Android/Java: accessing the same SQLite DB object from multiple activities

Question

I have a central database in my application that a few different activities need to access.

Should I share this object by making it static? Like for example in the activity that initializes the DB I do this:

protected static appDatabase db;

Then others can access it via FirstActivity.db.

Another option is to create private appDatabase db objects in every activity that needs it, but I suspect opening multiple db objects to access the same stored data may be wasteful.

However I don't know too much about java which is why I'm asking - what's the preferred way to do this, and why?

Thanks

In my application I doesnt use static on such objects. Maybe its prefered, but I haven't done it. Interesting to see whcih answers you get. — Tobias Moe Thorstensen
– Tobias Moe Thorstensen, Commented Jan 6, 2013 at 19:46
I usually work with databases behind ContentProvider in my professional environment and have come to find that ensuring only one database connection exists at a time (using a singleton pattern as @fge suggests) helps me deal with some data consistency issues and avoid "sqlite misuse exceptions". I wonder how these argument hold in a non-ContentProvider environment and therefore upvoted your question. Maybe the person that answers your question can also mention how big performance benefits we can expect with multiple vs single connections? :D — baske
– baske, Commented Jan 6, 2013 at 20:02
Singleton sounds like a good way to go. I have this class "appDatabase" which is a custom SQLite wrapper I made specifically for my purposes. Turning that into a singleton seems like the right solution. — JDS
– JDS, Commented Jan 6, 2013 at 20:12

Mert · Accepted Answer · 2013-01-06 20:28:51Z

You can use singleton like this;

    private static DataHelper singleton;

    public static DataHelper getDataHelper(Context context) {
            if (singleton == null) {
                    singleton = new DataHelper(context);
                    OpenHelper openHelper = new OpenHelper(singleton.context);
                    singleton.db = openHelper.getWritableDatabase();
            }
            if(!singleton.db.isOpen()){
                    OpenHelper openHelper = new OpenHelper(singleton.context);
                    singleton.db = openHelper.getWritableDatabase();
            }
            singleton.context = context;
            return singleton;
    }

    private DataHelper(Context context) {
        this.context = context;
}

And call your singleton class like this;

public DataHelper dh;
this.dh = DataHelper.getDataHelper(this);

Brian Butterfield · Accepted Answer · 2013-01-06 21:18:34Z

I handle this situation using the Application class and synchronized database object management. Here is an example. The [synchronized] qualifier is key in a multithreaded app.

By definition the Application object is Singleton in Android.

public class App extends Application
{

private static App _instance;
private AppLocalStorage _localStorage;

@Override
public void onCreate()
{
    super.onCreate();

    _instance = this;
}


public static App getInstance()
{
        //Exposes a mechanism to get an instance of the 
        //custom application object.
        return _instance;
}

public synchronized AppLocalStorage getDatabase()
{
    if (_localStorage == null)
    {
        _localStorage = new AppLocalStorage(this);
    }

    return _localStorage;
}

}

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