Android开发笔记-ch3.2.2 Saving Data/Settings & File

3.2.2 Saving Data/Settings & File

Refer to Android lessons for saving data. Common cases are:

• Saving key-value pairs of simple data types in a shared preferences file
• Saving arbitrary files in Android's file system
• Using databases managed by SQLite =>refer to http://developer.android.com/training/basics/data-storage/databases.html

Applications often include settings that allow users to modify app features and behaviors. To provide settings for app, use Android's Preference APIs to build an interface that's consistent with the user experience in other Android apps (including the system settings).

This SO post talks about how to save JSON with SharedPreferences, by doing this:

Saving json to SharedPreferences:

PreferenceManager.getDefaultSharedPreferences(context).edit()
putString("theJson",jsonObject.toString()).apply();

Getting the stored json:

JsonObject jsonObject = PreferenceManager.
getDefaultSharedPreferences(this).getString("theJson","");

Here is from codeproject which illustrate several way for managing data in Android, with sample and source code.

Here is about Android file security. Avoid using external storage/SD card.

The preference file is xml file stored under /data/data/package_name/shared_prefs. It's readable with root. Might need to encrypt it.

For saving to SD card, refer to this SO and Environment: don't be confused by the word "external" here. This directory can better be thought as media/shared storage. It is a filesystem that can hold a relatively large amount of data and that is shared across all applications (does not enforce permissions). Traditionally this is an SD card, but it may also be implemented as built-in storage in a device that is distinct from the protected internal storage and can be mounted as a filesystem on a computer.

To distinguish whether "Environment.getExternalStorageDirectory()" actually returned physically internal or external storage, call Environment.isExternalStorageEmulated(). If it's emulated, than it's internal. On newer devices that have internal storage and sdcard slot Environment.getExternalStorageDirectory() will always return the internal storage. While on older devices that have only sdcard as a media storage option it will always return the sdcard. Some suggests to use following code for access internal and external SD cards:

System.getenv("EXTERNAL_STORAGE")  =>/storage/emulated/legacy
System.getenv("SECONDARY_STORAGE") =>/storage/extSdCarcd
Note, Environment.getExternalStorageDirectory return ref of File. To get the path, append '.getAbsolutePath()'.

Refer to getFilesDir() vs Environment.getDataDirectory(). A detail list is here.