Скачать или смотреть Writing To Internal Storage - Saving Data in Android - raywenderlich.com

Learn how to write files to internal storage. You'll use Gson to convert the app data and peer into the Android file system using Device File Explorer.

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From Android Documentation:
https://developer.android.com/guide/t...

If you don't need to store a lot of data and it doesn't require structure, you should use SharedPreferences. The SharedPreferences APIs allow you to read and write persistent key-value pairs of primitive data types: booleans, floats, ints, longs, and strings.

The key-value pairs are written to XML files that persist across user sessions, even if your app is killed. You can manually specify a name for the file or use per-activity files to save your data.

The API name "shared preferences" is a bit misleading because the API is not strictly for saving "user preferences," such as what ringtone a user has chosen. You can use SharedPreferences to save any kind of simple data, such as the user's high score. However, if you do want to save user preferences for your app, then you should read how to create a settings UI, which uses PreferenceActivity to build a settings screen and automatically persist the user's settings.

To learn how to store any type of key-value data, read Save Key-Value Data with SharedPreferences.

Android provides full support for SQLite databases. Any database you create is accessible only by your app. However, instead of using SQLite APIs directly, we recommend that you create and interact with your databases with the Room persistence library.

The Room library provides an object-mapping abstraction layer that allows fluent database access while harnessing the full power of SQLite.

Although you can still save data directly with SQLite, the SQLite APIs are fairly low-level and require a great deal of time and effort to use. For example:

There is no compile-time verification of raw SQL queries.
As your schema changes, you need to update the affected SQL queries manually. This process can be time consuming and error prone.

You need to write lots of boilerplate code to convert between SQL queries and Java data objects.

The Room persistence library takes care of these concerns for you while providing an abstraction layer over SQLite.

The Android SDK includes a sqlite3 database tool that allows you to browse table contents, run SQL commands, and perform other useful functions on SQLite databases. For more information, see the adb documentation.

Android uses a file system that's similar to disk-based file systems on other platforms. This page describes how to work with the Android file system to read and write files with the File APIs.

A File object works well for reading or writing large amounts of data in start-to-finish order without skipping around. For example, it's good for image files or anything exchanged over a network.

The exact location of the where your files can be saved might vary across devices, so you should use the methods described on this page to access internal and external storage paths instead of using absolute file paths.

To view files on a device, you can log the file location provided by methods such as File.getAbsolutePath(), and then browse the device files with Android Studio's Device File Explorer.

All Android devices have two file storage areas: "internal" and "external" storage. These names come from the early days of Android, when most devices offered built-in non-volatile memory (internal storage), plus a removable storage medium such as a micro SD card (external storage). Many devices now divide the permanent storage space into separate "internal" and "external" partitions. So even without a removable storage medium, these two storage spaces always exist, and the API behavior is the same regardless of whether the external storage is removable.