android 5.1 BatteryManager深入分析

BatteryManager主要是去主动查看电池状态，主要通过binder通信去healthd中查看电池的各个属性。

可以看下BatteryManager的主要代码

private long queryProperty(int id) {
    long ret;

    if (mBatteryPropertiesRegistrar == null) {
        IBinder b = ServiceManager.getService("batteryproperties");//这个service就是在healthd中加入ServiceManager中
        mBatteryPropertiesRegistrar =
            IBatteryPropertiesRegistrar.Stub.asInterface(b);//转化接口

        if (mBatteryPropertiesRegistrar == null)
            return Long.MIN_VALUE;
    }

    try {
        BatteryProperty prop = new BatteryProperty();//新建一个数据类型

        if (mBatteryPropertiesRegistrar.getProperty(id, prop) == 0)//prop作为结果返回
            ret = prop.getLong();
        else
            ret = Long.MIN_VALUE;
    } catch (RemoteException e) {
        ret = Long.MIN_VALUE;
    }

    return ret;
}

public int getIntProperty(int id) {
    return (int)queryProperty(id);
}

public long getLongProperty(int id) {
    return queryProperty(id);
}
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}

接下来我们看下healthd中batteryproperties这个service：

void BatteryPropertiesRegistrar::publish() {
defaultServiceManager()->addService(String16(“batteryproperties”), this);//将service加入到serviceManager中
}

void BatteryPropertiesRegistrar::notifyListeners(struct BatteryProperties props) {
Mutex::Autolock _l(mRegistrationLock);
for (size_t i = 0; i < mListeners.size(); i++) {//通知各个注册到healthd中的listener，类似BatteryService中注册到healthd中的listener（binder通信）
mListeners[i]->batteryPropertiesChanged(props);
}
}

void BatteryPropertiesRegistrar::registerListener(const sp& listener) {//注册到healthd的函数，比如BatteryService中，实现一个aidl，然后将这个类的stub实现，发到这边注册
//这样BatteryService中的BatteryLIstener就类似这边的一个server端，把接口发过来，到时候利用notifyListener来进行跨进程调用。
{
if (listener == NULL)
return;
Mutex::Autolock _l(mRegistrationLock);
// check whether this is a duplicate
for (size_t i = 0; i < mListeners.size(); i++) {
if (mListeners[i]->asBinder() == listener->asBinder()) {
return;
}
}

    mListeners.add(listener);
    listener->asBinder()->linkToDeath(this);
}
healthd_battery_update();
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}

status_t BatteryPropertiesRegistrar::getProperty(int id, struct BatteryProperty *val) {
return healthd_get_property(id, val);
}

当BatteryManager中调用getProperty会到healthd中的getProperty，下面我们再详细看看这个函数:

status_t BatteryMonitor::getProperty(int id, struct BatteryProperty *val) {
status_t ret = BAD_VALUE;

val->valueInt64 = LONG_MIN;

switch(id) {
case BATTERY_PROP_CHARGE_COUNTER:
    if (!mHealthdConfig->batteryChargeCounterPath.isEmpty()) {
        val->valueInt64 =
            getIntField(mHealthdConfig->batteryChargeCounterPath);//将结果返回到BatteryProperty对象中
        ret = NO_ERROR;//返回0是没有错
    } else {
        ret = NAME_NOT_FOUND;
    }
    break;

case BATTERY_PROP_CURRENT_NOW:
    if (!mHealthdConfig->batteryCurrentNowPath.isEmpty()) {
        val->valueInt64 =
            getIntField(mHealthdConfig->batteryCurrentNowPath);
        ret = NO_ERROR;
    } else {
        ret = NAME_NOT_FOUND;
    }
    break;

case BATTERY_PROP_CURRENT_AVG:
    if (!mHealthdConfig->batteryCurrentAvgPath.isEmpty()) {
        val->valueInt64 =
            getIntField(mHealthdConfig->batteryCurrentAvgPath);
        ret = NO_ERROR;
    } else {
        ret = NAME_NOT_FOUND;
    }
    break;

case BATTERY_PROP_CAPACITY:
    if (!mHealthdConfig->batteryCapacityPath.isEmpty()) {
        val->valueInt64 =
            getIntField(mHealthdConfig->batteryCapacityPath);
        ret = NO_ERROR;
    } else {
        ret = NAME_NOT_FOUND;
    }
    break;

case BATTERY_PROP_ENERGY_COUNTER:
    if (mHealthdConfig->energyCounter) {
        ret = mHealthdConfig->energyCounter(&val->valueInt64);
    } else {
        ret = NAME_NOT_FOUND;
    }
    break;

default:
    break;
}

return ret;
}
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