GPS信息的内容提供者

概述

    Provider是提供具体服务功能的抽象，如GPS信息的提供由GpsLocationProvider来完成。通常这是在Java
层的抽象，具体的实现会通过JNI调用底层C++的代码。在GPS Service中讨论过LocationManagerService在启动
时会加载所有可用的Provider，而这里我们主要关心的是实际提供GPS定位信息的实现类GpsLocationProvider。

初始化方法

GpsLocationProvider实现了LocationProviderInterface的接口，其初始化主要完成以下几个功能：
- 创建GpsNetInitiatedHandler处理类，为底层提供net init的回调处理。
- 为接收广播添加了一些过滤条件。
- 读取gps.conf的配置文件，并初始化相关参数。
- 创建循环线程GpsLocationProviderThread，初始化事件处理的Handler。

GpsLocationProvider

public class GpsLocationProvider implements LocationProviderInterface {
    ......
    // 配置文件路径
    private static final String PROPERTIES_FILE = "/system/etc/gps/gps.conf";

    public GpsLocationProvider(Context context, ILocationManager locationManager) {
        ......
        // 创建NI处理的Handler
        mNIHandler = new GpsNetInitiatedHandler(context);

        ......
        // 添加接收广播的过滤条件
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(Intents.DATA_SMS_RECEIVED_ACTION);
        intentFilter.addDataScheme("sms");
        intentFilter.addDataAuthority("localhost","7275");
        context.registerReceiver(mBroadcastReciever, intentFilter);

        intentFilter = new IntentFilter();
        intentFilter.addAction(Intents.WAP_PUSH_RECEIVED_ACTION);
        try {
            intentFilter.addDataType("application/vnd.omaloc-supl-init");
        } catch (IntentFilter.MalformedMimeTypeException e) {
        }
        context.registerReceiver(mBroadcastReciever, intentFilter);

        ......
        // 读取配置文件信息
        mProperties = new Properties();
        try {
            File file = new File(PROPERTIES_FILE);
            FileInputStream stream = new FileInputStream(file);
            mProperties.load(stream);
            stream.close();
            mNtpServer = mProperties.getProperty("NTP_SERVER", null);

            mSuplServerHost = mProperties.getProperty("SUPL_HOST");
            String portString = mProperties.getProperty("SUPL_PORT");
            if (mSuplServerHost != null && portString != null) {
                try {
                    mSuplServerPort = Integer.parseInt(portString);
                } catch (NumberFormatException e) {
                }
            }

            mC2KServerHost = mProperties.getProperty("C2K_HOST");
            portString = mProperties.getProperty("C2K_PORT");
            if (mC2KServerHost != null && portString != null) {
                try {
                    mC2KServerPort = Integer.parseInt(portString);
                } catch (NumberFormatException e) {
                    Log.e(TAG, "unable to parse C2K_PORT: " + portString);
                }
            }
        } catch (IOException e) {
        }

        // 创建线程
        mThread = new GpsLocationProviderThread();
        mThread.start();
        ...... 
    }
}

GpsLocationProviderThread

private final class GpsLocationProviderThread extends Thread {
    public GpsLocationProviderThread() {
        super("GpsLocationProvider");
    }

    public void run() {
        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
        initialize();
        Looper.prepare();
        mHandler = new ProviderHandler();
        // signal when we are initialized and ready to go
        mInitializedLatch.countDown();
        Looper.loop();
    }
}

配置文件

上面分析了Provider在初始化时会读取一个配置文件，该配置文件通常会被拷贝到一个固定目录，由该类去解析。解析后的配置参数会涉及到时间同步、辅助数据下载、AGPS设定等等。
主要配置以下几个属性：

全局设定

属性	默认值	描述
NTP_SERVER	xtra1.gpsonextra.net	NTP服务器地址
XTRA_SERVER_1	http://xtra1.gpsonextra.net/xtra.bin	辅助数据的下载地址1
XTRA_SERVER_2	http://xtra2.gpsonextra.net/xtra.bin	辅助数据的下载地址2
XTRA_SERVER_3	http://xtra3.gpsonextra.net/xtra.bin	辅助数据的下载地址3
INTERMEDIATE_POS	0
ACCURACY_THRES	5000
ENABLE_WIPER	1	是否开启支持wifi定位

AGPS服务器设定：

属性	默认值	描述
SUPL_HOST	supl.google.com	SUPL服务器地址
SUPL_PORT	7275	SUPL服务器端口
APN_NAME	3gwap	APN名称
AGPS_TYPE	default,supl	AGPS的类型
C2K_HOST	c2k.pde.com	C2K服务器地址
C2K_PORT	1234	C2K服务器端口

配置文件示例

NTP_SERVER=xtra1.gpsonextra.net
XTRA_SERVER_1=http://xtra1.gpsonextra.net/xtra.bin
XTRA_SERVER_2=http://xtra2.gpsonextra.net/xtra.bin
XTRA_SERVER_3=http://xtra3.gpsonextra.net/xtra.bin

# Intermediate position report, 1=enable, 0=disable
INTERMEDIATE_POS=0

# Accuracy threshold for intermediate positions 
# less accurate positions are ignored, 0 for passing all positions
ACCURACY_THRES=5000

# Wiper (wifi positioning), 1=enable, 0=disable
ENABLE_WIPER=1

################################
##### AGPS server settings #####
################################

# FOR SUPL SUPPORT, set the following
SUPL_HOST=supl.google.com
SUPL_PORT=7275
APN_NAME=3gwap
AGPS_TYPE=default,supl

# FOR C2K PDE SUPPORT, set the following
C2K_HOST=c2k.pde.com
C2K_PORT=1234

处理定位请求

当Service发送定位请求后，实际会调用到该Provider的startNavigating方法。
当Service发送停止定位的请求后，实际会调用到该Provider的stopNavigating方法。
这里需要注意的是GPS定位的几种类型和处理方式，主要分为GPS和APGS两种。这些设置通常在Settings中设定。
处理定位的功能通常由底层的驱动完成，这里是通过JNI调用实现。

GPS类型

类型标识	辅助支持(AGPS)
GPS_POSITION_MODE_STANDALONE	否
GPS_POSITION_MODE_MS_ASSISTED	是
GPS_POSITION_MODE_MS_BASED	是

startNavigating

private void startNavigating(boolean singleShot) {
    if (!mStarted) {
        mStarted = true;
        mSingleShot = singleShot;
        // 默认为GPS_POSITION_MODE_STANDALONE，以下是通过Setting动态改变设定
        mPositionMode = GPS_POSITION_MODE_STANDALONE;

         if (Settings.Secure.getInt(mContext.getContentResolver(),
                Settings.Secure.ASSISTED_GPS_ENABLED, 1) != 0) {
            if (singleShot && hasCapability(GPS_CAPABILITY_MSA)) {
                mPositionMode = GPS_POSITION_MODE_MS_ASSISTED;
            } else if (hasCapability(GPS_CAPABILITY_MSB)) {
                mPositionMode = GPS_POSITION_MODE_MS_BASED;
            }
        }

        // 设置定位模式
        int interval = (hasCapability(GPS_CAPABILITY_SCHEDULING) ? mFixInterval : 1000);
        if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
                interval, 0, 0)) {
            mStarted = false;
            return;
        }
        // 开始定位
        if (!native_start()) {
            mStarted = false;
            return;
        }
        ...... 
    }
}

stopNavigating

private void stopNavigating() {
    if (mStarted) {
        ......
        native_stop();
        
        ......
        // 更新状态
        updateStatus(LocationProvider.TEMPORARILY_UNAVAILABLE, 0);
    }
}

报告定位信息

定位信息的获取是通过reportLocation方法实现，它实际上是注册给JNI接口的回调函数，当底层获取到定位信息后，通过该回调向上层传递。这里需要注意的是不同类型的信息，其处理方式也不一样，主要分为以下几种：
- 定位信息：通过Service的reportLocation方法处理。
- 状态信息：通过注册的GpsStatusListener处理。
- 已接收TTFF：通过广播通知其他进程定位成功。

reportLocation

private void reportLocation(int flags, double latitude, double longitude, 
                            double altitude, float speed, float bearing, 
                            float accuracy, long timestamp) {
    synchronized (mLocation) {
        mLocationFlags = flags;
        if ((flags & LOCATION_HAS_LAT_LONG) == LOCATION_HAS_LAT_LONG) {
            mLocation.setLatitude(latitude);
            mLocation.setLongitude(longitude);
            mLocation.setTime(timestamp);
        }
        if ((flags & LOCATION_HAS_ALTITUDE) == LOCATION_HAS_ALTITUDE) {
            mLocation.setAltitude(altitude);
        } else {
            mLocation.removeAltitude();
        }
        if ((flags & LOCATION_HAS_SPEED) == LOCATION_HAS_SPEED) {
            mLocation.setSpeed(speed);
        } else {
            mLocation.removeSpeed();
        }
        if ((flags & LOCATION_HAS_BEARING) == LOCATION_HAS_BEARING) {
            mLocation.setBearing(bearing);
        } else {
            mLocation.removeBearing();
        }
        if ((flags & LOCATION_HAS_ACCURACY) == LOCATION_HAS_ACCURACY) {
            mLocation.setAccuracy(accuracy);
        } else {
            mLocation.removeAccuracy();
        }

        try {
            // 调用Service的reportLocation方法
            mLocationManager.reportLocation(mLocation, false);
        } catch (RemoteException e) {
        }
    }

    mLastFixTime = System.currentTimeMillis();
    if (mTTFF == 0 && (flags & LOCATION_HAS_LAT_LONG) == LOCATION_HAS_LAT_LONG) {
        mTTFF = (int)(mLastFixTime - mFixRequestTime);

        // 通过回调处理TTFF信息
        synchronized(mListeners) {
            int size = mListeners.size();
            for (int i = 0; i < size; i++) {
                Listener listener = mListeners.get(i);
                try {
                    listener.mListener.onFirstFix(mTTFF); 
                } catch (RemoteException e) {
                    mListeners.remove(listener);
                    size--;
                }
            }
        }
    }

    ...... 
    // 通过Intent通知已获取TTFF
    if (mStarted && mStatus != LocationProvider.AVAILABLE) {
        ......
        Intent intent = new Intent(LocationManager.GPS_FIX_CHANGE_ACTION);
        intent.putExtra(LocationManager.EXTRA_GPS_ENABLED, true);
        mContext.sendBroadcast(intent);
        updateStatus(LocationProvider.AVAILABLE, mSvCount);
    }
    ...... 
}

处理Service命令

之前在GPS服务中提到，LocationManagerService可向Provider发送三种类型的命令：
- 删除辅助数据：需要设置删除的数据类型，并调用native_delete_aiding_data实现。
- 同步时间：通过SntpClient获取时间后，调用native_inject_time实现。
- 下载辅助数据：通过GpsXtraDownloader类实现下载功能，获取数据后通过native_inject_xtra_data将数据传给底层。

sendExtraCommand

public boolean sendExtraCommand(String command, Bundle extras) {
    ......
    if ("delete_aiding_data".equals(command)) {
        result = deleteAidingData(extras);
    } else if ("force_time_injection".equals(command)) {
        sendMessage(INJECT_NTP_TIME, 0, null);
        result = true;
    } else if ("force_xtra_injection".equals(command)) {
        if (mSupportsXtra) {
            xtraDownloadRequest();
            result = true;
        }
    } else {
    }
    ......    
}

deleteAidingData

private boolean deleteAidingData(Bundle extras) {
    int flags;

    if (extras == null) {
        flags = GPS_DELETE_ALL;
    } else {
        flags = 0;
        if (extras.getBoolean("ephemeris")) flags |= GPS_DELETE_EPHEMERIS;
        if (extras.getBoolean("almanac")) flags |= GPS_DELETE_ALMANAC;
        if (extras.getBoolean("position")) flags |= GPS_DELETE_POSITION;
        if (extras.getBoolean("time")) flags |= GPS_DELETE_TIME;
        if (extras.getBoolean("iono")) flags |= GPS_DELETE_IONO;
        if (extras.getBoolean("utc")) flags |= GPS_DELETE_UTC;
        if (extras.getBoolean("health")) flags |= GPS_DELETE_HEALTH;
        if (extras.getBoolean("svdir")) flags |= GPS_DELETE_SVDIR;
        if (extras.getBoolean("svsteer")) flags |= GPS_DELETE_SVSTEER;
        if (extras.getBoolean("sadata")) flags |= GPS_DELETE_SADATA;
        if (extras.getBoolean("rti")) flags |= GPS_DELETE_RTI;
        if (extras.getBoolean("celldb-info")) flags |= GPS_DELETE_CELLDB_INFO;
        if (extras.getBoolean("all")) flags |= GPS_DELETE_ALL;
    }

    if (flags != 0) {
        native_delete_aiding_data(flags);
        return true;
    }

    return false;
}

handleInjectNtpTime

private void handleInjectNtpTime() {
    ......
    SntpClient client = new SntpClient();
    long delay;

    if (client.requestTime(mNtpServer, 10000)) {
        long time = client.getNtpTime();
        long timeReference = client.getNtpTimeReference();
        int certainty = (int)(client.getRoundTripTime()/2);
        long now = System.currentTimeMillis();

        native_inject_time(time, timeReference, certainty);
        delay = NTP_INTERVAL;
    } else {
        delay = RETRY_INTERVAL;
    }
    ......
}

handleDownloadXtraData

private void handleDownloadXtraData() {
    ......
    GpsXtraDownloader xtraDownloader = new GpsXtraDownloader(mContext, mProperties);
    byte[] data = xtraDownloader.downloadXtraData();
    if (data != null) {
        native_inject_xtra_data(data, data.length);
    } else {
        ......
    }
}

内部消息处理Handler

ProviderHandler提供了该Provider线程消息的处理机制，通常在提供给上层调用的接口中发送相应的处理消息，并通过系列的handle*方法处理。例如上面提到的下载辅助数据的命令便是通过该机制实现。

ProviderHandler

private final class ProviderHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        int message = msg.what;
        switch (message) {
            case ENABLE:
                if (msg.arg1 == 1) {
                    handleEnable();
                } else {
                    handleDisable();
                }
                break;
            case ENABLE_TRACKING:
                handleEnableLocationTracking(msg.arg1 == 1);
                break;
            case REQUEST_SINGLE_SHOT:
                handleRequestSingleShot();
                break;
            case UPDATE_NETWORK_STATE:
                handleUpdateNetworkState(msg.arg1, (NetworkInfo)msg.obj);
                break;
            case INJECT_NTP_TIME:
                handleInjectNtpTime();
                break;
            case DOWNLOAD_XTRA_DATA:
                if (mSupportsXtra) {
                    handleDownloadXtraData();
                }
                break;
            case UPDATE_LOCATION:
                handleUpdateLocation((Location)msg.obj);
                break;
            case ADD_LISTENER:
                handleAddListener(msg.arg1);
                break;
            case REMOVE_LISTENER:
                handleRemoveListener(msg.arg1);
                break;
        }
        ...... 
    }
};

GPS包含哪些信息

使用delete_aiding_data功能时需要设置删除的数据类型，从这里我们知道GPS具体包含哪些信息，如下表。
通常用户在使用GPS时，接收到的数据信息是有时效的，因此不同情况下启动GPS便会分为几种方式：cold start、warm start、hot start。

类型信息表

类型标识	字符串	描述
GPS_DELETE_EPHEMERIS	"ephemeris"	删除星历数据
GPS_DELETE_ALMANAC	"almanac"	删除历书数据
GPS_DELETE_POSITION	"position"	删除位置数据
GPS_DELETE_TIME	"time"	删除时间数据
GPS_DELETE_IONO	"iono"
GPS_DELETE_UTC	"utc"
GPS_DELETE_HEALTH	"health"
GPS_DELETE_SVDIR	"svdir"
GPS_DELETE_SVSTEER	"svsteer"
GPS_DELETE_SADATA	"sadata"
GPS_DELETE_RTI	"rti"
GPS_DELETE_CELLDB_INFO	"celldb-info"
GPS_DELETE_ALL	"all"	删除所有数据

GPS启动方式

启动方式	数据有效性	描述
cold start	删除ephemeris、position、time
warm start	删除ephemeris
hot start	不删除任何数据