作用: 可以偷懒 少写一个文件名和模式

private static String getDefaultSharedPreferencesName(Context context) {return context.getPackageName() + "_preferences";
}
/*** Gets a SharedPreferences instance that points to the default file that is* used by the preference framework in the given context.* * @param context The context of the preferences whose values are wanted.* @return A SharedPreferences instance that can be used to retrieve and*         listen to values of the preferences.*/
public static SharedPreferences getDefaultSharedPreferences(Context context) {return context.getSharedPreferences(getDefaultSharedPreferencesName(context),getDefaultSharedPreferencesMode());
}