設定Settings的預設值有兩種方式

A. 在獲取是有一個介面可以進行預設值設定，當資料庫中查詢不到該值時，就會返回傳入的預設值。

public static int getInt(ContentResolver cr, String name, int def) {
            return getIntForUser(cr, name, def, cr.getUserId());
        }

其中int def就是要寫入的預設值。

B. 在SettingProvider中進行設定，也就是寫入到資料庫中

首先，在SettingsProvider/res/values/defaults.xml中寫入Settings中的值對應的預設值，例如：

./packages/SettingsProvider/res/values/defaults.xml:40:    <bool name="def_wifi_display_on">false</bool>

然後在DatabaseHelper.java中建立完資料庫進行預設值的插入

./packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java:2559:            loadBooleanSetting(stmt, Settings.Global.WIFI_DISPLAY_ON,R.bool.def_wifi_display_on);

該插入的流程為：

onCreate(SQLiteDatabase db) -> loadSettings(db) -> loadSystemSettings(db);loadSecureSettings(db);loadGlobalSettings(db);

原始碼如下：

public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE system (" +
                    "_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                    "name TEXT UNIQUE ON CONFLICT REPLACE," +
                    "value TEXT" +
                    ");");
        db.execSQL("CREATE INDEX systemIndex1 ON system (name);");

        createSecureTable(db);

        // Only create the global table for the singleton 'owner/system' user
        if (mUserHandle == UserHandle.USER_SYSTEM) {
            createGlobalTable(db);
        }

        db.execSQL("CREATE TABLE bluetooth_devices (" +
                    "_id INTEGER PRIMARY KEY," +
                    "name TEXT," +
                    "addr TEXT," +
                    "channel INTEGER," +
                    "type INTEGER" +
                    ");");

        db.execSQL("CREATE TABLE bookmarks (" +
                    "_id INTEGER PRIMARY KEY," +
                    "title TEXT," +
                    "folder TEXT," +
                    "intent TEXT," +
                    "shortcut INTEGER," +
                    "ordering INTEGER" +
                    ");");

        db.execSQL("CREATE INDEX bookmarksIndex1 ON bookmarks (folder);");
        db.execSQL("CREATE INDEX bookmarksIndex2 ON bookmarks (shortcut);");

        // Populate bookmarks table with initial bookmarks
        boolean onlyCore = false;
        try {
            onlyCore = IPackageManager.Stub.asInterface(ServiceManager.getService(
                    "package")).isOnlyCoreApps();
        } catch (RemoteException e) {
        }
        if (!onlyCore) {
            loadBookmarks(db);
        }

        // Load initial volume levels into DB
        loadVolumeLevels(db);

        // Load inital settings values
        loadSettings(db);

private void loadSettings(SQLiteDatabase db) {
        loadSystemSettings(db);
        loadSecureSettings(db);
        // The global table only exists for the 'owner/system' user
        if (mUserHandle == UserHandle.USER_SYSTEM) {
            loadGlobalSettings(db);
        }
    }

private void loadGlobalSettings(SQLiteDatabase db) {
        SQLiteStatement stmt = null;
        try {
            stmt = db.compileStatement("INSERT OR IGNORE INTO global(name,value)"
                    + " VALUES(?,?);");

            // --- Previously in 'system'
            loadBooleanSetting(stmt, Settings.Global.AIRPLANE_MODE_ON,
                    R.bool.def_airplane_mode_on);

            loadBooleanSetting(stmt, Settings.Global.THEATER_MODE_ON,
                    R.bool.def_theater_mode_on);

            loadStringSetting(stmt, Settings.Global.AIRPLANE_MODE_RADIOS,
                    R.string.def_airplane_mode_radios);

            loadStringSetting(stmt, Settings.Global.AIRPLANE_MODE_TOGGLEABLE_RADIOS,
                    R.string.airplane_mode_toggleable_radios);

            loadBooleanSetting(stmt, Settings.Global.ASSISTED_GPS_ENABLED,
                    R.bool.assisted_gps_enabled);
            .....
            loadBooleanSetting(stmt, Settings.Global.WIFI_DISPLAY_ON,
                    R.bool.def_wifi_display_on);
            ......
}