首先找到开机键的响应事件frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager

 @Override
    public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
        if (!mSystemBooted) {

 case KeyEvent.KEYCODE_POWER: {
           

                EventLogTags.writeInterceptPower(
                        KeyEvent.actionToString(event.getAction()),
                        mPowerKeyHandled ? 1 : 0, mPowerKeyPressCounter);
                // Any activity on the power button stops the accessibility shortcut
                cancelPendingAccessibilityShortcutAction();
                result &= ~ACTION_PASS_TO_USER;
                isWakeKey = false; // wake-up will be handled separately
                if (down) {
                    interceptPowerKeyDown(event, interactive);
                } else {
                    interceptPowerKeyUp(event, interactive, canceled);
                }
                break;

进入方法interceptPowerKeyDown

    private void interceptPowerKeyDown(KeyEvent event, boolean interactive) {
        // Hold a wake lock until the power key is released.
        if (!mPowerKeyWakeLock.isHeld()) {
            mPowerKeyWakeLock.acquire();
        }

        // Cancel multi-press detection timeout.
        if (mPowerKeyPressCounter != 0) {
            mHandler.removeMessages(MSG_POWER_DELAYED_PRESS);
        }

        mWindowManagerFuncs.onPowerKeyDown(interactive);

        // Latch power key state to detect screenshot chord.
        if (interactive && !mScreenshotChordPowerKeyTriggered
                && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
            mScreenshotChordPowerKeyTriggered = true;
            mScreenshotChordPowerKeyTime = event.getDownTime();
            interceptScreenshotChord();
            interceptRingerToggleChord();
        }

进入方法interceptRingerToggleChord

private void interceptRingerToggleChord() {
    if (mRingerToggleChord != Settings.Secure.VOLUME_HUSH_OFF
            && mScreenshotChordPowerKeyTriggered && mA11yShortcutChordVolumeUpKeyTriggered) {
        final long now = SystemClock.uptimeMillis();
        if (now <= mA11yShortcutChordVolumeUpKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS
                && now <= mScreenshotChordPowerKeyTime
                + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) {
            mA11yShortcutChordVolumeUpKeyConsumed = true;
            cancelPendingPowerKeyAction();

            mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG_RINGER_TOGGLE_CHORD),
                    getRingerToggleChordDelay());
        }
    }
}

进入mHandler

 case MSG_RINGER_TOGGLE_CHORD:
                    handleRingerChordGesture();
                    break;

 private void handleRingerChordGesture() {
        if (mRingerToggleChord == VOLUME_HUSH_OFF) {
            return;
        }
        getAudioManagerInternal();
        mAudioManagerInternal.silenceRingerModeInternal("volume_hush");
        Settings.Secure.putInt(mContext.getContentResolver(), Settings.Secure.HUSH_GESTURE_USED, 1);
        mLogger.action(MetricsProto.MetricsEvent.ACTION_HUSH_GESTURE, mRingerToggleChord);
    }

进入方法AudioService文件frameworks/base/services/core/java/com/android/server/audio/AudioService

 public void silenceRingerModeInternal(String reason) {
        VibrationEffect effect = null;
        int ringerMode = AudioManager.RINGER_MODE_SILENT;
        int toastText = 0;

        int silenceRingerSetting = Settings.Secure.VOLUME_HUSH_OFF;
        if (mContext.getResources()
                .getBoolean(com.android.internal.R.bool.config_volumeHushGestureEnabled)) {
            silenceRingerSetting = Settings.Secure.getIntForUser(mContentResolver,
                    Settings.Secure.VOLUME_HUSH_GESTURE, VOLUME_HUSH_OFF,
                    UserHandle.USER_CURRENT);
        }

        switch(silenceRingerSetting) {
            case VOLUME_HUSH_MUTE:
                effect = VibrationEffect.get(VibrationEffect.EFFECT_DOUBLE_CLICK);
                ringerMode = AudioManager.RINGER_MODE_SILENT;
                toastText = com.android.internal.R.string.volume_dialog_ringer_guidance_silent;
                break;
            case VOLUME_HUSH_VIBRATE:
                effect = VibrationEffect.get(VibrationEffect.EFFECT_HEAVY_CLICK);
                ringerMode = AudioManager.RINGER_MODE_VIBRATE;
                toastText = com.android.internal.R.string.volume_dialog_ringer_guidance_vibrate;
                break;
        }
        maybeVibrate(effect, reason);
        setRingerModeInternal(ringerMode, reason);
        Toast.makeText(mContext, toastText, Toast.LENGTH_SHORT).show();
    }

这个方法里修改了变量ringerMode,在上篇随笔里讲了这个ringerMode