如果我们想修改字体大小，可以参照Settings中的系统字体大小的值来调整，具体数值在/packages/apps/Settings/res/values/arrays.xml文件的entryvalues_font_size标签中有定义，内容如下：

<string-array name="entryvalues_font_size" translatable="false">
    <item>0.85</item>
    <item>1.0</item>
    <item>1.15</item>
    <item>1.30</item>
</string-array>

顶级目录：/frameworks/base/packages/SettingsProvider/

修改文件：res/values/defaults.xml

+ <fraction name="def_font_scale">85%</fraction>

修改文件：src/com/android/providers/settings/DatabaseHelper.java

private void loadSystemSettings(SQLiteDatabase db) {
         * See: SettingsProvider.UpgradeController#onUpgradeLocked
         */
+		loadFractionSetting(stmt, Settings.System.FONT_SCALE, R.fraction.def_font_scale, 1);
    } finally {
        if (stmt != null) stmt.close();
    }
}