Managing database connections in an Android Activity
- by Daniel Lew
I have an application with a ListActivity that uses a CursorAdapter as its adapter. The ListActivity opens the database and does the querying for the CursorAdapter, which is all well and good, but I am having issues with figuring out when to close both the Cursor and the SQLiteDatabase.
The way things are handled right now, if the user finishes the activity, I close the database and the cursor. However, this still ends up with the DalvikVM warning me that I've left a database open - for example, if the user hits the "home" button (leaving the activity in the task's stack), rather than the "back" button.
If I close them during pause and then re-query during resume, then I don't get any errors, but then a user cannot return to the list without it requerying (and thus losing the user's place in the list). By this I mean, the user can click on any item in the list and open a new activity based on it, but will often want to hit "back" afterwards and return to the same place on the list. If I requery, then I cannot return the user back to the correct spot.
What is the proper way to handle this issue? I want the list to remain scrolled properly, but I don't want the VM to keep complaining about unclosed databases.
Edit: Here's a general outline of how I handle the code at the moment:
public class MyListActivity extends ListActivity {
private Cursor mCursor;
private CursorAdapter mAdapter;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mAdapter = new MyCursorAdapter(this);
setListAdapter(mAdapter);
}
protected void onPause() {
super.onPause();
if (isFinishing()) {
mCursor.close();
}
}
protected void onDestroy() {
super.onDestroy();
mCursor.close();
}
private void updateQuery() {
// If we had a cursor open before, close it.
if (mCursor != null) {
mCursor.close();
}
MyDbHelper dbHelper = new MyDbHelper(this);
SQLiteDatabase db = dbHelper.getReadableDatabase();
mCursor = db.query(...);
mAdapter.changeCursor(mCursor);
db.close();
}
}
updateQuery() can be called multiple times because the user can filter the results via menu items (I left this part out of the code, as the problem still occurs even if the user does no filtering).
Again, the issue is that when I hit home I get leak errors. Yet, after going home, I can go back to the app and find my list again - cursor fully intact.
