转载请标明出处：一片枫叶的专栏

前面我们讲解了系统截屏按键处理流程，HOME按键处理流程，今天再来讲解一下电源开关机按键事件流程，当然这也是系统按键处理流程方面的最后一篇博客了。 和截屏按键、HOME按键的处理流程类似，电源按键由于也是系统级别的按键，所以对其的事件处理逻辑是和截屏按键、HOME按键类似，不在某一个App中，而是在PhoneWindowManager的dispatchUnhandledKey方法中。所以和前面两篇类似，这里我们也是从PhoneWindowManager的dispatchUnhandledKey方法开始我们今天电源开关机按键的事件流程分析。 下面首先看一下dispatchUnhandledKey方法的实现逻辑： 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) { if (DEBUG_INPUT) { Slog.d(TAG, "Fallback: keyCode=" + fallbackAction.keyCode + " metaState=" + Integer.toHexString(fallbackAction.metaState)); } 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; } 通过前面两篇文章的分析
（ android源码解析（二十六）–>截屏事件流程  
android源码解析（二十七）–>HOME事件流程）
我们知道关于系统按键的处理逻辑被下放到了interceptFallback方法中，所以我们继续看一下interceptFallback方法的实现逻辑。 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; } 通过分析interceptFallback方法的源码，我们知道关于电源按键的处理逻辑在interceptKeyBeforeQueueing方法中，所以我们需要继续看一下interceptKeyBeforeQueueing方法中关于电源按键的处理逻辑。 public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) { ... case KeyEvent.KEYCODE_POWER: { result &= ~ACTION_PASS_TO_USER; isWakeKey = false; // wake-up will be handled separately if (down) { interceptPowerKeyDown(event, interactive); } else { interceptPowerKeyUp(event, interactive, canceled); } break; } ... return result; } 这里我们重点看一下电源按键的处理事件，可以发现当电源按键按下的时候我们调用了interceptPowerKeyDown方法，可以看出，这个方法就是处理电源事件的了，既然如此，我们继续看一下interceptPowerKeyDown方法的执行逻辑。 private void interceptPowerKeyDown(KeyEvent event, boolean interactive) { ... // Latch power key state to detect screenshot chord. if (interactive && !mScreenshotChordPowerKeyTriggered && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) { mScreenshotChordPowerKeyTriggered = true; mScreenshotChordPowerKeyTime = event.getDownTime(); interceptScreenshotChord(); } // Stop ringing or end call if configured to do so when power is pressed. TelecomManager telecomManager = getTelecommService(); boolean hungUp = false; if (telecomManager != null) { if (telecomManager.isRinging()) { // Pressing Power while there's a ringing incoming // call should silence the ringer. telecomManager.silenceRinger(); } else if ((mIncallPowerBehavior & Settings.Secure.INCALL_POWER_BUTTON_BEHAVIOR_HANGUP) != 0 && telecomManager.isInCall() && interactive) { // Otherwise, if "Power button ends call" is enabled, // the Power button will hang up any current active call. hungUp = telecomManager.endCall(); } } // If the power key has still not yet been handled, then detect short // press, long press, or multi press and decide what to do. mPowerKeyHandled = hungUp || mScreenshotChordVolumeDownKeyTriggered || mScreenshotChordVolumeUpKeyTriggered; if (!mPowerKeyHandled) { if (interactive) { // When interactive, we're already awake. // Wait for a long press or for the button to be released to decide what to do. if (hasLongPressOnPowerBehavior()) { Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS); msg.setAsynchronous(true); mHandler.sendMessageDelayed(msg, ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout()); } } else { wakeUpFromPowerKey(event.getDownTime()); if (mSupportLongPressPowerWhenNonInteractive && hasLongPressOnPowerBehavior()) { Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS); msg.setAsynchronous(true); mHandler.sendMessageDelayed(msg, ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout()); mBeganFromNonInteractive = true; } else { final int maxCount = getMaxMultiPressPowerCount(); if (maxCount <= 1) { mPowerKeyHandled = true; } else { mBeganFromNonInteractive = true; } } } } } 这里我们重点看一下if(interactive)分支，在这里我们发送一个一个异步消息，并且msg的what为MSG_POWER_LONG_PRESS，即长按电源事件的异步消息，所以我们看一下mHandler的handleMessage方法对该what消息的处理逻辑。 case MSG_POWER_LONG_PRESS: powerLongPress(); break; 我们可以发现在mHandler的handleMessage方法中当msg的what为MSG_POWER_LONG_PRESS时我们调用了powerLongPress方法，这个方法应该就是处理电源按键长按的逻辑，下面我们来看一下powerLongPress方法的实现。 private void powerLongPress() { final int behavior = getResolvedLongPressOnPowerBehavior(); switch (behavior) { case LONG_PRESS_POWER_NOTHING: break; case LONG_PRESS_POWER_GLOBAL_ACTIONS: mPowerKeyHandled = true; if (!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) { performAuditoryFeedbackForAccessibilityIfNeed(); } showGlobalActionsInternal(); break; case LONG_PRESS_POWER_SHUT_OFF: case LONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM: mPowerKeyHandled = true; performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false); sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS); mWindowManagerFuncs.shutdown(behavior == LONG_PRESS_POWER_SHUT_OFF); break; } } 可以发现这里有四个switch分之，其中第一个什么都不做直接break掉，第二个case则需要弹出选择操作界面，比如：飞行模式，开关机，静音模式，重新启动等，这里可以参看一下小米手机的关机界面：
然后第三第四个case分之则是直接调用关机方法，这里我们先看第二个case，看看系统是如何显示出关机操作界面的。那我们看一下showGlobalActionsInternal方法的实现逻辑。 void showGlobalActionsInternal() { sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS); if (mGlobalActions == null) { mGlobalActions = new GlobalActions(mContext, mWindowManagerFuncs); } final boolean keyguardShowing = isKeyguardShowingAndNotOccluded(); mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned()); if (keyguardShowing) { // since it took two seconds of long press to bring this up, // poke the wake lock so they have some time to see the dialog. mPowerManager.userActivity(SystemClock.uptimeMillis(), false); } } 可以发现我们首先调用了sendCloseSystemWindows方法，前面我们分析HOME按键流程的时候（android源码解析（二十七）–>HOME事件流程）知道该方法用于关机系统弹窗，比如输入法，壁纸等。然后我们创建了一个GlobalActions对象，并调用了其showDialog方法，通过分析源码，我们发现该方法就是用于显示长按电源按键弹出操作界面的，我们首先看一下GlobalActions的构造方法： public GlobalActions(Context context, WindowManagerFuncs windowManagerFuncs) { mContext = context; mWindowManagerFuncs = windowManagerFuncs; mAudioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE); mDreamManager = IDreamManager.Stub.asInterface( ServiceManager.getService(DreamService.DREAM_SERVICE)); // receive broadcasts IntentFilter filter = new IntentFilter(); filter.addAction(Intent.ACTION_CLOSE_SYSTEM_DIALOGS); filter.addAction(Intent.ACTION_SCREEN_OFF); filter.addAction(TelephonyIntents.ACTION_EMERGENCY_CALLBACK_MODE_CHANGED); context.registerReceiver(mBroadcastReceiver, filter); ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE); mHasTelephony = cm.isNetworkSupported(ConnectivityManager.TYPE_MOBILE); // get notified of phone state changes TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE); telephonyManager.listen(mPhoneStateListener, PhoneStateListener.LISTEN_SERVICE_STATE); mContext.getContentResolver().registerContentObserver( Settings.Global.getUriFor(Settings.Global.AIRPLANE_MODE_ON), true, mAirplaneModeObserver); Vibrator vibrator = (Vibrator) mContext.getSystemService(Context.VIBRATOR_SERVICE); mHasVibrator = vibrator != null && vibrator.hasVibrator(); mShowSilentToggle = SHOW_SILENT_TOGGLE && !mContext.getResources().getBoolean( com.android.internal.R.bool.config_useFixedVolume); } 可以看到在GlobalActions对象的构造方法中我们主要用于初始化其成员变量，由于我们的电源长按操作界面是一个全局页面，所以这里自定义了一个Window对象，下面我们看一下GlobalActions的showDialog方法。 public void showDialog(boolean keyguardShowing, boolean isDeviceProvisioned) { mKeyguardShowing = keyguardShowing; mDeviceProvisioned = isDeviceProvisioned; if (mDialog != null) { mDialog.dismiss(); mDialog = null; // Show delayed, so that the dismiss of the previous dialog completes mHandler.sendEmptyMessage(MESSAGE_SHOW); } else { handleShow(); } } 可以看到在showDialog方法中我们首先判断mDialog是否为空，若为空则发送msg的what为MESSAGE_SHOW的异步消息，否则调用handleShow方法，而这里的mDialog是一个类型为GlobalActionsDialog的变量，由于我们的mDialog为空，所以下面我们看一下handleShow方法。 private void handleShow() { awakenIfNecessary(); mDialog = createDialog(); prepareDialog(); // If we only have 1 item and it's a simple press action, just do this action. if (mAdapter.getCount() == 1 && mAdapter.getItem(0) instanceof SinglePressAction && !(mAdapter.getItem(0) instanceof LongPressAction)) { ((SinglePressAction) mAdapter.getItem(0)).onPress(); } else { WindowManager.LayoutParams attrs = mDialog.getWindow().getAttributes(); attrs.setTitle("GlobalActions"); mDialog.getWindow().setAttributes(attrs); mDialog.show(); mDialog.getWindow().getDecorView().setSystemUiVisibility(View.STATUS_BAR_DISABLE_EXPAND); } 在方法体中我们调用了createDialog方法，创建了GlobalActionsDialog类型的mDialog，这里我们看一下createDialog的实现方法。 private GlobalActionsDialog createDialog() { ... mAirplaneModeOn = new ToggleAction( R.drawable.ic_lock_airplane_mode, R.drawable.ic_lock_airplane_mode_off, R.string.global_actions_toggle_airplane_mode, R.string.global_actions_airplane_mode_on_status, R.string.global_actions_airplane_mode_off_status) { void onToggle(boolean on) { if (mHasTelephony && Boolean.parseBoolean( SystemProperties.get(TelephonyProperties.PROPERTY_INECM_MODE))) { mIsWaitingForEcmExit = true; // Launch ECM exit dialog Intent ecmDialogIntent = new Intent(TelephonyIntents.ACTION_SHOW_NOTICE_ECM_BLOCK_OTHERS, null); ecmDialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); mContext.startActivity(ecmDialogIntent); } else { changeAirplaneModeSystemSetting(on); } } @Override protected void changeStateFromPress(boolean buttonOn) { if (!mHasTelephony) return; // In ECM mode airplane state cannot be changed if (!(Boolean.parseBoolean( SystemProperties.get(TelephonyProperties.PROPERTY_INECM_MODE)))) { mState = buttonOn ? State.TurningOn : State.TurningOff; mAirplaneState = mState; } } public boolean showDuringKeyguard() { return true; } public boolean showBeforeProvisioning() { return false; } }; onAirplaneModeChanged(); mItems = new ArrayList(); String[] defaultActions = mContext.getResources().getStringArray( com.android.internal.R.array.config_globalActionsList); ArraySet addedKeys = new ArraySet(); for (int i = 0; i < defaultActions.length; i++) { String actionKey = defaultActions[i]; if (addedKeys.contains(actionKey)) { // If we already have added this, don't add it again. continue; } if (GLOBAL_ACTION_KEY_POWER.equals(actionKey)) { mItems.add(new PowerAction()); } else if (GLOBAL_ACTION_KEY_AIRPLANE.equals(actionKey)) { mItems.add(mAirplaneModeOn); } else if (GLOBAL_ACTION_KEY_BUGREPORT.equals(actionKey)) { if (Settings.Global.getInt(mContext.getContentResolver(), Settings.Global.BUGREPORT_IN_POWER_MENU, 0) != 0 && isCurrentUserOwner()) { mItems.add(getBugReportAction()); } } else if (GLOBAL_ACTION_KEY_SILENT.equals(actionKey)) { if (mShowSilentToggle) { mItems.add(mSilentModeAction); } } else if (GLOBAL_ACTION_KEY_USERS.equals(actionKey)) { if (SystemProperties.getBoolean("fw.power_user_switcher", false)) { addUsersToMenu(mItems); } } else if (GLOBAL_ACTION_KEY_SETTINGS.equals(actionKey)) { mItems.add(getSettingsAction()); } else if (GLOBAL_ACTION_KEY_LOCKDOWN.equals(actionKey)) { mItems.add(getLockdownAction()); } else if (GLOBAL_ACTION_KEY_VOICEASSIST.equals(actionKey)) { mItems.add(getVoiceAssistAction()); } else if (GLOBAL_ACTION_KEY_ASSIST.equals(actionKey)) { mItems.add(getAssistAction()); } else { Log.e(TAG, "Invalid global action key " + actionKey); } // Add here so we don't add more than one. addedKeys.add(actionKey); } mAdapter = new MyAdapter(); AlertParams params = new AlertParams(mContext); params.mAdapter = mAdapter; params.mOnClickListener = this; params.mForceInverseBackground = true; GlobalActionsDialog dialog = new GlobalActionsDialog(mContext, params); dialog.setCanceledOnTouchOutside(false); // Handled by the custom class. dialog.getListView().setItemsCanFocus(true); dialog.getListView().setLongClickable(true); dialog.getListView().setOnItemLongClickListener( new AdapterView.OnItemLongClickListener() { @Override public boolean onItemLongClick(AdapterView parent, View view, int position, long id) { final Action action = mAdapter.getItem(position); if (action instanceof LongPressAction) { return ((LongPressAction) action).onLongPress(); } return false; } }); dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG); dialog.setOnDismissListener(this); return dialog; } 方法体的内容比较长，我们看重点的内容，首先我们通过调用mContext.getResources().getStringArray(com.android.internal.R.array.config_globalActionsList)获得操作列表，这里可能包含：飞行模式、开关机、静音模式、重启等等，然后我们轮训操作列表，并添加相应的Action最后我们将这个操作列表保存到Dialog的adapter中并返回该dialog，然后我们回到我们刚刚的handleShow方法，在得到返回的dialog之后我们调用了dialog的show方法，这样我们就显示出了电源长按操作界面，比如小米的界面：
好吧，继续我们的分析，当我们长按电源按键弹出操作弹窗之后，这时候点击关机是怎么样的流程呢？我们发现在createDialog方法中关机操作adapter的item，我们添加了： mItems.add(new PowerAction()); 这样不难发现我们对关机按钮的操作封装在了PowerAction中，所以我们继续看一下PowerAction的实现。 private final class PowerAction extends SinglePressAction implements LongPressAction { private PowerAction() { super(com.android.internal.R.drawable.ic_lock_power_off, R.string.global_action_power_off); } @Override public boolean onLongPress() { UserManager um = (UserManager) mContext.getSystemService(Context.USER_SERVICE); if (!um.hasUserRestriction(UserManager.DISALLOW_SAFE_BOOT)) { mWindowManagerFuncs.rebootSafeMode(true); return true; } return false; } @Override public boolean showDuringKeyguard() { return true; } @Override public boolean showBeforeProvisioning() { return true; } @Override public void onPress() { // shutdown by making sure radio and power are handled accordingly. mWindowManagerFuncs.shutdown(false /* confirm */); } } 可以发现在PowerAction类的成员函数onPress方法中我们调用了mWindowManagerFuncs.showdown方法，而这个方法也就是开始执行我们的关机操作了，那么这里的mWindowManagerFuncs又是什么呢？它是在什么时候赋值的呢？通过分析我们发现这里的mWindowManagerFuncs成员变量是在GlobalActions的构造方法中赋值的。 public GlobalActions(Context context, WindowManagerFuncs windowManagerFuncs) { ... mWindowManagerFuncs = windowManagerFuncs; ... } 好吧，回到我们的PhoneWindowManager，早构造GlobalActions时，直接传递的是PhoneWindowManager的成员变量mWindowManagerFuncs，那么PhoneWindowManager的mWindowManagerFuncs成员变量又是何时被赋值的呢?通过分析源码我们能够看到PhoneWindowManager的mWindowManagerFuncs变量是在PhoneWindowManager的init方法中初始化的，好吧，再次查找PhoneWindowManager的init方法是何时被调用的。 经过查找终于在WindowManagerService中我们找到了PhoneWindowManager的init方法的调用。 private void initPolicy() { UiThread.getHandler().runWithScissors(new Runnable() { @Override public void run() { WindowManagerPolicyThread.set(Thread.currentThread(), Looper.myLooper()); mPolicy.init(mContext, WindowManagerService.this, WindowManagerService.this); } }, 0); } 这里的mPolicy就是一个PhoneWindowManager的实力，可以发现这里的init方法中mWindowManagerFuncs传递的就是一个WindowManagerService的实例，O(∩_∩)O哈哈~，让我们好找。 然么在PowerAction的onPress方法中调用的mWindowManagerFuncs.shutdown(false /* confirm */);方法，实际上调用的就是WindowManagerService的shutdown方法，这样我们继续看一下WindowManagerService的shutdown方法的实现。 @Override public void shutdown(boolean confirm) { ShutdownThread.shutdown(mContext, confirm); } 好吧，这里很简单就是直接调用了ShutdownThread的shutdown方法，看样子这里就是执行关机操作的封装了，继续看一下ShutdownThread的shutdown方法。 public static void shutdown(final Context context, boolean confirm) { mReboot = false; mRebootSafeMode = false; shutdownInner(context, confirm); } 可以看到在ShutdownThread的shutdown方法中代码很简单，具体的操作下发到了shutdownInner方法中，那么我们继续看一下shutdownInner方法的实现。 static void shutdownInner(final Context context, boolean confirm) { // ensure that only one thread is trying to power down. // any additional calls are just returned synchronized (sIsStartedGuard) { if (sIsStarted) { Log.d(TAG, "Request to shutdown already running, returning."); return; } } final int longPressBehavior = context.getResources().getInteger( com.android.internal.R.integer.config_longPressOnPowerBehavior); final int resourceId = mRebootSafeMode ? com.android.internal.R.string.reboot_safemode_confirm : (longPressBehavior == 2 ? com.android.internal.R.string.shutdown_confirm_question : com.android.internal.R.string.shutdown_confirm); Log.d(TAG, "Notifying thread to start shutdown longPressBehavior=" + longPressBehavior); if (confirm) { final CloseDialogReceiver closer = new CloseDialogReceiver(context); if (sConfirmDialog != null) { sConfirmDialog.dismiss(); } sConfirmDialog = new AlertDialog.Builder(context) .setTitle(mRebootSafeMode ? com.android.internal.R.string.reboot_safemode_title : com.android.internal.R.string.power_off) .setMessage(resourceId) .setPositiveButton(com.android.internal.R.string.yes, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int which) { beginShutdownSequence(context); } }) .setNegativeButton(com.android.internal.R.string.no, null) .create(); closer.dialog = sConfirmDialog; sConfirmDialog.setOnDismissListener(closer); sConfirmDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG); sConfirmDialog.show(); } else { beginShutdownSequence(context); } } 可以看到方法体中，首先判断若用户点击了关机按键是否弹出确认框，若弹出则弹出关机确认框，若不需要确认，则直接调用beginShutdownSequence方法，执行关机操作。而在关机确认框中我们的确认按钮也是执行了beginShutdownSequence方法，所以我们继续看一下关机方法beginShutdownSequence。 private static void beginShutdownSequence(Context context) { synchronized (sIsStartedGuard) { if (sIsStarted) { Log.d(TAG, "Shutdown sequence already running, returning."); return; } sIsStarted = true; } ... if (PowerManager.REBOOT_RECOVERY.equals(mRebootReason)) { mRebootUpdate = new File(UNCRYPT_PACKAGE_FILE).exists(); if (mRebootUpdate) { pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_update_title)); pd.setMessage(context.getText( com.android.internal.R.string.reboot_to_update_prepare)); pd.setMax(100); pd.setProgressNumberFormat(null); pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); pd.setProgress(0); pd.setIndeterminate(false); } else { // Factory reset path. Set the dialog message accordingly. pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_reset_title)); pd.setMessage(context.getText( com.android.internal.R.string.reboot_to_reset_message)); pd.setIndeterminate(true); } } else { pd.setTitle(context.getText(com.android.internal.R.string.power_off)); pd.setMessage(context.getText(com.android.internal.R.string.shutdown_progress)); pd.setIndeterminate(true); } pd.setCancelable(false); pd.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG); pd.show(); sInstance.mProgressDialog = pd; sInstance.mContext = context; sInstance.mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE); // make sure we never fall asleep again sInstance.mCpuWakeLock = null; try { sInstance.mCpuWakeLock = sInstance.mPowerManager.newWakeLock( PowerManager.PARTIAL_WAKE_LOCK, TAG + "-cpu"); sInstance.mCpuWakeLock.setReferenceCounted(false); sInstance.mCpuWakeLock.acquire(); } catch (SecurityException e) { Log.w(TAG, "No permission to acquire wake lock", e); sInstance.mCpuWakeLock = null; } // also make sure the screen stays on for better user experience sInstance.mScreenWakeLock = null; if (sInstance.mPowerManager.isScreenOn()) { try { sInstance.mScreenWakeLock = sInstance.mPowerManager.newWakeLock( PowerManager.FULL_WAKE_LOCK, TAG + "-screen"); sInstance.mScreenWakeLock.setReferenceCounted(false); sInstance.mScreenWakeLock.acquire(); } catch (SecurityException e) { Log.w(TAG, "No permission to acquire wake lock", e); sInstance.mScreenWakeLock = null; } } // start the thread that initiates shutdown sInstance.mHandler = new Handler() { }; sInstance.start(); } 在方法beginShutdownSequence中我们首先初始化了一个Process的dialog，该dialog用于显示关机界面，然后我们调用了sInstance.start方法，再往下的方法中就是真正的shutdown方法的实现，同时也是native方法，我们这里就不做过得解读了。。。 总结：

• 电源按键是系统按键，所以对电源按键的处理逻辑也是在PhoneWindowManager的dispatchUnhandledKey方法中；
• 在PhoneWindowManager的dispatchUnhandleKey方法处理Power按键之后会首先显示系统操作弹窗，一般包括但不限于：飞行模式，静音模式，重新启动，关机等；
• 当用户点击关机按钮是调用的是WindowManagerService.shutdown方法，而内部调用的是ShutdownThread.shutdown方法；

另外对android源码解析方法感兴趣的可参考我的：
android源码解析之（一）–>android项目构建过程
android源码解析之（二）–>异步消息机制
android源码解析之（三）–>异步任务AsyncTask
android源码解析之（四）–>HandlerThread
android源码解析之（五）–>IntentService
android源码解析之（六）–>Log
android源码解析之（七）–>LruCache
android源码解析之（八）–>Zygote进程启动流程
android源码解析之（九）–>SystemServer进程启动流程
android源码解析之（十）–>Launcher启动流程
android源码解析之（十一）–>应用进程启动流程
android源码解析之（十二）–>系统启动并解析Manifest的流程
android源码解析之（十三）–>apk安装流程
android源码解析之（十四）–>Activity启动流程
android源码解析之（十五）–>Activity销毁流程
android源码解析（十六）–>应用进程Context创建流程
android源码解析（十七）–>Activity布局加载流程
android源码解析（十八）–>Activity布局绘制流程
android源码解析（十九）–>Dialog加载绘制流程
android源码解析（二十）–>Dialog取消绘制流程
android源码解析（二十一）–>PopupWindow加载绘制流程
android源码解析（二十二）–>Toast加载绘制流程
android源码解析（二十三）–>Android异常处理流程
android源码解析（二十四）–>onSaveInstanceState执行时机
android源码解析（二十五）–>onLowMemory执行流程
android源码解析（二十六）–>截屏事件流程
android源码解析（二十七）–>HOME事件流程

---

本文以同步至github中：https://github.com/yipianfengye/androidSource，欢迎star和follow

---