Android源码分析（十五）----GPS冷启动实现原理分析

一：原理分析

1. 主要sendExtraCommand方法中传递两个参数， 根据如下源码可以知道第一个参数传递delete_aiding_data,第二个参数传递null即可。

    @Override
    public boolean sendExtraCommand(String command, Bundle extras) {

        long identity = Binder.clearCallingIdentity();
        boolean result = false;

        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 {
            Log.w(TAG, "sendExtraCommand: unknown command " + command);
        }

        Binder.restoreCallingIdentity(identity);
        return result;
    }

    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;
    }

根据flags值GPS_DELETE_ALL清除数据

static void android_location_GpsLocationProvider_delete_aiding_data(JNIEnv* /* env */,
                                                                    jobject /* obj */,
                                                                    jint flags)
{
    if (sGpsInterface)
        sGpsInterface->delete_aiding_data(flags);
}

    /**
     * Specifies that the next call to start will not use the
     * information defined in the flags. GPS_DELETE_ALL is passed for
     * a cold start.
     */
    void  (*delete_aiding_data)(GpsAidingData flags);

二：实现方式

java层主要代码如下：

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Bundle bundle = null;
locationManager.sendExtraCommand(LocationManager.GPS_PROVIDER, "force_xtra_injection", bundle);
locationManager.sendExtraCommand(LocationManager.GPS_PROVIDER, "force_time_injection", bundle);
//GPS cold start
locationManager.sendExtraCommand(LocationManager.GPS_PROVIDER, "delete_aiding_data", bundle);

所需权限配置如下， 6.0版本可能需要动态申请权限。

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_LOCATION_EXTRA_COMMANDS"/>

喜欢源码分析系列可参考其他文章：
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Android源码分析（三）-----系统框架设计思想
Android源码分析（四）-----Android源码编译及刷机步骤
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