BatteryService分析​

一. BatteryService分析​

电池的信息，电压，温度，充电状态等等，都是由BatteryService来提供的。BatteryService是跑在system_process当中，在系统初始化的时候启动，如下

在BatteryService.java中：
Log.i(TAG, “Starting Battery Service.”);
BatteryService battery = new BatteryService(context);
ServiceManager.addService(“battery”, battery);
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1. 数据来源
BatteryService通过JNI（com_android_server_BatteryService.cpp）读取数据。BatteryService通过JNI注册的不仅有函数，还有变量。 如下：

//##############在BatteryService.java中声明的变量################
private boolean mAcOnline;
private boolean mUsbOnline;
private int mBatteryStatus;
private int mBatteryHealth;
private boolean mBatteryPresent;
private int mBatteryLevel;
private int mBatteryVoltage;
private int mBatteryTemperature;
private String mBatteryTechnology;

// 在BatteryService.java中声明的变量，在com_android_server_BatteryService.cpp中共 用，即 在com_android_server_BatteryService.cpp中其实操作的也是BatteryService.java中声明的变量

gFieldIds.mAcOnline = env->GetFieldID(clazz, “mAcOnline”, “Z”);
gFieldIds.mUsbOnline = env->GetFieldID(clazz, “mUsbOnline”, “Z”);
gFieldIds.mBatteryStatus = env->GetFieldID(clazz, “mBatteryStatus”, “I”);
gFieldIds.mBatteryHealth = env->GetFieldID(clazz, “mBatteryHealth”, “I”);
gFieldIds.mBatteryPresent = env->GetFieldID(clazz, “mBatteryPresent”, “Z”);
gFieldIds.mBatteryLevel = env->GetFieldID(clazz, “mBatteryLevel”, “I”);
gFieldIds.mBatteryTechnology = env->GetFieldID(clazz, “mBatteryTechnology”, “Ljava/lang/String;”);
gFieldIds.mBatteryVoltage = env->GetFieldID(clazz, “mBatteryVoltage”, “I”);
gFieldIds.mBatteryTemperature = env->GetFieldID(clazz, “mBatteryTemperature”, “I”);

//上面这些变量的值，对应是从下面的文件中读取的，一只文件存储一个数值。
#define AC_ONLINE_PATH “/sys/class/power_supply/ac/online”
#define USB_ONLINE_PATH “/sys/class/power_supply/usb/online”
#define BATTERY_STATUS_PATH “/sys/class/power_supply/battery/status”
#define BATTERY_HEALTH_PATH “/sys/class/power_supply/battery/health”
#define BATTERY_PRESENT_PATH “/sys/class/power_supply/battery/present”
#define BATTERY_CAPACITY_PATH “/sys/class/power_supply/battery/capacity”
#define BATTERY_VOLTAGE_PATH “/sys/class/power_supply/battery/batt_vol”
#define BATTERY_TEMPERATURE_PATH “/sys/class/power_supply/battery/batt_temp”
#define BATTERY_TECHNOLOGY_PATH “/sys/class/power_supply/battery/technology”

Android是运行在Linux内核上面的，/sys/class/power_supply亦是Linux内核下面的目录。至于这些文件时怎么生成的，则是由Platform来控制的。

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2. 数据传送
电池的这些信息是通过何种方式，被其他应用所获得的。可以想到的有两种方式，第一种，应用主动从BatteryService获得数据；第二种，BatteryService主动把数据传送给所关心的应用程序。

BatteryService采用的是第二种方式，所有的电池的信息数据是通过Intent传送出去的。在BatteryService.java中，Code如下：

Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);

intent.putExtra(“status”, mBatteryStatus);
intent.putExtra(“health”, mBatteryHealth);
intent.putExtra(“present”, mBatteryPresent);
intent.putExtra(“level”, mBatteryLevel);
intent.putExtra(“scale”, BATTERY_SCALE);
intent.putExtra(“icon-small”, icon);
intent.putExtra(“plugged”, mPlugType);
intent.putExtra(“voltage”, mBatteryVoltage);
intent.putExtra(“temperature”, mBatteryTemperature);
intent.putExtra(“technology”, mBatteryTechnology);

ActivityManagerNative.broadcastStickyIntent(intent, null);

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3. 数据接收
应用如果想要接收到BatteryService发送出来的电池信息，则需要注册一个Intent为Intent.ACTION_BATTERY_CHANGED的BroadcastReceiver。

注册方法如下：
IntentFilter mIntentFilter = new IntentFilter();
mIntentFilter.addAction(Intent.ACTION_BATTERY_CHANGED);
registerReceiver(mIntentReceiver, mIntentFilter);

private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
String action = intent.getAction();
if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {

int nVoltage = intent.getIntExtra(“voltage”, 0);
if(nVoltage!=0){
mVoltage.setText(“V: ” + nVoltage + “mV – Success…”);
}
else

{
mVoltage.setText(“V: ” + nVoltage + “mV – fail…”);
}
}
}
};

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4. 数据更新
电池的信息会随着时间不停变化，自然地，就需要考虑如何实时的更新电池的数据信息。在BatteryService启动的时候，会同时通过UEventObserver启动一个onUEvent Thread。

每一个Process最多只能有一个onUEvent Thread，即使这个Process中有多个UEventObserver的实例。当在一个Process中，第一次Call startObserving()方法后，这个UEvent thread就启动了。
而一旦这个UEvent thread启动之后，就不会停止。

//在BatteryService.java中
mUEventObserver.startObserving(“SUBSYSTEM=power_supply”);

private UEventObserver mUEventObserver = new UEventObserver() {
@Override
public void onUEvent(UEventObserver.UEvent event) {
update();
}
};
在UEvent thread中会不停调用 update()方法，来更新电池的信息数据。

二 . 应用实例

这里介绍电池信息的取得.
    android.content.BroadcastReceiver类
    android.os.BatteryManager类

● 电池信息的取得，调用registerReceiver()方法。

         第1个参数，设置BroadcastReceiver实例
         第2个参数，设置追加了Intent.ACTION_BATTERY_CHANGED处理的IntentFilter实例。

● 在BroadcastReceiver的onReceive()事件，接收到的Intent.ACTION_BATTERY_CHANGED，包括下面的信息。
    “status”（int类型）…状态，定义值是BatteryManager.BATTERY_STATUS_XXX。
    “health”（int类型）…健康，定义值是BatteryManager.BATTERY_HEALTH_XXX。
    “present”（boolean类型）
    “level”（int类型）…电池剩余容量
    “scale”（int类型）…电池最大值。通常为100。
    “icon-small”（int类型）…图标ID。
    “plugged”（int类型）…连接的电源插座，定义值是BatteryManager.BATTERY_PLUGGED_XXX。
    “voltage”（int类型）…mV。
    “temperature”（int类型）…温度，0.1度单位。例如 表示197的时候，意思为19.7度。  
    “technology”（String类型）…电池类型，例如，Li-ion等等。

 

实例代码如下：

import android.app.Activity;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import android.os.BatteryManager;

import android.os.Bundle;

import android.widget.TextView;

 

public class Power extends Activity

{

private TextView m_txtMsg;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

m_txtMsg = (TextView) findViewById(R.id.TXT_MSG);

}

 

@Override

protected void onResume()

{

super.onResume();

 

IntentFilter filter = new IntentFilter();

 

filter.addAction(Intent.ACTION_BATTERY_CHANGED);

registerReceiver(mBroadcastReceiver, filter);

}

 

@Override

protected void onPause()

{

super.onPause();

 

unregisterReceiver(mBroadcastReceiver);

}

 

private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver()

{

@Override

public void onReceive(Context context, Intent intent)

{

String action = intent.getAction();

if (action.equals(Intent.ACTION_BATTERY_CHANGED))

{

int status = intent.getIntExtra("status", 0);

int health = intent.getIntExtra("health", 0);

boolean present = intent.getBooleanExtra("present", false);

int level = intent.getIntExtra("level", 0);

int scale = intent.getIntExtra("scale", 0);

int icon_small = intent.getIntExtra("icon-small", 0);

int plugged = intent.getIntExtra("plugged", 0);

int voltage = intent.getIntExtra("voltage", 0);

int temperature = intent.getIntExtra("temperature", 0);

String technology = intent.getStringExtra("technology");

 

String statusString = "";

 

switch (status)

{

case BatteryManager.BATTERY_STATUS_UNKNOWN:

statusString = "unknown";

break;

case BatteryManager.BATTERY_STATUS_CHARGING:

statusString = "charging";

break;

case BatteryManager.BATTERY_STATUS_DISCHARGING:

statusString = "discharging";

break;

case BatteryManager.BATTERY_STATUS_NOT_CHARGING:

statusString = "not charging";

break;

case BatteryManager.BATTERY_STATUS_FULL:

statusString = "full";

break;

}

 

String healthString = "";

 

switch (health)

{

case BatteryManager.BATTERY_HEALTH_UNKNOWN:

healthString = "unknown";

break;

case BatteryManager.BATTERY_HEALTH_GOOD:

healthString = "good";

break;

case BatteryManager.BATTERY_HEALTH_OVERHEAT:

healthString = "overheat";

break;

case BatteryManager.BATTERY_HEALTH_DEAD:

healthString = "dead";

break;

case BatteryManager.BATTERY_HEALTH_OVER_VOLTAGE:

healthString = "voltage";

break;

case BatteryManager.BATTERY_HEALTH_UNSPECIFIED_FAILURE:

healthString = "unspecified failure";

break;

}

 

String acString = "";

 

switch (plugged)

{

case BatteryManager.BATTERY_PLUGGED_AC:

acString = "plugged ac";

break;

case BatteryManager.BATTERY_PLUGGED_USB:

acString = "plugged usb";

break;

}

String log = "status = " + statusString + "/n"

+ "health = " + healthString + "/n"

+ "present = " + String.valueOf(present) + "/n"

+ "level = " + String.valueOf(level) + "/n"

+ "scale = " + String.valueOf(scale) + "/n"

+ "icon_small = "+ String.valueOf(icon_small) + "/n"

+ "plugged = " + acString + "/n"

//+ "voltage = " + String.valueOf(voltage) + "/n"

+ "voltage = " + Integer.toString(voltage) + "/n"

+ "temperature = " + String.valueOf(temperature) + "/n"

+ "technology = "+ technology;

m_txtMsg.setText(log);

}

}

};

}