The android documentation has the following options below but does not explain what circumstances each is best for. What are the pros and cons of each method? e.g. Under what conditions would SQL be better than Shared Preferences?
Shared Preferences
Internal Storage
External Storage
SQLite Databases
Network Connection
Different Storage options in Android
Content Providers
Consider the structured data added to the device from application1 is
not accessible to another application2 present in the same device but
the profile photo added to the device by application1 is available to
the application2 running in the same device
Consider android device as a city, the applications in it are the
houses in the city, people in the houses(application) are the data.
Now content provider is like an broker in the city(android device).
This broker provide access for the people in the city for finding
different houses referring as the content provider in the android
device provide access for the data in the device for different
applications.
Shared Preferences
Consider I have an App say a Face book App which I use to log in to
my account.
Now the very first time I enter my username and password to get
access to my account. Say I log out of the application an hour later
again I use the same Face book App to login again to my application.
I have to enter username and password again to login to my account
and I set a theme to my application and other settings on how my app
looks in my current phone
This is un-necessary because consider I am using my phone to login to
the application. So I will always use my phone to login again and
again, thus entering my credentials again and again is more work
shows it’s not a user friendly app
Shared Preferences is very handy in such scenarios where I can use
its feature to share my data in a xml file Which physically exists in
the Android app installed in my phone which is not destroyed even if
the app is closed. Here we can save user preferences data of the
current application.
As a result next time I open my app in my phone I can see the data
automatically filled in the necessary fields and the settings are
File Storage
In Android we can use the device storage space to store the data in
it for the applications. The type of data involves things such as a
text file, image file, video file, audio file etc.
As seen in the figure as we can see that there are two places we can
do this. One way is to write the raw files into primary /secondary
storage. Another way is to write the cache files into the
primary/secondary storage.
There is also difference between storing raw data and the cache data,
the raw data once stored in memory by user has to be explicitly
deleted by the user explicitly otherwise it would exist till then.
Cache data stored in memory is not a permanent data because the
system automatically deletes it if it feels there is shortage of
memory.
Internal Storage:
Consider a user in an application has stored data in internal
storage, then only that user of that application has access to that
data on the mobile and that data is automatically deleted when the
user uninstalls the application. Speaking of which internal memory is
private.
The apps internal storage directory is stored using the name package
name in a special place in the android file system.
Other apps or users of current app have no access to the file set by
a particular user and a particular app unless it is explicitly made
available to the user for readable/writable access.
SQLite
Sqlite is used to store more structured data locally in a mobile
where the android app is running. Structured data involves as of
which shown in the figure like a student’s information in the form of
rows and columns.
Sqlite offers similar functionality like Mysql and oracle but with
limited functional features. Some of the things involve performing
query operations on tables. There are features though like creating
views but also some features are not available like stored procedure.
Sqlite is very helpful in storing complex and large data which can be
downloaded once and can be used again and again until the application
is running. When the application is closed the sqlite database is
also destroyed.
Putting all the pieces together
Shared preferences are good for storing ... an application's preferences, and other small bits of data. It's a just really simple persistent string key store for a few data types: boolean, float, int, long and string. So for instance if my app had a login, I might consider storing the session key as string within SharedPreferences.
Internal storage is good for storing application data that the user doesn't need access to, because the user cannot easily access internal storage. Possibly good for caching, logs, other things. Anything that only the app intends to Create Read Update or Delete.
External storage. Great for the opposite of what I just said. The dropbox app probably uses external storage to store the user's dropbox folder, so that the user has easy access to these files outside the dropbox application, for instance, using the file manager.
SQLite databases are great whenever you are going to use a lot of structured data and a relatively rigid schema for managing it. Put in layman's terms, SQLite is like MySQL or PostgreSQL except instead of the database acting as a server daemon which then takes queries from the CGI scripts like php, it is simply stored in a .db file, and accessed and queried through a simple library within the application. While SQLite cannot scale nearly as big as the dedicated databases, it is very quick and convenient for smaller applications, like Android apps. I would use an SQLite db if I were making an app for aggregating and downloading recipes, since that kind of data is relatively structured and a database would allow for it to scale well. Databases are nice because writing all of your data to a file, then parsing it back in your own proprietary format it no fun. Then again, storing data in XML or JSON wouldn't be so bad.
Network connection refers to storing data on the cloud. HTTP or FTP file and content transfers through the java.net.* packages makes this happen.
SharedPreferences is mainly for application-specific settings that you can access via your Settings menu - like application settings. It's a good idea to keep everything simple here - mostly boolean flags, short strings, or integers. SharedPreferences data persist on device reboot, and are removed along with app uninstallation. Data is saved as a key-value pair.
Internal Storage is mostly used for larger non-persistent data storage. You utilize internal storage if you want to process an image, a short video clip, a large text file, etc. But you don't store the processed data in the internal storage - its function is more like a CPU's RAM. The amount of available internal storage for your application depends on the device, but it's always a good idea to keep anything under 1MB. Data is referenced via its file path.
External Storage does not only refer to the SDCard storage, but for higher-end phones, this can mean internal mountable storage (like in the Galaxy Nexus or S2). This is where you store the large video files, the high-resolution images, and the 20-megabyte text file you want to parse in your application. This is also a place to store data that you want shared across devices if you swap sd cards. Data is also referenced via its file path.
SQLite Databases is where you'd store pretty much anything you want in a regular database - with the advantage of organizing things into tables, rows, and columns. It works best with things that you want displayed in the UI as lists - the best example would be the great invention knows as the CursorAdapter. Data stored here also persist on device reboot, and are removed with app uninstallation. You can also share data across applications with sqlite db if you hook it up to a ContentProvider. Data is accessed using a Cursor, where you can call methods as if you're executing sql statements.
Network Connection is not really a data storage technique, but can be a way of persisting data for a specific user provided the device is connected to the internet, using some sort of authentication. You have to balance out between downloading data every time the app needs it, or having a one-time data sync, which would ultimately lead to another of the storage options mentioned above.
Shared preferences are key/value pairs, nothing more. So if you want to keep track of say, students and their test score, it really won't work well for that.
A database is just that, a database. You can define as many columns (and tables) as you need to get the job done.
If it's preferences for your app, use shared preferences (almost any preference I can think of can be done that way), if it's anything else more complicated, use a database.
As we all know starting Android Q (API=29) introduced new Scoped Storage concept, which basically prevents access to external files/dirs, except media files. Namely:
Programmer can use internal/app specific storage (no limits) - getFilesDir()
The only external storage can be accessed is via getExternalFilesDir(), but during app uninstall data will be deleted
There's option to access external storage via MediaStore, but it works only for media files
App still can read any external file via: getContentResolver().openInputStream(uri)
In my case I have app, which stores user data in SQLite database in app specific directory, database size can be up-to several gigs.
In all previous versions of my app users used to backup data to external storage/SD/USB and transfer those data to their new device, so they could continue to use data (it's encrypted database containing any kind of private data, including audio/video/documents and so on).
Question: how can I backup this database? I couldn't manage to find appropriate way to save/backup data to any external storage...
P.S. Android autobackup service is unworkable due to the size of database.
I am working on an android app that is storing very important data in local sqlite database. Is there some possibility that data will be lost? I mean beside uninstalling the app or clearing its data
TLDR: there's no 100% safe storage. In practice the actual answer is no.
Like with all storage, there are risks (ordered from more likely to less likely):
Malicious users exploit a vulnerability on the system to mess with your data.
Physical support damage, by either external factors (e.g. radiation, strong electromagnetic fields) or by physical wearing (entropy will eventually win)
Filesystem corruption (e.g. bugs in the filesystem driver)
The only where the data is lost:
1. User clears the appData
2. User Reset's the phone.
So you can store the db file in an external storage with encryption. So the db remains even after the user clears the app data.
The best way to protect the data is to use GDrive integration to backup the db file. So there's always a backup available in the cloud.
I am working on logs inside android, I thought two ways for storing logs, and one is on external directory as a text file or a log file while other is to store in database. I found database method more useful in my case. My question is if I UN-install and reinstall the app will the database will be affected? In case of yes what should I do? I cannot place the logs online. How to take the backup or safe that database so it won’t be affected in case of UN- installation.
My question is if I uninstall and reinstall the app will the database will be affected?
Yes, your database will by default be stored in the application's data directory, which is deleted along with your application on uninstallation.
You can instead write a file of a filetype of your choosing (whether that's a simple text file, or a database file) to the external storage. You can obtain the directory path using:
Environment.getExternalStoragePublicDirectory(type) for obtaining a directory path of files of a specific type, such as images or videos;
Environment.getExternalStorageDirectory() for obtaining the primary external storage directory, under which you could create a new path.
I would nevertheless discourage you from doing this, because it would require your users to manually dispose of any files after uninstalling your application. Perhaps you should reconsider the justification of choosing for this solution.
If you uninstall the app, then the database (and all other data stored in the apps private storage for that matter) will be gone.
You could store your logs in the public external storage, but this will expose your logs to other applications as well as the user.
One possible approach could be to use application private storage for your 'live' logs, and make periodic backups to the public storage. In case of a new installation, you can check your designated backup location and attempt to restore previous logs from the backup.
I have a lite version of an application that uses a SQLite database. I want to copy that database over to the full version of the application when the user installs the full version.
I have written some code to perform the file copy, but the lite database file always comes up as unreadable. The file is there and I can point to it, but I can't read it to perform the copy.
In the Android documentation, we read:
You can save files directly on the
device's internal storage. By default,
files saved to the internal storage
are private to your application and
other applications cannot access them
(nor can the user).
Note the words, "by default".
Is there a way that I can override that default and make the SQLite file readable by my other application?
Thank you.
I believe you have 2 options.
Set the sql database to be world readable on creation. You can do this by setting the appropriate mode parameter in the call to openFileOutput() or openOrCreateDatabase().
Set the sharedUserId attribute in the manifest of both of your applications so that they have the same user ID. This treats both applications as the same user, giving both applications access to the same private set of files.