圖像是否需要旋轉(zhuǎn)，若需要的話，則旋轉(zhuǎn)圖像：
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);
// Recycle the previous bitmap
mScreenBitmap.recycle();
mScreenBitmap = ss;
}
在takeScreenshot方法的最后若截屏成功，我們調(diào)用了：
// Start the post-screenshot animation
startAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,
statusBarVisible, navBarVisible);
開(kāi)始截屏的動(dòng)畫(huà)，好吧，看一下動(dòng)畫(huà)效果的實(shí)現(xiàn)：
/**
* Starts the animation after taking the screenshot
*/
private void startAnimation(final Runnable finisher, int w, int h, boolean statusBarVisible,
boolean navBarVisible) {
// Add the view for the animation
mScreenshotView.setImageBitmap(mScreenBitmap);
mScreenshotLayout.requestFocus();
// Setup the animation with the screenshot just taken
if (mScreenshotAnimation != null) {
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();
}
});
}
好吧，經(jīng)過(guò)著一些列的操作之后我們實(shí)現(xiàn)了截屏之后的動(dòng)畫(huà)效果了，這里暫時(shí)不分析動(dòng)畫(huà)效果，我們看一下動(dòng)畫(huà)效果之后做了哪些？還記不記的一般情況下我們截屏之后都會(huì)收到一個(gè)截屏的notification通知？這里應(yīng)該也是在其AnimatorListenerAdapter的onAnimationEnd方法中實(shí)現(xiàn)的，也就是動(dòng)畫(huà)執(zhí)行完成之后，我們看一下其saveScreenshotInWorkerThread方法的實(shí)現(xiàn)：
/**
* Creates a new worker thread and saves the screenshot to the media store.
*/
private void saveScreenshotInWorkerThread(Runnable finisher) {
SaveImageInBackgroundData data = new SaveImageInBackgroundData();
data.context = mContext;
data.image = mScreenBitmap;
data.iconSize = mNotificationIconSize;
data.finisher = finisher;
data.previewWidth = mPreviewWidth;
data.previewheight = mPreviewHeight;
if (mSaveInBgTask != null) {
mSaveInBgTask.cancel(false);
}
mSaveInBgTask = new SaveImageInBackgroundTask(mContext, data, mNotificationManager,
R.id.notification_screenshot).execute(data);
}
好吧，這里主要邏輯就是構(gòu)造了一個(gè)SaveImageInBackgroundTask對(duì)象，看樣子發(fā)送截屏成功的通知應(yīng)該是在這里實(shí)現(xiàn)的，我們看一下SaveImageInBackgroundTask構(gòu)造方法的實(shí)現(xiàn)邏輯：
SaveImageInBackgroundTask(Context context, SaveImageInBackgroundData data,
NotificationManager nManager, int nId) {
...
// Show the intermediate notification
mTickerAddSpace = !mTickerAddSpace;
mNotificationId = nId;
mNotificationManager = nManager;
final long now = System.currentTimeMillis();
mNotificationBuilder = new Notification.Builder(context)
.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)
.setColor(r.getColor(com.android.internal.R.color.system_notification_accent_color));
mNotificationStyle = new Notification.BigPictureStyle()
.bigPicture(picture.createAshmemBitmap());
mNotificationBuilder.setStyle(mNotificationStyle);
// For "public" situations we want to show all the same info but
// omit the actual screenshot image.
mPublicNotificationBuilder = new Notification.Builder(context)
.setContentTitle(r.getString(R.string.screenshot_saving_title))
.setContentText(r.getString(R.string.screenshot_saving_text))
.setSmallIcon(R.drawable.stat_notify_image)
.setCategory(Notification.CATEGORY_PROGRESS)
.setWhen(now)
.setColor(r.getColor(
com.android.internal.R.color.system_notification_accent_color));
mNotificationBuilder.setPublicVersion(mPublicNotificationBuilder.build());
Notification n = mNotificationBuilder.build();
n.flags |= Notification.FLAG_NO_CLEAR;
mNotificationManager.notify(nId, n);
// On the tablet, the large icon makes the notification appear as if it is clickable (and
// on small devices, the large icon is not shown) so defer showing the large icon until
// we compose the final post-save notification below.
mNotificationBuilder.setLargeIcon(icon.createAshmemBitmap());
// But we still don't set it for the expanded view, allowing the smallIcon to show here.
mNotificationStyle.bigLargeIcon((Bitmap) null);
}
可以發(fā)現(xiàn)在構(gòu)造方法的后面狗仔了一個(gè)NotificationBuilder對(duì)象，然后發(fā)送了一個(gè)截屏成功的Notification，這樣我們?cè)诮仄羷?dòng)畫(huà)之后就收到了Notification的通知了。
總結(jié)：
一般默認(rèn)情況下按下音量減少鍵和開(kāi)機(jī)鍵會(huì)執(zhí)行截圖動(dòng)作，程序執(zhí)行的入口就在在PhoneWindowManager的dispatchUnhandledKey方法中；然后通過(guò)TakeScreenshotService服務(wù)執(zhí)行截圖邏輯；通過(guò)nativie方法獲取截圖的bitmap，如果失敗調(diào)用失敗通知欄消息，如果成功調(diào)用截圖動(dòng)畫(huà)后發(fā)送成功通知欄消息。
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