【Android】GPS啟動流程及數據流向分析（基於2.3.5）

GPS啟動流程及數據流向分析：

首先在系統init階段，會通過ServiceManager addService添加很多的Service，這其中就包含LocationService。
代碼在SystemServer.java中:

1. try {
2. Slog.i(TAG, "Location Manager");
3. location = new LocationManagerService(context);
4. ServiceManager.addService(Context.LOCATION_SERVICE, location);
5. } catch (Throwable e) {
6. reportWtf("starting Location Manager", e);
7. }

隨後調用LocationManagerService的systemReady函數開啟一個線程。

1. final LocationManagerService locationF = location;
2. try {
3. if (locationF != null) locationF.systemReady();
4. } catch (Throwable e) {
5. reportWtf("making Location Service ready", e);
6. }

--LocationManagerService.java

1. void systemReady() {
2. // we defer starting up the service until the system is ready
3. Thread thread = new Thread(null, this, "LocationManagerService");
4. thread.start();
5. }

在 Thread的run函數中為接收消息做好了准備，並且調用了一個initialize函數：

1. public void run()
2. {
3. Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
4. Looper.prepare();
5. mLocationHandler = new LocationWorkerHandler();
6. initialize();
7. Looper.loop();
8. }

接著看initialize()：

1. private void initialize() {
2. // Create a wake lock, needs to be done before calling loadProviders() below
3. PowerManager powerManager = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
4. mWakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, WAKELOCK_KEY);
6. // Load providers
7. loadProviders();
9. // Register for Network (Wifi or Mobile) updates
10. IntentFilter intentFilter = new IntentFilter();
11. intentFilter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
12. // Register for Package Manager updates
13. intentFilter.addAction(Intent.ACTION_PACKAGE_REMOVED);
14. intentFilter.addAction(Intent.ACTION_PACKAGE_RESTARTED);
15. intentFilter.addAction(Intent.ACTION_QUERY_PACKAGE_RESTART);
16. mContext.registerReceiver(mBroadcastReceiver, intentFilter);
17. IntentFilter sdFilter = new IntentFilter(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
18. mContext.registerReceiver(mBroadcastReceiver, sdFilter);
20. // listen for settings changes
21. ContentResolver resolver = mContext.getContentResolver();
22. Cursor settingsCursor = resolver.query(Settings.Secure.CONTENT_URI, null,
23. "(" + Settings.System.NAME + "=?)",
24. new String[]{Settings.Secure.LOCATION_PROVIDERS_ALLOWED},
25. null);
26. mSettings = new ContentQueryMap(settingsCursor, Settings.System.NAME, true, mLocationHandler);
27. SettingsObserver settingsObserver = new SettingsObserver();
28. mSettings.addObserver(settingsObserver);
29. }