1. 剩余可用时长 BatteryStatsImpl.computeBatteryTimeRemaining 函数

http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/com/android/internal/os/BatteryStatsImpl.java

**公式：剩余电池可用时长 = 每消耗1%的电量的平均时间 * 当前电量值 **

原理：统计出每次放电的电量变化的时间，获得每消耗1%的电量的平均时间，再根据当前电量值，从而得到预计可以时长

    @Override    public long computeBatteryTimeRemaining(long curTime) {        // 当前为充电状态，则无剩余可用时长        if (!mOnBattery) {            return -1;        }        // 无放电电池信息，则无剩余可用时长        if (mDischargeStepTracker.mNumStepDurations < 1) {            return -1;        }        // 无每消耗1%的电量的平均时间，则无剩余可用时长        long msPerLevel = mDischargeStepTracker.computeTimePerLevel();        if (msPerLevel <= 0) {            return -1;        }        // 剩余电池可用时长 = 每消耗1%的电量的平均时间 * 当前电量值         return (msPerLevel * mCurrentBatteryLevel) * 1000;    }

1.1 是否充电状态 - mOnBattery

    boolean mOnBattery;        // This should probably be exposed in the API, though it's not critical    public static final int BATTERY_PLUGGED_NONE = OsProtoEnums.BATTERY_PLUGGED_NONE; // = 0        // Plug states, primarily used by android/os/BatteryManager.java.    enum BatteryPluggedStateEnum {        // Note that NONE is not in BatteryManager.java's constants.        BATTERY_PLUGGED_NONE = 0;        // Power source is an AC charger.        BATTERY_PLUGGED_AC = 1;        // Power source is a USB port.        BATTERY_PLUGGED_USB = 2;        // Power source is wireless.        BATTERY_PLUGGED_WIRELESS = 4;    }        public static boolean isOnBattery(int plugType, int status) {        // 当前未充电 && 当前电池状态不为未知状态        return plugType == BATTERY_PLUGGED_NONE && status != BatteryManager.BATTERY_STATUS_UNKNOWN;    }        @GuardedBy("this")    public void setBatteryStateLocked(final int status, final int health, final int plugType,            final int level, /* not final */ int temp, final int volt, final int chargeUAh,            final int chargeFullUAh) {        final boolean onBattery = isOnBattery(plugType, status);        ...        setOnBatteryLocked(elapsedRealtime, uptime, onBattery, oldStatus, level, chargeUAh);        ...    }        @GuardedBy("this")    protected void setOnBatteryLocked(final long mSecRealtime, final long mSecUptime,            final boolean onBattery, final int oldStatus, final int level, final int chargeUAh) {        ...        if (onBattery) {            mOnBattery = mOnBatteryInternal = true;        } else {            mOnBattery = mOnBatteryInternal = false;        }        ...    }

1.2 放电电池信息条数 mDischargeStepTracker.mNumStepDurations

查看 batterystats-daily.xml 电池信息条数，例如记录不同时间的灭屏、亮屏、省电模式、idle模式、充放电等信息

    // 读取每日电池信息    public void readDailyStatsLocked() {        ...        // 电池每日使用信息        // 路径: /data/system/batterystats-daily.xml                // 0x 00          00           00    ffffffffff        // 0x 00[modMode] 00[initMode] level 时间（duration）        // initMode和modMode 中:        // 00(灭屏 f) 01(亮屏 o) 02(doze d) 03(doze supend z)        // 04(省电模式 p) 08(idle模式 i)        mDailyFile = new AtomicFile(new File(systemDir, "batterystats-daily.xml"));        stream = mDailyFile.openRead();        parser.setInput(stream, StandardCharsets.UTF_8.name());        ...        readDailyItemsLocked(parser);        ...    }    void readDailyItemTagDetailsLocked(XmlPullParser parser, DailyItem dit, boolean isCharge,            String tag)            throws NumberFormatException, XmlPullParserException, IOException {        ...            if ("s".equals(tagName)) {                if (i < num) {                    String valueAttr = parser.getAttributeValue(null, "v");                    if (valueAttr != null) {                        // 例如 0x020362ffffffff00L:zD-62-ffffffff00                        // 表示当前为doze supend,上一次为 doze，电量为 0x62, 时间为ffffffff00                        steps.decodeEntryAt(i, valueAttr);                        i++;                    }                }            }        ...        // 每日电池信息        steps.mNumStepDurations = i;        ...    }

1.3 每消耗1%的电量的平均时间 mDischargeStepTracker.computeTimePerLevel()

    public static final long STEP_LEVEL_TIME_MASK = 0x000000ffffffffffL;    // 求充电或放电的平均时间    public long computeTimePerLevel() {        final long[] steps = mStepDurations;        // 电池信息的总条数        final int numSteps = mNumStepDurations;        // For now we'll do a simple average across all steps.        if (numSteps <= 0) {            return -1;        }        long total = 0;        for (int i=0; i

    public static final int STEP_LEVEL_LEVEL_SHIFT = 40;    public static final long STEP_LEVEL_LEVEL_MASK = 0x0000ff0000000000L;    // 例如 电池信息格式 zD-62-9876543210    public void decodeEntryAt(int index, String value) {        // 获取电池电量        // 例如 value = zD-62-9876543210，得到 level = 0x62,即 98% 的电量        out |= (level << STEP_LEVEL_LEVEL_SHIFT) & STEP_LEVEL_LEVEL_MASK;        long duration = 0;        while (i < N && (c=value.charAt(i)) != '-') {            i++;            duration <<= 4;            if (c >= '0' && c <= '9') {                duration += c - '0';            } else if (c >= 'a' && c <= 'f') {                duration += c - 'a' + 10;            } else if (c >= 'A' && c <= 'F') {                duration += c - 'A' + 10;            }        }        // zD-62-9876543210 对应 0x0203629876543210        mStepDurations[index] = out | (duration & STEP_LEVEL_TIME_MASK);    }