最近遇到個新的需求，當電池溫度過高以及OVP狀態的時候，在使用者介面提示資訊。

電池電源資訊相關在Framework層/

與電池電量資訊等相關類：

1.BatteryManager.java

2.BatteryProperties.java

3.BatteryStates.java

4.PowerUI.java

5.LightService.java

6.PowerManager.java

7.BatteryService.java

這裡先分析BatteryService.java。

原始碼路徑： 

***/framework/base/services/java/com/android/server/BatteryService.java

BatteryService.java程式碼，必要的地方做了處理。

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.server;

import android.os.BatteryStats;
import com.android.internal.app.IBatteryStats;
import com.android.server.am.BatteryStatsService;

import android.app.ActivityManagerNative;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.BatteryManager;
import android.os.BatteryProperties;
import android.os.Binder;
import android.os.FileUtils;
import android.os.Handler;
import android.os.IBatteryPropertiesListener;
import android.os.IBatteryPropertiesRegistrar;
import android.os.IBinder;
import android.os.DropBoxManager;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.SystemClock;
import android.os.UEventObserver;
import android.os.UserHandle;
import android.provider.Settings;
import android.util.EventLog;
import android.util.Slog;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;


/**
 * <p>BatteryService monitors the charging status, and charge level of the device
 * battery.  When these values change this service broadcasts the new values
 * to all {@link android.content.BroadcastReceiver IntentReceivers} that are
 * watching the {@link android.content.Intent#ACTION_BATTERY_CHANGED
 * BATTERY_CHANGED} action.</p>
 * <p>The new values are stored in the Intent data and can be retrieved by
 * calling {@link android.content.Intent#getExtra Intent.getExtra} with the
 * following keys:</p>
 * <p>"scale" - int, the maximum value for the charge level</p>
 * <p>"level" - int, charge level, from 0 through "scale" inclusive</p>
 * <p>"status" - String, the current charging status.<br />
 * <p>"health" - String, the current battery health.<br />
 * <p>"present" - boolean, true if the battery is present<br />
 * <p>"icon-small" - int, suggested small icon to use for this state</p>
 * <p>"plugged" - int, 0 if the device is not plugged in; 1 if plugged
 * into an AC power adapter; 2 if plugged in via USB.</p>
 * <p>"voltage" - int, current battery voltage in millivolts</p>
 * <p>"temperature" - int, current battery temperature in tenths of
 * a degree Centigrade</p>
 * <p>"technology" - String, the type of battery installed, e.g. "Li-ion"</p>
 *
 * <p>
 * The battery service may be called by the power manager while holding its locks so
 * we take care to post all outcalls into the activity manager to a handler.
 *
 * FIXME: Ideally the power manager would perform all of its calls into the battery
 * service asynchronously itself.
 * </p>
 */
public final class BatteryService extends Binder {
    private static final String TAG = BatteryService.class.getSimpleName();

    private static final boolean DEBUG = false;

    //電量百分比顯示
    private static final int BATTERY_SCALE = 100;    // battery capacity is a percentage

    // Used locally for determining when to make a last ditch effort to log
    // discharge stats before the device dies.
    private int mCriticalBatteryLevel;

    private static final int DUMP_MAX_LENGTH = 24 * 1024;
    private static final String[] DUMPSYS_ARGS = new String[] { "--checkin", "--unplugged" };

    private static final String DUMPSYS_DATA_PATH = "/data/system/";

    // This should probably be exposed in the API, though it's not critical
    //沒有充電狀態則顯示0
    private static final int BATTERY_PLUGGED_NONE = 0;

    private final Context mContext;
    private final IBatteryStats mBatteryStats;
    private final Handler mHandler;

    private final Object mLock = new Object();

    private BatteryProperties mBatteryProps;
    private boolean mBatteryLevelCritical;
    private int mLastBatteryStatus;
    private int mLastBatteryHealth;
    private boolean mLastBatteryPresent;
    private int mLastBatteryLevel;
    private int mLastBatteryVoltage;
    private int mLastBatteryTemperature;
    private boolean mLastBatteryLevelCritical;

    private int mInvalidCharger;
    private int mLastInvalidCharger;

    private int mLowBatteryWarningLevel;
    private int mLowBatteryCloseWarningLevel;
    private int mShutdownBatteryTemperature;

    private int mPlugType;
    private int mLastPlugType = -1; // Extra state so we can detect first run

    private long mDischargeStartTime;
    private int mDischargeStartLevel;

    private boolean mUpdatesStopped;

    private Led mLed;

    private boolean mSentLowBatteryBroadcast = false;

    private BatteryListener mBatteryPropertiesListener;
    private IBatteryPropertiesRegistrar mBatteryPropertiesRegistrar;

    public BatteryService(Context context, LightsService lights) {
        mContext = context;
        mHandler = new Handler(true /*async*/);
        mLed = new Led(context, lights);
        mBatteryStats = BatteryStatsService.getService();

        mCriticalBatteryLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_criticalBatteryWarningLevel);
        //res/res/values/config.xml:547:    <integer name="config_lowBatteryWarningLevel">15</integer>
        mLowBatteryWarningLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryWarningLevel);
        //res/res/values/config.xml:550:    <integer name="config_lowBatteryCloseWarningLevel">20</integer> 接近警戒值。
        mLowBatteryCloseWarningLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryCloseWarningLevel);
        //res/res/values/config.xml:544:    <integer name="config_shutdownBatteryTemperature">680</integer>//68度？為什麼？
        mShutdownBatteryTemperature = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_shutdownBatteryTemperature);

        // watch for invalid charger messages if the invalid_charger switch exists
        if (new File("/sys/devices/virtual/switch/invalid_charger/state").exists()) {
            mInvalidChargerObserver.startObserving(
                    "DEVPATH=/devices/virtual/switch/invalid_charger");
        }

        //註冊監聽。實時更新電池電量資訊，底層傳遞上來的電池資訊有變化時，則上層會做響應的處理。
        //從這裡可以看出回撥介面中呼叫的update()方法應該是比較頻繁的。
        mBatteryPropertiesListener = new BatteryListener();

        IBinder b = ServiceManager.getService("batterypropreg");
        mBatteryPropertiesRegistrar = IBatteryPropertiesRegistrar.Stub.asInterface(b);

        try {
            mBatteryPropertiesRegistrar.registerListener(mBatteryPropertiesListener);
        } catch (RemoteException e) {
            // Should never happen.
        }
    }

    //該方法在SystemServer.java中呼叫。開機過程。
    void systemReady() {
        // check our power situation now that it is safe to display the shutdown dialog.
        synchronized (mLock) {
            shutdownIfNoPowerLocked();
            shutdownIfOverTempLocked();
        }
    }

    /**
     * Returns true if the device is plugged into any of the specified plug types.
     */
    public boolean isPowered(int plugTypeSet) {
        synchronized (mLock) {
            return isPoweredLocked(plugTypeSet);
        }
    }

    //當前手機是否正在充電。這裡面查查&的相關用法。
    private boolean isPoweredLocked(int plugTypeSet) {
        // assume we are powered if battery state is unknown so
        // the "stay on while plugged in" option will work.
        if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_UNKNOWN) {
            return true;
        }
        if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_AC) != 0 && mBatteryProps.chargerAcOnline) {
            return true;
        }
        if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_USB) != 0 && mBatteryProps.chargerUsbOnline) {
            return true;
        }
        if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_WIRELESS) != 0 && mBatteryProps.chargerWirelessOnline) {
            return true;
        }
        return false;
    }

    /**
     * Returns the current plug type.
     */
    public int getPlugType() {
        synchronized (mLock) {
            return mPlugType;
        }
    }

    /**
     * Returns battery level as a percentage.
     */
    public int getBatteryLevel() {
        synchronized (mLock) {
            return mBatteryProps.batteryLevel;
        }
    }

    /**
     * Returns true if battery level is below the first warning threshold.
     */
    public boolean isBatteryLow() {
        synchronized (mLock) {
            return mBatteryProps.batteryPresent && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel;
        }
    }

    /**
     * Returns a non-zero value if an  unsupported charger is attached.
     */
    public int getInvalidCharger() {
        synchronized (mLock) {
            return mInvalidCharger;
        }
    }

    private void shutdownIfNoPowerLocked() {
        // shut down gracefully if our battery is critically low and we are not powered.
        // wait until the system has booted before attempting to display the shutdown dialog.
        if (mBatteryProps.batteryLevel == 0 && !isPoweredLocked(BatteryManager.BATTERY_PLUGGED_ANY)) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (ActivityManagerNative.isSystemReady()) {
                        Intent intent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);
                        intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
                        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                    }
                }
            });
        }
    }

    private void shutdownIfOverTempLocked() {
        // shut down gracefully if temperature is too high (> 68.0C by default)
        // wait until the system has booted before attempting to display the
        // shutdown dialog.
        if (mBatteryProps.batteryTemperature > mShutdownBatteryTemperature) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (ActivityManagerNative.isSystemReady()) {
                        Intent intent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);
                        intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
                        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                    }
                }
            });
        }
    }

    private void update(BatteryProperties props) {
        synchronized (mLock) {
            if (!mUpdatesStopped) {
                //mBatteryProps即BatteryProperties，該類封裝了電量資訊的一些引數。實現了Parcelable介面。
                mBatteryProps = props;
                // Process the new values.
                processValuesLocked();
            }
        }
    }

    //這裡是處理電量等邏輯的主要位置。
    private void processValuesLocked() {
        boolean logOutlier = false;
        long dischargeDuration = 0;

        mBatteryLevelCritical = (mBatteryProps.batteryLevel <= mCriticalBatteryLevel);
        //當前的充電方式。AC,USB,WIRELESS(第三種有點高大上)
        if (mBatteryProps.chargerAcOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_AC;
        } else if (mBatteryProps.chargerUsbOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_USB;
        } else if (mBatteryProps.chargerWirelessOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;
        } else {
            mPlugType = BATTERY_PLUGGED_NONE;
        }
        
        //列印日誌，可以忽略。
        if (DEBUG) {
            Slog.d(TAG, "Processing new values: "
                    + "chargerAcOnline=" + mBatteryProps.chargerAcOnline
                    + ", chargerUsbOnline=" + mBatteryProps.chargerUsbOnline
                    + ", chargerWirelessOnline=" + mBatteryProps.chargerWirelessOnline
                    + ", batteryStatus=" + mBatteryProps.batteryStatus
                    + ", batteryHealth=" + mBatteryProps.batteryHealth
                    + ", batteryPresent=" + mBatteryProps.batteryPresent
                    + ", batteryLevel=" + mBatteryProps.batteryLevel
                    + ", batteryTechnology=" + mBatteryProps.batteryTechnology
                    + ", batteryVoltage=" + mBatteryProps.batteryVoltage
                    + ", batteryCurrentNow=" + mBatteryProps.batteryCurrentNow
                    + ", batteryChargeCounter=" + mBatteryProps.batteryChargeCounter
                    + ", batteryTemperature=" + mBatteryProps.batteryTemperature
                    + ", mBatteryLevelCritical=" + mBatteryLevelCritical
                    + ", mPlugType=" + mPlugType);
        }

        // Let the battery stats keep track of the current level.
        try {
            mBatteryStats.setBatteryState(mBatteryProps.batteryStatus, mBatteryProps.batteryHealth,
                    mPlugType, mBatteryProps.batteryLevel, mBatteryProps.batteryTemperature,
                    mBatteryProps.batteryVoltage);
        } catch (RemoteException e) {
            // Should never happen.
        }

        //電池電量耗盡以及溫度過高。
        shutdownIfNoPowerLocked();
        shutdownIfOverTempLocked();

        //mBatteryProps儲存之前的電量資訊，這裡做對比當資料資訊有變化的時候則表示電池狀態有變化。
        if (mBatteryProps.batteryStatus != mLastBatteryStatus ||
                mBatteryProps.batteryHealth != mLastBatteryHealth ||
                mBatteryProps.batteryPresent != mLastBatteryPresent ||
                mBatteryProps.batteryLevel != mLastBatteryLevel ||
                mPlugType != mLastPlugType ||
                mBatteryProps.batteryVoltage != mLastBatteryVoltage ||
                mBatteryProps.batteryTemperature != mLastBatteryTemperature ||
                mInvalidCharger != mLastInvalidCharger) {

            if (mPlugType != mLastPlugType) {
                //plugType前後變化，充電狀態--->非充電狀態，非充電狀態---->充電狀態
                if (mLastPlugType == BATTERY_PLUGGED_NONE) {
                    // discharging -> charging

                    // There's no value in this data unless we've discharged at least once and the
                    // battery level has changed; so don't log until it does.
                    if (mDischargeStartTime != 0 && mDischargeStartLevel != mBatteryProps.batteryLevel) {
                        dischargeDuration = SystemClock.elapsedRealtime() - mDischargeStartTime;
                        logOutlier = true;
                        EventLog.writeEvent(EventLogTags.BATTERY_DISCHARGE, dischargeDuration,
                                mDischargeStartLevel, mBatteryProps.batteryLevel);
                        // make sure we see a discharge event before logging again
                        mDischargeStartTime = 0;
                    }
                } else if (mPlugType == BATTERY_PLUGGED_NONE) {
                    // charging -> discharging or we just powered up
                    mDischargeStartTime = SystemClock.elapsedRealtime();
                    mDischargeStartLevel = mBatteryProps.batteryLevel;
                }
            }
            //列印Log,忽略++++++++++++++++++begin
            if (mBatteryProps.batteryStatus != mLastBatteryStatus ||
                    mBatteryProps.batteryHealth != mLastBatteryHealth ||
                    mBatteryProps.batteryPresent != mLastBatteryPresent ||
                    mPlugType != mLastPlugType) {
                EventLog.writeEvent(EventLogTags.BATTERY_STATUS,
                        mBatteryProps.batteryStatus, mBatteryProps.batteryHealth, mBatteryProps.batteryPresent ? 1 : 0,
                        mPlugType, mBatteryProps.batteryTechnology);
            }
            if (mBatteryProps.batteryLevel != mLastBatteryLevel) {
                // Don't do this just from voltage or temperature changes, that is
                // too noisy.
                EventLog.writeEvent(EventLogTags.BATTERY_LEVEL,
                        mBatteryProps.batteryLevel, mBatteryProps.batteryVoltage, mBatteryProps.batteryTemperature);
            }
            if (mBatteryLevelCritical && !mLastBatteryLevelCritical &&
                    mPlugType == BATTERY_PLUGGED_NONE) {
                // We want to make sure we log discharge cycle outliers
                // if the battery is about to die.
                dischargeDuration = SystemClock.elapsedRealtime() - mDischargeStartTime;
                logOutlier = true;
            }

            ///列印Log,忽略++++++++++++++++++end
            
            final boolean plugged = mPlugType != BATTERY_PLUGGED_NONE;//當前的充電狀態
            final boolean oldPlugged = mLastPlugType != BATTERY_PLUGGED_NONE;//上次的充電狀態

            //處理低電量狀態。傳送廣播，彈出AlertDialog，提示使用者電池電量低。
            /* The ACTION_BATTERY_LOW broadcast is sent in these situations:
             * - is just un-plugged (previously was plugged) and battery level is
             *   less than or equal to WARNING, or
             * - is not plugged and battery level falls to WARNING boundary
             *   (becomes <= mLowBatteryWarningLevel).
             */
            final boolean sendBatteryLow = !plugged//當前沒有充電
                    && mBatteryProps.batteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
                    && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel//當前電量小於警戒值
                    && (oldPlugged || mLastBatteryLevel > mLowBatteryWarningLevel);//上次在充或者上次的電量大於警戒值。

            //更新電池電量顯示
            sendIntentLocked();

            //++++++++++++++++power connected / not connected begin+++++++++++++++++++++++++++++++++++++++++++++
            //充電電源連線與充電電源拔出。
            // Separate broadcast is sent for power connected / not connected
            // since the standard intent will not wake any applications and some
            // applications may want to have smart behavior based on this.
            if (mPlugType != 0 && mLastPlugType == 0) {
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        //android4.4/framework/base/services/java/com/android/server/EntropyMixer.java:100
                        Intent statusIntent = new Intent(Intent.ACTION_POWER_CONNECTED);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }
            else if (mPlugType == 0 && mLastPlugType != 0) {
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        //麼有找到該廣播處理。
                        Intent statusIntent = new Intent(Intent.ACTION_POWER_DISCONNECTED);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }
            //++++++++++++++power connected / not connected end+++++++++++++++++++++++++++++++++++++++++++++++

            //當前是否處於低電量狀態
            //這兩個中ACTION_BATTERY_LOW和ACTION_BATTERY_OKAY沒有找到對應的處理，因此先忽略。這裡的ACTION_BATTERY_LOW
            //與低電量的顯示沒有多大關係.
            if (sendBatteryLow) {
                //當前處於低電量狀態，傳送該廣播
                mSentLowBatteryBroadcast = true;
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_BATTERY_LOW);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            } else if (mSentLowBatteryBroadcast && mLastBatteryLevel >= mLowBatteryCloseWarningLevel) {
                //當處於低電量時傳送ACTION_BATTERY_LOW廣播後，使用者插上了電源充電，此時，電池電量增加變化，如果變化到大於了20%，則會發送該廣播電池狀態正常OK狀態。
                mSentLowBatteryBroadcast = false;
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_BATTERY_OKAY);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }

            // Update the battery LED
            mLed.updateLightsLocked();

            // This needs to be done after sendIntent() so that we get the lastest battery stats.
            if (logOutlier && dischargeDuration != 0) {
                logOutlierLocked(dischargeDuration);
            }

            //當前的電量資訊更新完畢，儲存為最新狀態與下一次更新比較。
            mLastBatteryStatus = mBatteryProps.batteryStatus;
            mLastBatteryHealth = mBatteryProps.batteryHealth;
            mLastBatteryPresent = mBatteryProps.batteryPresent;
            mLastBatteryLevel = mBatteryProps.batteryLevel;
            mLastPlugType = mPlugType;
            mLastBatteryVoltage = mBatteryProps.batteryVoltage;
            mLastBatteryTemperature = mBatteryProps.batteryTemperature;
            mLastBatteryLevelCritical = mBatteryLevelCritical;
            mLastInvalidCharger = mInvalidCharger;
        }
    }

    //傳送廣播ACTION：ACTION_BATTERY_CHANGED，傳送當前電量資訊，更新UI顯示，該廣播的處理在SystemUI中的PowerUI.java中。
    private void sendIntentLocked() {
        //  Pack up the values and broadcast them to everyone
        final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                | Intent.FLAG_RECEIVER_REPLACE_PENDING);

        int icon = getIconLocked(mBatteryProps.batteryLevel);

        //將最新的電池電量資訊封裝到intent中，主動傳送給SystemUI,讓其顯示。
        intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryProps.batteryStatus);
        intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryProps.batteryHealth);
        intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryProps.batteryPresent);//這個表示啥意思？
        intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryProps.batteryLevel);
        intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
        intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
        intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
        intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryProps.batteryVoltage);
        intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryProps.batteryTemperature);
        intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryProps.batteryTechnology);
        intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);
        
        //日誌列印，可以忽略。
        if (DEBUG) {
            Slog.d(TAG, "Sending ACTION_BATTERY_CHANGED.  level:" + mBatteryProps.batteryLevel +
                    ", scale:" + BATTERY_SCALE + ", status:" + mBatteryProps.batteryStatus +
                    ", health:" + mBatteryProps.batteryHealth +  ", present:" + mBatteryProps.batteryPresent +
                    ", voltage: " + mBatteryProps.batteryVoltage +
                    ", temperature: " + mBatteryProps.batteryTemperature +
                    ", technology: " + mBatteryProps.batteryTechnology +
                    ", AC powered:" + mBatteryProps.chargerAcOnline + ", USB powered:" + mBatteryProps.chargerUsbOnline +
                    ", Wireless powered:" + mBatteryProps.chargerWirelessOnline +
                    ", icon:" + icon  + ", invalid charger:" + mInvalidCharger);
        }

        mHandler.post(new Runnable() {
            @Override
            public void run() {
                ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
            }
        });
    }

    private void logBatteryStatsLocked() {
        IBinder batteryInfoService = ServiceManager.getService(BatteryStats.SERVICE_NAME);
        if (batteryInfoService == null) return;

        DropBoxManager db = (DropBoxManager) mContext.getSystemService(Context.DROPBOX_SERVICE);
        if (db == null || !db.isTagEnabled("BATTERY_DISCHARGE_INFO")) return;

        File dumpFile = null;
        FileOutputStream dumpStream = null;
        try {
            // dump the service to a file
            dumpFile = new File(DUMPSYS_DATA_PATH + BatteryStats.SERVICE_NAME + ".dump");
            dumpStream = new FileOutputStream(dumpFile);
            batteryInfoService.dump(dumpStream.getFD(), DUMPSYS_ARGS);
            FileUtils.sync(dumpStream);

            // add dump file to drop box
            db.addFile("BATTERY_DISCHARGE_INFO", dumpFile, DropBoxManager.IS_TEXT);
        } catch (RemoteException e) {
            Slog.e(TAG, "failed to dump battery service", e);
        } catch (IOException e) {
            Slog.e(TAG, "failed to write dumpsys file", e);
        } finally {
            // make sure we clean up
            if (dumpStream != null) {
                try {
                    dumpStream.close();
                } catch (IOException e) {
                    Slog.e(TAG, "failed to close dumpsys output stream");
                }
            }
            if (dumpFile != null && !dumpFile.delete()) {
                Slog.e(TAG, "failed to delete temporary dumpsys file: "
                        + dumpFile.getAbsolutePath());
            }
        }
    }

    private void logOutlierLocked(long duration) {
        ContentResolver cr = mContext.getContentResolver();
        String dischargeThresholdString = Settings.Global.getString(cr,
                Settings.Global.BATTERY_DISCHARGE_THRESHOLD);
        String durationThresholdString = Settings.Global.getString(cr,
                Settings.Global.BATTERY_DISCHARGE_DURATION_THRESHOLD);

        if (dischargeThresholdString != null && durationThresholdString != null) {
            try {
                long durationThreshold = Long.parseLong(durationThresholdString);
                int dischargeThreshold = Integer.parseInt(dischargeThresholdString);
                if (duration <= durationThreshold &&
                        mDischargeStartLevel - mBatteryProps.batteryLevel >= dischargeThreshold) {
                    // If the discharge cycle is bad enough we want to know about it.
                    logBatteryStatsLocked();
                }
                if (DEBUG) Slog.v(TAG, "duration threshold: " + durationThreshold +
                        " discharge threshold: " + dischargeThreshold);
                if (DEBUG) Slog.v(TAG, "duration: " + duration + " discharge: " +
                        (mDischargeStartLevel - mBatteryProps.batteryLevel));
            } catch (NumberFormatException e) {
                Slog.e(TAG, "Invalid DischargeThresholds GService string: " +
                        durationThresholdString + " or " + dischargeThresholdString);
                return;
            }
        }
    }

    //獲取當前電池圖示顯示的drawableID
    //BATTERY_STATUS_DISCHARGING和BATTERY_STATUS_NOT_CHARGING應該差不多，因為從邏輯裡面看兩者狀態下都是用了相同的drawable資源。
    private int getIconLocked(int level) {
        if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_CHARGING) {//充電
            return com.android.internal.R.drawable.stat_sys_battery_charge;
        } else if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_DISCHARGING) {
            return com.android.internal.R.drawable.stat_sys_battery;
        } else if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_NOT_CHARGING
                || mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_FULL) {
            if (isPoweredLocked(BatteryManager.BATTERY_PLUGGED_ANY)
                    && mBatteryProps.batteryLevel >= 100) {
                return com.android.internal.R.drawable.stat_sys_battery_charge;
            } else {
                return com.android.internal.R.drawable.stat_sys_battery;
            }
        } else {
            return com.android.internal.R.drawable.stat_sys_battery_unknown;
        }
    }

    @Override
    protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.DUMP)
                != PackageManager.PERMISSION_GRANTED) {

            pw.println("Permission Denial: can't dump Battery service from from pid="
                    + Binder.getCallingPid()
                    + ", uid=" + Binder.getCallingUid());
            return;
        }

        synchronized (mLock) {
            if (args == null || args.length == 0 || "-a".equals(args[0])) {
                pw.println("Current Battery Service state:");
                if (mUpdatesStopped) {
                    pw.println("  (UPDATES STOPPED -- use 'reset' to restart)");
                }
                pw.println("  AC powered: " + mBatteryProps.chargerAcOnline);
                pw.println("  USB powered: " + mBatteryProps.chargerUsbOnline);
                pw.println("  Wireless powered: " + mBatteryProps.chargerWirelessOnline);
                pw.println("  status: " + mBatteryProps.batteryStatus);
                pw.println("  health: " + mBatteryProps.batteryHealth);
                pw.println("  present: " + mBatteryProps.batteryPresent);
                pw.println("  level: " + mBatteryProps.batteryLevel);
                pw.println("  scale: " + BATTERY_SCALE);
                pw.println("  voltage: " + mBatteryProps.batteryVoltage);

                if (mBatteryProps.batteryCurrentNow != Integer.MIN_VALUE) {
                    pw.println("  current now: " + mBatteryProps.batteryCurrentNow);
                }

                if (mBatteryProps.batteryChargeCounter != Integer.MIN_VALUE) {
                    pw.println("  charge counter: " + mBatteryProps.batteryChargeCounter);
                }

                pw.println("  temperature: " + mBatteryProps.batteryTemperature);
                pw.println("  technology: " + mBatteryProps.batteryTechnology);
            } else if (args.length == 3 && "set".equals(args[0])) {
                String key = args[1];
                String value = args[2];
                try {
                    boolean update = true;
                    if ("ac".equals(key)) {
                        mBatteryProps.chargerAcOnline = Integer.parseInt(value) != 0;
                    } else if ("usb".equals(key)) {
                        mBatteryProps.chargerUsbOnline = Integer.parseInt(value) != 0;
                    } else if ("wireless".equals(key)) {
                        mBatteryProps.chargerWirelessOnline = Integer.parseInt(value) != 0;
                    } else if ("status".equals(key)) {
                        mBatteryProps.batteryStatus = Integer.parseInt(value);
                    } else if ("level".equals(key)) {
                        mBatteryProps.batteryLevel = Integer.parseInt(value);
                    } else if ("invalid".equals(key)) {
                        mInvalidCharger = Integer.parseInt(value);
                    } else {
                        pw.println("Unknown set option: " + key);
                        update = false;
                    }
                    if (update) {
                        long ident = Binder.clearCallingIdentity();
                        try {
                            mUpdatesStopped = true;
                            processValuesLocked();
                        } finally {
                            Binder.restoreCallingIdentity(ident);
                        }
                    }
                } catch (NumberFormatException ex) {
                    pw.println("Bad value: " + value);
                }
            } else if (args.length == 1 && "reset".equals(args[0])) {
                long ident = Binder.clearCallingIdentity();
                try {
                    mUpdatesStopped = false;
                } finally {
                    Binder.restoreCallingIdentity(ident);
                }
            } else {
                pw.println("Dump current battery state, or:");
                pw.println("  set ac|usb|wireless|status|level|invalid <value>");
                pw.println("  reset");
            }
        }
    }

    private final UEventObserver mInvalidChargerObserver = new UEventObserver() {
        @Override
        public void onUEvent(UEventObserver.UEvent event) {
            final int invalidCharger = "1".equals(event.get("SWITCH_STATE")) ? 1 : 0;
            synchronized (mLock) {
                if (mInvalidCharger != invalidCharger) {
                    mInvalidCharger = invalidCharger;
                }
            }
        }
    };

    private final class Led {
        private final LightsService.Light mBatteryLight;

        private final int mBatteryLowARGB;
        private final int mBatteryMediumARGB;
        private final int mBatteryFullARGB;
        private final int mBatteryLedOn;
        private final int mBatteryLedOff;

        public Led(Context context, LightsService lights) {
            mBatteryLight = lights.getLight(LightsService.LIGHT_ID_BATTERY);

            //./core/res/res/values/config.xml:562:    <integer name="config_notificationsBatteryLowARGB">0xFFFF0000</integer>
            mBatteryLowARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLowARGB);
            //./core/res/res/values/config.xml:565:    <integer name="config_notificationsBatteryMediumARGB">0xFFFFFF00</integer>
            mBatteryMediumARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryMediumARGB);
            //./core/res/res/values/config.xml:568:    <integer name="config_notificationsBatteryFullARGB">0xFF00FF00</integer>
            mBatteryFullARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryFullARGB);
            //./core/res/res/values/config.xml:571:    <integer name="config_notificationsBatteryLedOn">125</integer>
            mBatteryLedOn = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLedOn);
            //./core/res/res/values/config.xml:577:    <integer name="config_notificationsBatteryLedOff">2875</integer>
            mBatteryLedOff = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLedOff);
        }

        /**
         * Synchronize on BatteryService.
         */
        public void updateLightsLocked() {
            final int level = mBatteryProps.batteryLevel;
            final int status = mBatteryProps.batteryStatus;
            if (level < mLowBatteryWarningLevel) { //當前電量處於低電量狀態
                if (status == BatteryManager.BATTERY_STATUS_CHARGING) {//處於低電量狀態，並且正在充電
                    // Solid red when battery is charging
                    mBatteryLight.setColor(mBatteryLowARGB);
                } else {//低電量狀態但是沒有充電
                    // Flash red when battery is low and not charging
                    mBatteryLight.setFlashing(mBatteryLowARGB, LightsService.LIGHT_FLASH_TIMED,
                            mBatteryLedOn, mBatteryLedOff);
                }
            } else if (status == BatteryManager.BATTERY_STATUS_CHARGING//當前屬於充電狀態
                    || status == BatteryManager.BATTERY_STATUS_FULL) {
                if (status == BatteryManager.BATTERY_STATUS_FULL || level >= 90) {
                    // Solid green when full or charging and nearly full
                    mBatteryLight.setColor(mBatteryFullARGB);
                } else {
                    // Solid orange when charging and halfway full
                    mBatteryLight.setColor(mBatteryMediumARGB);
                }
            } else {
                // No lights if not charging and not low
                mBatteryLight.turnOff();
            }
        }
    }

    private final class BatteryListener extends IBatteryPropertiesListener.Stub {
        public void batteryPropertiesChanged(BatteryProperties props) {
            BatteryService.this.update(props);
       }
    }
}
 

1.手機電量過低，彈出來的dialog資訊框是從哪裡實現的？

低電量時的廣播實際上就是BatteryService的sendIntentLocked() 方法中ACTION為ACTION_BATTERY_CHANGED的廣播，在SystemUI裡面接收引數判斷處理。

這個直接在PowerUI.java中檢視。從接收廣播，到解析資料，然後針對資料的各個情況做處理。

private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {
                //上一次電量
                final int oldBatteryLevel = mBatteryLevel;
                //最新電量
                mBatteryLevel = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 100);
                //上一次電池狀態
                final int oldBatteryStatus = mBatteryStatus;
                //最新電池狀態
                mBatteryStatus = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
                        BatteryManager.BATTERY_STATUS_UNKNOWN);
                //充電型別。AC,USB,WIRELESS
                final int oldPlugType = mPlugType;
                mPlugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 1);
                
                final int oldInvalidCharger = mInvalidCharger;
                mInvalidCharger = intent.getIntExtra(BatteryManager.EXTRA_INVALID_CHARGER, 0);

                //當前是否在充電
                final boolean plugged = mPlugType != 0;
                //上一次重新整理，是否在充電狀態。
                final boolean oldPlugged = oldPlugType != 0;

                //從方法來看，貌似就是電池的狀態是Ok的呢還是電量過低，
                int oldBucket = findBatteryLevelBucket(oldBatteryLevel);
                int bucket = findBatteryLevelBucket(mBatteryLevel);

                if (DEBUG) {
                    Slog.d(TAG, "buckets   ....." + mLowBatteryAlertCloseLevel
                            + " .. " + mLowBatteryReminderLevels[0]
                            + " .. " + mLowBatteryReminderLevels[1]);
                    Slog.d(TAG, "level          " + oldBatteryLevel + " --> " + mBatteryLevel);
                    Slog.d(TAG, "status         " + oldBatteryStatus + " --> " + mBatteryStatus);
                    Slog.d(TAG, "plugType       " + oldPlugType + " --> " + mPlugType);
                    Slog.d(TAG, "invalidCharger " + oldInvalidCharger + " --> " + mInvalidCharger);
                    Slog.d(TAG, "bucket         " + oldBucket + " --> " + bucket);
                    Slog.d(TAG, "plugged        " + oldPlugged + " --> " + plugged);
                }

                if (oldInvalidCharger == 0 && mInvalidCharger != 0) {
                    Slog.d(TAG, "showing invalid charger warning");
                    showInvalidChargerDialog();
                    return;
                } else if (oldInvalidCharger != 0 && mInvalidCharger == 0) {
                    dismissInvalidChargerDialog();
                } else if (mInvalidChargerDialog != null) {
                    // if invalid charger is showing, don't show low battery
                    return;
                }

                
                if (!plugged
                        && (bucket < oldBucket || oldPlugged)
                        && mBatteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
                        && bucket < 0) {
                    showLowBatteryWarning();

                    // only play SFX when the dialog comes up or the bucket changes
                    if (bucket != oldBucket || oldPlugged) {//可以體會到，當我們手機沒電了，恰好我們把充電拔了，就會有提示音。
                        playLowBatterySound();
                    }
                } else if (plugged || (bucket > oldBucket && bucket > 0)) {
                    //充電狀態
                    dismissLowBatteryWarning();
                } else if (mBatteryLevelTextView != null) {
                    //顯示低電量dialog
                    showLowBatteryWarning();
                }
            } else if (Intent.ACTION_SCREEN_OFF.equals(action)) {
                mScreenOffTime = SystemClock.elapsedRealtime();
            } else if (Intent.ACTION_SCREEN_ON.equals(action)) {
                mScreenOffTime = -1;
            } else {
                Slog.w(TAG, "unknown intent: " + intent);
            }
        }
    };
 

程式碼比較清晰，主要是電池資訊的一些情況判斷，需要多多琢磨一下為啥是這樣的。

//顯示低電量Dialog
    void showLowBatteryWarning() {
        Slog.i(TAG,
                ((mBatteryLevelTextView == null) ? "showing" : "updating")
                + " low battery warning: level=" + mBatteryLevel
                + " [" + findBatteryLevelBucket(mBatteryLevel) + "]");

        CharSequence levelText = mContext.getString(
                R.string.battery_low_percent_format, mBatteryLevel);

        //這裡的第一個if:因為電池的重新整理頻率比較高，因此如果此時dialog還在顯示狀態中，直接重新整理電量資訊即可。
        if (mBatteryLevelTextView != null) {
            mBatteryLevelTextView.setText(levelText);
        } else {
            View v = View.inflate(mContext, R.layout.battery_low, null);
            mBatteryLevelTextView = (TextView)v.findViewById(R.id.level_percent);

            mBatteryLevelTextView.setText(levelText);

            AlertDialog.Builder b = new AlertDialog.Builder(mContext);
                b.setCancelable(true);
                b.setTitle(R.string.battery_low_title);
                b.setView(v);
                b.setIconAttribute(android.R.attr.alertDialogIcon);
                b.setPositiveButton(android.R.string.ok, null);

            final Intent intent = new Intent(Intent.ACTION_POWER_USAGE_SUMMARY);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                    | Intent.FLAG_ACTIVITY_MULTIPLE_TASK
                    | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS
                    | Intent.FLAG_ACTIVITY_NO_HISTORY);
            if (intent.resolveActivity(mContext.getPackageManager()) != null) {
                b.setNegativeButton(R.string.battery_low_why,
                        new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                        dismissLowBatteryWarning();
                    }
                });
            }

            AlertDialog d = b.create();
            d.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    @Override
                    public void onDismiss(DialogInterface dialog) {
                        mLowBatteryDialog = null;
                        mBatteryLevelTextView = null;
                    }
                });
            //dialog屬性
            d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
            d.getWindow().getAttributes().privateFlags |=
                    WindowManager.LayoutParams.PRIVATE_FLAG_SHOW_FOR_ALL_USERS;
            d.show();
            mLowBatteryDialog = d;
        }
    }

2.拔掉充電器或者USB連線，狀態列的電池圖示是如何更新的？

當插拔資料線的時候，電池圖示的變化，是自定義View Draw出來的。具體在

packages/SystemUI/src/com/android/systemui/BatteryMeterView.java 。

3.低電量關機是如何實現的？

首先我們可以從BatteryService.java中看到有這麼個方法：

    private void shutdownIfNoPowerLocked() {
        // shut down gracefully if our battery is critically low and we are not powered.
        // wait until the system has booted before attempting to display the shutdown dialog.
        if (mBatteryProps.batteryLevel == 0 && !isPoweredLocked(BatteryManager.BATTERY_PLUGGED_ANY)) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (ActivityManagerNative.isSystemReady()) {
                        Intent intent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);
                        intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
                        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                    }
                }
            });
        }
    }

        <activity android:name="com.android.server.ShutdownActivity"
            android:permission="android.permission.SHUTDOWN"
            android:excludeFromRecents="true">
            <intent-filter>
                <action android:name="android.intent.action.ACTION_REQUEST_SHUTDOWN" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
            <intent-filter>
                <action android:name="android.intent.action.REBOOT" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

其中有人做了，但是涉及到一個許可權就是

android:permission="android.permission.SHUTDOWN"  

其中，android.excludeFromRecents="true" 表示當前開啟的Activity所屬應用，不會顯示在最近使用的列表裡。

/*
         * from BatteryService.java
         *Intent intent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);
         *intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
         *intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
         *mContext.startActivityAsUser(intent, UserHandle.CURRENT);
         *
         */
        Intent intent = getIntent();
        mReboot = Intent.ACTION_REBOOT.equals(intent.getAction());//from BatteryService傳遞過來的是Intent.ACTION_REQUEST_SHUTDOWN，這裡肯定是false。
        mConfirm = intent.getBooleanExtra(Intent.EXTRA_KEY_CONFIRM, false);
        Slog.i(TAG, "onCreate(): confirm=" + mConfirm);

        Thread thr = new Thread("ShutdownActivity") {
            @Override
            public void run() {
                IPowerManager pm = IPowerManager.Stub.asInterface(
                        ServiceManager.getService(Context.POWER_SERVICE));
                try {
                    //根據Action需求，是重啟還是關機。
                    if (mReboot) {
                        //接下來。。。。。
                        pm.reboot(mConfirm, null, false);
                    } else {
                        pm.shutdown(mConfirm, false);
                    }
                } catch (RemoteException e) {
                }
            }
        };
        thr.start();
        finish();
        // Wait for us to tell the power manager to shutdown.
        try {
     
            thr.join();
        } catch (InterruptedException e) {
        }
    }

8.app開發過程中，我們需要獲取電池電量資訊，如何來做？

當我們在開發app的時候需要獲取電池資訊，可以仿照BatteryService來做。 因為，BatteryService主動把電池電量資訊傳遞給了SystemUI. 

簡單的做法就是：

		getApplication().registerReceiver(new BroadcastReceiver() {
			
			@Override
			public void onReceive(Context context, Intent intent) {
				// TODO Auto-generated method stub
				//這裡的intent封裝了我們在BatterySerivce.java中sendIntentLocked()
				//封裝的電池電量資訊。
			}
		}, filter) ;

4.pm.reboot,pm.shutdown 的後續流程是如何實現的?

5.LED燈顯示 LightService

6.電池電量管理的底層研究。

7.BatteryService傳送廣播傳遞過程如何實現的。

比如這樣的

     Intent statusIntent = new Intent(Intent.ACTION_POWER_CONNECTED);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);

這裡就先原始碼跟蹤到這裡，下次繼續補充。