XxGoliathusxX XxGoliathusxX - 3 months ago 21
Android Question

Android Open and Close Database

I read a lot of discussions here on StackOverflow and also many on websites in the internet about: When should I open and close my sqlite-database.
I have read a wide range of responds and guesses from different periods.
So in the end I'm more confused than before. What people suggested:


  1. Close your db in onDestroy()
    Comments: "OnDestroy() does not get called always! Use onStop()!"
    --> So onStart() has to open it.

  2. The db works efficiently. No need to close it.

  3. Open your db once and create a field and an accessor.

  4. Close after use.



And many more...

So what is correct proceed in 2016? Pls do not guess!

Examplelinks:

Android: opening and closing SQLite database

Android Closing database

Answer

As with lots of things in computer programming, there is no single "correct proceed" for the timing of closing a SQLite database (via close() on SQLiteOpenHelper if you are using that, or close() on SQLiteDatabase otherwise).

The one fairly hard-and-fast rule is to not use multiple SQLiteDatabase objects for the same database across multiple threads at the same time. That can get you in trouble, unless you are doing your own thread synchronization. If you stick to one SQLiteDatabase object per database, thread synchronization is handled inside the SQLiteDatabase.

Because of the one-database-for-all-threads rule, and because in many cases tracking when threads may or may not want the database can be tricky when you have many different components, some developers take the approach of having a singleton database manager, which lazy-opens the database... and never closes it. For example, a database-backed ContentProvider uses this pattern, as a ContentProvider is never destroyed, so there is no clear time when to close the database.

Personally, I would go that route over the open-use-close approach, particularly if you are using SQLCipher for Android (an encrypted SQLite replacement). However, there is nothing especially wrong with the open-use-close approach if you are sure that only one thread at a time will be working with the database.

If only a single component uses the database, there is nothing wrong with triggering opening the database in onCreate() and closing it in onDestroy(). After all, if that is the only component that needs the database, you do not need the database when the component itself goes away.

Close your db in onDestroy() Comments: "OnDestroy() does not get called always! Use onStop()!" --> So onStart() has to open it.

If onDestroy() does not get called on a component, either you crashed with an unhandled exception in that component, or your process was terminated. The latter scenario is not a problem (again, this is how a ContentProvider works, since a provider is never destroyed). The former scenario should not be a problem, so long as you do not accidentally use that older SQLiteDatabase and some newer SQLiteDatabase at the same time across multiple threads.

The db works efficiently. No need to close it.

It is not a matter of efficiency. SQLite is transactional. Failing to close a database is not a problem, as there are no unflushed buffers or something that you have to worry about.

Open your db once and create a field and an accessor.

That has nothing directly to do with when you close a database.

Close after use.

That is a pattern, and done properly it can work.