按键的处理主要由InputManagerService负责，属于Android输入系统的流程。在这篇博客里，我们只关注与Power键相关的内容。InputManagerService处理的按键事件，最终将会传递到PhoneWindowManager的interceptKeyBeforeQueueing函数。
我们就从这个函数开始，逐步进行分析。
public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
if (!mSystemBooted) {
// If we have not yet booted, don't let key events do anything.
return 0;
}
//表示屏幕是否点亮
final boolean interactive = (policyFlags & FLAG_INTERACTIVE) != 0;
final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
final boolean canceled = event.isCanceled();
//按键对应的编码
final int keyCode = event.getKeyCode();
.................
switch (keyCode) {
...........
case KeyEvent.KEYCODE_POWER: {
result &= ~ACTION_PASS_TO_USER;
isWakeKey = false; // wake-up will be handled separately
if (down) {
//处理按下Power键
interceptPowerKeyDown(event, interactive);
} else {
//处理松开Power键
interceptPowerKeyUp(event, interactive, canceled);
}
break;
}
}
..............
if (isWakeKey) {
//按power键时，isWakeKey置为false，于是不会调用wakeUp函数
wakeUp(event.getEventTime(), mAllowTheaterModeWakeFromKey, "android.policy:KEY");
}
return result;
}接下来，我们分别看一下interceptPowerKeyDown和interceptPowerKeyUp函数。
一、interceptPowerKeyDown
interceptPowerKeyDown用于处理按下Power键(还未松手释放)对应的事件。
private void interceptPowerKeyDown(KeyEvent event, boolean interactive) {
// Hold a wake lock until the power key is released.
// mPowerKeyWakeLock为PARTIAL_WAKE_LOCK级别的锁
if (!mPowerKeyWakeLock.isHeld()) {
//将调用到PMS的acquire WakeLock流程
mPowerKeyWakeLock.acquire();
}
// Cancel multi-press detection timeout.
//处理多次按power键的场景
//每次power up时，发送MSG_POWER_DELAYED_PRESS的延迟消息
//如果延迟消息被处理，说明一次完整的Power键处理结束（按下去，弹起来）
//在延迟消息被处理前，再次按power键，就检测到多次点击了
//实际上，原生终端不支持该场景
if (mPowerKeyPressCounter != 0) {
mHandler.removeMessages(MSG_POWER_DELAYED_PRESS);
}
// Detect user pressing the power button in panic when an application has
// taken over the whole screen.
// 从注释来看及mHiddenNavPanic的代码，觉得像是处理“误触”的
boolean panic = mImmersiveModeConfirmation.onPowerKeyDown(interactive,
SystemClock.elapsedRealtime(), isImmersiveMode(mLastSystemUiFlags));
if (panic) {
mHandler.post(mHiddenNavPanic);
}
// Latch power key state to detect screenshot chord.
// 如果当前是亮屏状态，且满足触发截屏的条件，触发截屏功能
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.
//如果有电话拨入，且电话铃声响起，按Power键，设置电话响铃静音
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.
//如果正在接听电话，且配置了Power键挂断电话的话，按Power按键挂断正在接听的电话
hungUp = telecomManager.endCall();
}
}
GestureLauncherService gestureService = LocalServices.getService(
GestureLauncherService.class);
boolean gesturedServiceIntercepted = false;
if (gestureService != null) {
//手势对应的服务，尝试拦截处理Power键动作事件
gesturedServiceIntercepted = gestureService.interceptPowerKeyDown(event, interactive,
mTmpBoolean);
if (mTmpBoolean.value && mGoingToSleep) {
mCameraGestureTriggeredDuringGoingToSleep = true;
}
}
// If the power key has still not yet been handled, then detect short
// press, long press, or multi press and decide what to do.
// Power键事件的处理，就像处理屏幕上的点击事件一样，也依赖于事件分发机制
// 如果已经被消耗掉了，就不会再被继续处理
mPowerKeyHandled = hungUp || mScreenshotChordVolumeDownKeyTriggered
|| mScreenshotChordVolumeUpKeyTriggered || gesturedServiceIntercepted;
//Power键事件未被消耗掉
if (!mPowerKeyHandled) {
//屏幕还是亮的
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.
//1、 判断是否支持长按的行为
if (hasLongPressOnPowerBehavior()) {
//2、 亮屏时，长按Power键将触发MSG_POWER_LONG_PRESS消息
Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
msg.setAsynchronous(true);
mHandler.sendMessageDelayed(msg,
ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
}
} else {
//此时屏幕是熄灭状态
//3、先唤醒系统，这个会调用到PMS的wakeUp
wakeUpFromPowerKey(event.getDownTime());
//支持熄屏长按，mSupportLongPressPowerWhenNonInteractive读资源文件得到，默认为false
if (mSupportLongPressPowerWhenNonInteractive && hasLongPressOnPowerBehavior()) {
Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
msg.setAsynchronous(true);
mHandler.sendMessageDelayed(msg,
ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
mBeganFromNonInteractive = true;
} else {
//默认返回1
final int maxCount = getMaxMultiPressPowerCount();
if (maxCount <= 1) {
//息屏时，按下power键（不弹起），仅消耗掉该事件
mPowerKeyHandled = true;
} else {
mBeganFromNonInteractive = true;
}
}
}
}
}1、hasLongPressOnPowerBehavior
hasLongPressOnPowerBehavior负责判断终端是否支持长按的行为：
private boolean hasLongPressOnPowerBehavior() {
return getResolvedLongPressOnPowerBehavior() != LONG_PRESS_POWER_NOTHING;
}
private int getResolvedLongPressOnPowerBehavior() {
//取决与系统属性"factory.long_press_power_off"，此处默认为false
if (FactoryTest.isLongPressOnPowerOffEnabled()) {
return LONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM;
}
return mLongPressOnPowerBehavior;
}从上面的代码可以看出，终端是否支持长按行为，最终将由mLongPressOnPowerBehavior决定。
.........
mLongPressOnPowerBehavior = mContext.getResources().getInteger(
com.android.internal.R.integer.config_longPressOnPowerBehavior);
.........mLongPressOnPowerBehavior将在PhoneWindowManager初始化时，通过读取资源文件得到，一般情况下应该为1。
于是，hasLongPressOnPowerBehavior的值返回true，即终端支持Power键长按。
2、MSG_POWER_LONG_PRESS的处理
从上面的代码，我们知道亮屏时按Power键，会触发延迟的MSG_POWER_LONG_PRESS消息。
如果在MSG_POWER_LONG_PRESS超时前，Power键未被释放掉，那么此次操作被定义为长按Power键。
MSG_POWER_LONG_PRESS对应的处理函数为powerLongPress：
private void powerLongPress() {
//也是由资源文件得到，默认为1，即LONG_PRESS_POWER_GLOBAL_ACTIONS
final int behavior = getResolvedLongPressOnPowerBehavior();
switch (behavior) {
case LONG_PRESS_POWER_NOTHING:
break;
case LONG_PRESS_POWER_GLOBAL_ACTIONS:
mPowerKeyHandled = true;
//感觉这里是：终端对接收的事件处理后，给用户一个反馈信息
//performHapticFeedbackLw主要进行震动反馈，例如按键后，终端震动一下
//不同的事件，定义了不同的震动模式
if (!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) {
//如果没有震动反馈，这里尝试进行声音的反馈，例如响一下按键音
performAuditoryFeedbackForAccessibilityIfNeed();
}
//弹出选择关机还是重启的对话框
showGlobalActionsInternal();
break;
.........
}
}3、wakeUpFromPowerKey
在息屏的状态下按下Power键，将调用wakeUpFromPowerKey函数唤醒系统：
private void wakeUpFromPowerKey(long eventTime) {
//从config.xml来看，mAllowTheaterModeWakeFromPowerKey默认为true
wakeUp(eventTime, mAllowTheaterModeWakeFromPowerKey, "android.policy:POWER");
}
private boolean wakeUp(long wakeTime, boolean wakeInTheaterMode, String reason) {
//取数据库的值
final boolean theaterModeEnabled = isTheaterModeEnabled();
//按Power键时，条件返回false
if (!wakeInTheaterMode && theaterModeEnabled) {
return false;
}
//看来唤醒时，将退出剧院模式
if (theaterModeEnabled) {
Settings.Global.putInt(mContext.getContentResolver(),
Settings.Global.THEATER_MODE_ON, 0);
}
//最终将调用到PMS的wakeUp函数
mPowerManager.wakeUp(wakeTime, reason);
return true;
}我们跟进一下PMS的wakeUp函数：
public void wakeUp(long eventTime, String reason, String opPackageName) {
..........
try {
wakeUpInternal(eventTime, reason, uid, opPackageName, uid);
} finally {
...............
}
}
private void wakeUpInternal(long eventTime, String reason, int uid, String opPackageName,
int opUid) {
synchronized (mLock) {
//更新Wakefullness的状态为WAKEFULNESS_AWAKE，记录一次UserActivity
if (wakeUpNoUpdateLocked(eventTime, reason, uid, opPackageName, opUid)) {
//如之前博客所述，对整个电源状态进行一次调整，将在需要时点亮屏幕
updatePowerStateLocked();
}
}
}二、interceptPowerKeyUp
interceptPowerKeyUp处理松开Power键后的流程：
private void interceptPowerKeyUp(KeyEvent event, boolean interactive, boolean canceled) {
//事件被取消，或者在按下Power键时，该事件已被消耗掉
//那么就不用继续处理
final boolean handled = canceled || mPowerKeyHandled;
mScreenshotChordPowerKeyTriggered = false;
//退出截屏
cancelPendingScreenshotChordAction();
//取消MSG_POWER_LONG_PRESS事件，即在一定事件内Power键弹起，则表示这一次不是长按Power键
cancelPendingPowerKeyAction();
//从之前的代码，我们知道除了特殊功能外
//灭屏按Power键或亮屏长按时，均会消耗掉Power事件
//因此，只有亮屏短按Power键需要进行处理
if (!handled) {
// Figure out how to handle the key now that it has been released.
// 记录短按的次数
mPowerKeyPressCounter += 1;
final int maxCount = getMaxMultiPressPowerCount();
final long eventTime = event.getDownTime();
if (mPowerKeyPressCounter < maxCount) {
// This could be a multi-press. Wait a little bit longer to confirm.
// Continue holding the wake lock.
// 与之前interceptPowerKeyDown，处理Power键被多次按下场景对应
// 每次被按下，均发送MSG_POWER_DELAYED_PRESS消息
// 实际上maxCount为1，该不会进入该分支
Message msg = mHandler.obtainMessage(MSG_POWER_DELAYED_PRESS,
interactive ? 1 : 0, mPowerKeyPressCounter, eventTime);
msg.setAsynchronous(true);
mHandler.sendMessageDelayed(msg, ViewConfiguration.getDoubleTapTimeout());
return;
}
//1、No other actions. Handle it immediately.
powerPress(eventTime, interactive, mPowerKeyPressCounter);
}
// 2、Done. Reset our state.
finishPowerKeyPress();
}1、powerPress
我们跟进一下powerPress函数：
private void powerPress(long eventTime, boolean interactive, int count) {
if (mScreenOnEarly && !mScreenOnFully) {
Slog.i(TAG, "Suppressed redundant power key press while "
+ "already in the process of turning the screen on.");
return;
}
if (count == 2) {
//原生不进入
powerMultiPressAction(eventTime, interactive, mDoublePressOnPowerBehavior);
} else if (count == 3) {
//原生不进入
powerMultiPressAction(eventTime, interactive, mTriplePressOnPowerBehavior);
} else if (interactive && !mBeganFromNonInteractive) {
//亮屏时，将进入该分支
//mShortPressOnPowerBehavior被配置为1
switch (mShortPressOnPowerBehavior) {
case SHORT_PRESS_POWER_NOTHING:
break;
case SHORT_PRESS_POWER_GO_TO_SLEEP:
//最终调用到PMS的goToSleep函数
mPowerManager.goToSleep(eventTime,
PowerManager.GO_TO_SLEEP_REASON_POWER_BUTTON, 0);
break;
...............
}
}
}从上面的代码可以看出，在亮屏状态下，短按一下Power键，最终将调用到PMS的goToSleep函数，使终端进入到休眠状态，与实际情况一致。
我们跟进一下PMS的goToSleep函数：
public void goToSleep(long eventTime, int reason, int flags) {
............
try {
goToSleepInternal(eventTime, reason, flags, uid);
} finally {
...............
}
}
private void goToSleepInternal(long eventTime, int reason, int flags, int uid) {
synchronized (mLock) {
//没有触发用户事件，将mWakefullness置为WAKEFULNESS_DOZING
if (goToSleepNoUpdateLocked(eventTime, reason, flags, uid)) {
//执行整体的电源状态更新，将熄灭屏幕
updatePowerStateLocked();
}
}2、finishPowerKeyPress
每当处理一次完整的Power键按下、弹出操作后，interceptPowerKeyUp调用finishPowerKeyPress进行最后的状态复位操作：
private void finishPowerKeyPress() {
mBeganFromNonInteractive = false;
mPowerKeyPressCounter = 0;
if (mPowerKeyWakeLock.isHeld()) {
mPowerKeyWakeLock.release();
}
}从代码可以看出，主要的工作其实就是将状态变量恢复为初始值，同时释放掉最初申请的锁。
三、总结
整个Power按键的主要处理流程如上图所示。结合手机的实际情况，整个逻辑还是非常好理解的。