截屏事件流程

今天這篇文章我們主要講一下Android系統中的截屏事件處理流程。用過android系統手機的同學應該都知道,一般的android手機按下音量減少鍵和電源按鍵就會觸發截屏事件(國內定制機做個修改的這里就不做考慮了)。那么這里的截屏事件是如何觸發的呢?觸發之后android系統是如何實現截屏操作的呢?帶著這兩個問題,開始我們的源碼閱讀流程。

我們知道這里的截屏事件是通過我們的按鍵操作觸發的,所以這里就需要我們從android系統的按鍵觸發模塊開始看起,由于我們在不同的App頁面,操作音量減少鍵和電源鍵都會觸發系統的截屏處理,所以這里的按鍵觸發邏輯應該是Android系統的全局按鍵處理邏輯。

在android系統中,由于我們的每一個Android界面都是一個Activity,而界面的顯示都是通過Window對象實現的,每個Window對象實際上都是PhoneWindow的實例,而每個PhoneWindow對象都一個PhoneWindowManager對象,當我們在Activity界面執行按鍵操作的時候,在將按鍵的處理操作分發到App之前,首先會回調PhoneWindowManager中的dispatchUnhandledKey方法,該方法主要用于執行當前App處理按鍵之前的操作,我們具體看一下該方法的實現。

/** {@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;
    }

這里我們關注一下方法體中調用的:interceptFallback方法,通過調用該方法將處理按鍵的操作下發到該方法中,我們繼續看一下該方法的實現邏輯。

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方法中我們調用了interceptKeyBeforeQueueing方法,通過閱讀我們我們知道該方法主要實現了對截屏按鍵的處理流程,這樣我們繼續看一下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;
    }

可以發現這里首先判斷當前系統是否已經boot完畢,若尚未啟動完畢,則所有的按鍵操作都將失效,若啟動完成,則執行后續的操作,這里我們只是關注音量減少按鍵和電源按鍵組合的處理事件。另外這里多說一句想安卓系統的HOME按鍵事件,MENU按鍵事件,進程列表按鍵事件等等都是在這里實現的,后續中我們會陸續介紹這方面的內容。

回到我們的interceptKeyBeforeQueueing方法,當我用按下音量減少按鍵的時候回進入到:case KeyEvent.KEYCODE_VOLUME_MUTE分支并執行相應的邏輯,然后同時判斷用戶是否按下了電源鍵,若同時按下了電源鍵,則執行:

if (interactive && !mScreenshotChordVolumeDownKeyTriggered
                                && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
                            mScreenshotChordVolumeDownKeyTriggered = true;
                            mScreenshotChordVolumeDownKeyTime = event.getDownTime();
                            mScreenshotChordVolumeDownKeyConsumed = false;
                            cancelPendingPowerKeyAction();
                            interceptScreenshotChord();
                        }

可以發現這里的interceptScreenshotChrod方法就是系統準備開始執行截屏操作的開始,我們繼續看一下interceptcreenshotChord方法的實現。

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執行發送一個延遲的異步消息,請求執行截屏的操作而這里的延時時間,若當前輸入框是打開狀態,則延時時間為輸入框關閉時間加上系統配置的按鍵超時時間,若當前輸入框沒有打開則直接是系統配置的按鍵超時處理時間,可看一下getScreenshotChordLongPressDelay方法的具體實現。

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,發送了異步消息之后系統最終會被我們發送的Runnable對象的run方法執行,這里關于異步消息的邏輯可參考:android源碼解析之(二)-->異步消息機制

這樣我們看一下Runnable類型的mScreenshotRunnable的run方法的實現:

private final Runnable mScreenshotRunnable = new Runnable() {
        @Override
        public void run() {
            takeScreenshot();
        }
    };

好吧,方法體中并未執行其他操作,直接就是調用了takeScreenshot方法,這樣我們繼續看一下takeScreenshot方法的實現。

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);
            }
        }
    }

可以發現這里通過反射機制創建了一個TakeScreenshotService對象然后調用了bindServiceAsUser,這樣就創建了TakeScreenshotService服務并在服務創建之后發送了一個異步消息。好了,我們看一下TakeScreenshotService的實現邏輯。

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();
    }
}

可以發現在在TakeScreenshotService類的定義中有一個Handler成員變量,而我們在啟動TakeScreentshowService的時候回發送一個異步消息,這樣就會執行mHandler的handleMessage方法,然后在handleMessage方法中我們創建了一個GlobalScreenshow對象,然后執行了takeScreenshot方法,好吧,繼續看一下takeScreentshot方法的執行邏輯。

/**
     * 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參數:statusBarVisible,navBarVisible是否可見,而這兩個參數在我們PhoneWindowManager.takeScreenshot方法傳遞的:

if (mStatusBar != null && mStatusBar.isVisibleLw())
                            msg.arg1 = 1;
                        if (mNavigationBar != null && mNavigationBar.isVisibleLw())
                            msg.arg2 = 1;

可見若果mStatusBar可見,則傳遞的statusBarVisible為true,若mNavigationBar可見,則傳遞的navBarVisible為true。然后我們在截屏的時候判斷nStatusBar是否可見,mNavigationBar是否可見,若可見的時候則截屏同樣將其截屏出來。繼續回到我們的takeScreenshot方法,然后調用了:

// Take the screenshot
mScreenBitmap = SurfaceControl.screenshot((int) dims[0], (int) dims[1]);

方法,看注釋,這里就是執行截屏事件的具體操作了,然后我看一下SurfaceControl.screenshot方法的具體實現,另外這里需要注意的是,截屏之后返回的是一個Bitmap對象,其實熟悉android繪制機制的童鞋應該知道android中所有顯示能夠顯示的東西,在內存中表現都是Bitmap對象。

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,這里調用的是nativeScreenshot方法,它是一個native方法,具體的實現在JNI層,這里就不做過多的介紹了。繼續回到我們的takeScreenshot方法,在調用了截屏方法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對象為空,這里判斷截屏失敗,調用了notifyScreenshotError方法,發送截屏失敗的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);
    }

然后繼續看takeScreenshot方法,判斷截屏的圖像是否需要旋轉,若需要的話,則旋轉圖像:

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,我們調用了:

// Start the post-screenshot animation
        startAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,
                statusBarVisible, navBarVisible);

開始截屏的動畫,好吧,看一下動畫效果的實現:

/**
     * 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,經過著一些列的操作之后我們實現了截屏之后的動畫效果了,這里暫時不分析動畫效果,我們看一下動畫效果之后做了哪些?還記不記的一般情況下我們截屏之后都會收到一個截屏的notification通知?這里應該也是在其AnimatorListenerAdapter的onAnimationEnd方法中實現的,也就是動畫執行完成之后,我們看一下其saveScreenshotInWorkerThread方法的實現:

/**
     * 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造了一個SaveImageInBackgroundTask對象,看樣子發送截屏成功的通知應該是在這里實現的,我們看一下SaveImageInBackgroundTask構造方法的實現邏輯:

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);
    }

可以發現在構造方法的后面狗仔了一個NotificationBuilder對象,然后發送了一個截屏成功的Notification,這樣我們在截屏動畫之后就收到了Notification的通知了。

總結:

  • 在PhoneWindowManager的dispatchUnhandledKey方法中處理App無法處理的按鍵事件,當然也包括音量減少鍵和電源按鍵的組合按鍵

  • 通過一系列的調用啟動TakeScreenshotService服務,并通過其執行截屏的操作。

  • 具體的截屏代碼是在native層實現的。

  • 截屏操作時候,若截屏失敗則直接發送截屏失敗的notification通知。

  • 截屏之后,若截屏成功,則先執行截屏的動畫,并在動畫效果執行完畢之后,發送截屏成功的notification的通知。

另外對android源碼解析方法感興趣的可參考我的:
android源碼解析之(一)-->android項目構建過程
android源碼解析之(二)-->異步消息機制
android源碼解析之(三)-->異步任務AsyncTask
android源碼解析之(四)-->HandlerThread
android源碼解析之(五)-->IntentService
android源碼解析之(六)-->Log
android源碼解析之(七)-->LruCache
android源碼解析之(八)-->Zygote進程啟動流程
android源碼解析之(九)-->SystemServer進程啟動流程
android源碼解析之(十)-->Launcher啟動流程
android源碼解析之(十一)-->應用進程啟動流程
android源碼解析之(十二)-->系統啟動并解析Manifest的流程
android源碼解析之(十三)-->apk安裝流程
android源碼解析之(十四)-->Activity啟動流程
android源碼解析之(十五)-->Activity銷毀流程
android源碼解析(十六)-->應用進程Context創建流程
android源碼解析(十七)-->Activity布局加載流程
android源碼解析(十八)-->Activity布局繪制流程
android源碼解析(十九)-->Dialog加載繪制流程
android源碼解析(二十)-->Dialog取消繪制流程
android源碼解析(二十一)-->PopupWindow加載繪制流程
android源碼解析(二十二)-->Toast加載繪制流程
android源碼解析(二十三)-->Android異常處理流程
android源碼解析(二十四)-->onSaveInstanceState執行時機
android源碼解析(二十五)-->onLowMemory執行流程


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