Develop Reference

When to close Cursor used in SimpleCursorAdapter

I'm using a SimpleCursorAdapter to display results in a ListView but since I've got to query my database lots of times during a search (using the SearchView widget) it worries me that the cursor might be left opened.
This is how I query my database and show the results in a ListView:
class SearchCustomers extends AsyncTask<String,Void,Cursor>{
#Override
protected Cursor doInBackground(String... params) {
//get the query
String query=params[0].toLowerCase(Locale.getDefault());
Cursor cursor=mDB.searchCustomersByName((query != null ? query : "####"));
return cursor;
}
#Override
protected void onPostExecute(Cursor result) {
if (result != null) {
String[] from = new String[] { QuickOrderDB.ID,
QuickOrderDB.NAME,
QuickOrderDB.ADDRESS,
QuickOrderDB.PHONE_NUMBER };
int[] to = new int[] { R.id.customerIDTextView,
R.id.customerNameTextView,R.id.customerAddressTextView ,
R.id.customerPhoneTextView };
SimpleCursorAdapter cursorAdapter = new SimpleCursorAdapter(SearchCustomersActivity.this,
R.layout.results_customer_item, result, from, to);
mResultsListView.setAdapter(cursorAdapter);
}
}
}
I have tried many things to close the cursor, but even If I close it after mResultsListView.setAdapter(cursorAdapter); the result is always the same: an empty ListView.
I've already seen a couple of questions in which it is mentioned that the cursor will be closed automatically, but I want to make sure this is true.
Is there any official documentation about this? Does the SimpleCursorAdapter really close the cursor automatically??
Thanks in advance.

You need to close your cursor once you are done with it. Closing it after setAdapter() call would prevent the adapter from accessing the data. Hence a better place to close the cursor would be during current activities tear down life cycle stages such as onPause() or onStop(). (onDestroy() should not be used as Android run-time does not guarantee calling it. I think on latest version onStop() is guaranteed)
I don't think SimpleCursorAdapter adapter automatically closes the cursor automatically. The official document mentions that changeCursor() automatically closes the old cursor, so another option could be to change your cursor after search.
http://developer.android.com/reference/android/widget/CursorAdapter.html#changeCursor(android.database.Cursor)

It's better if you get the Cursor using a CursorLoader instead of an AsyncTask.
The Loaders are synched to the Activity/Fragment lifecycle via the LoaderManager, and the system will close the Cursor provided by the CursorLoader automatically for you when it's needed.

You should close the cursor in your fragment or activity's onPause() callback. After the activity is paused it's possible that older Android systems will delete the app to free memory.
This implies that you need to reestablish the cursor in the corresponding onResume() callback.

Don't create a variable for the cursor, just add the db query directly into the constructor as the argument c, db.query() or a method that holds the desired query), this seems to work.
SimpleCursorAdapter (Context context,
int layout,
Cursor c,
String[] from,
int[] to,
int flags)

Android: how to use CursorAdapter?

I have a database, a ListView, and a CustomCursorAdapter that extends CursorAdapter. A menu button adds an item to the database. I want the ListView to update and show this change. Normally it doesn't show this new item until i go to the homescreen and reopen the application.
I did eventually get it to work by calling cursor.requery() or mCustomCursorAdapter.changeCursor(newCursor) whenever I added a new item, but when I set autoRequery to false in the CursorAdapter constructor, it worked just the same. Why does it update correctly when autoRequery is set to false?
Am I using CursorAdapter correctly? What is the standard way of keeping the list updated with the database? And what does autoRequery do?

The idiomatic and imho correct way to automatically update Cursors is to call Cursor#setNotificationUri when they are created and before they are handed off to whatever requested them. Then call ContentResolver#notifyChange when anything in that Cursor's Uri's namespace changes.
For example, suppose you were creating a simple mail application and you wanted to update when new mail arrived but also provide various views on the mail. I'd have some basic Uri's defined.
content://org.example/all_mail
content://org.example/labels
content://org.example/messages
Now, say I wanted to get a cursor that gave me all mail and be updated when new mail arrives:
Cursor c;
//code to get data
c.setNotificationUri(getContentResolver(), Uri.parse("content://org.example/all_mail");
Now new mail arrives so I notify:
//Do stuff to store in database
getContentResolver().notifyChange(Uri.parse("content://org.example/all_mail", null);
I should also notify all the Cursors that selected for labels this new message met
for(String label : message.getLabels() {
getContentResolver().notifyChange(Uri.parse("content://org.example/lables/" + label, null);
}
And also, maybe a cursor is viewing that one specific message so notify them as well:
getContentResolver().notifyChange(Uri.parse("content://org.example/messages/" + message.getMessageId(), null);
The getContentResolver() calls happen where the data is accessed. So if it's in a Service or ContentProvider that is where you setNotificationUri and notifyChange. You should not be doing that from where the data is accessed, e.g., an Activity.
AlarmProvider is a simple ContentProvider that uses this method to update Cursors.

I created next method for ListView updating:
/**
* Method of refreshing Cursor, Adapter and ListView after database
* changing
*/
public void refreshListView() {
databaseCursor = db.getReadableDatabase().query(
CurrentTableName,
null,
null,
null,
null,
null,
"title"+SortingOrder);
databaseListAdapter = new DomainAdapter(this,
android.R.layout.simple_list_item_2,
databaseCursor,
new String[] {"title", "description"},
new int[] { android.R.id.text1, android.R.id.text2 });
databaseListAdapter.notifyDataSetChanged();
DomainView.setAdapter(databaseListAdapter);
}
end calls it each time after some changing in database

Dynamically update autocomplete box in Android?

I will like to know if we can continuously call some service for fetching results and displaying in Autocomplete list.
I have one screen with the text box and when user starts entering in that textbox the autocomplete should get filled with the data. The data will not be hardcoded and will be fetched through http connection. I think I need to call http connection in onTextChanged method of Edittext but is that the perfect solution.
Moreover, should this type of implementation done in mobile application. Since, this feature is web based. Can this be done in mobile application too?
Is this feasible?

Write a custom SimpleCursorAdapter. Now associate this adapter to your EditText. Here is the code to construct a Cursor object and return it:
public class ValueCursorAdapter extends SimpleCursorAdapter implements Filterable
{
...
// overrise the newView() to associate mCursor[1] and mCursor[2] to relevant views within
...
#Override
public Cursor runQueryOnBackgroundThread(CharSequence constraint)
{
MatrixCursor mCursor = new MatrixCursor(new String[] { "_id", "uri", "label" });
.. // result = ??
while (result.hasNext())
{
mCursor.addRow(new Object[] { count, "uri", "title"});
count++;
}
return mCursor;
}
}
Here is an example for Customizing Cursor Adapter. You might need to customize it to fit your requirements.

Android: Filtering a SimpleCursorAdapter ListView

Right now, I'm running into issues trying to implement a FilterQueryProvider in my custom SimpleCursorAdapter, since I'm unsure of what to do in the FilterQueryProvider's runQuery function.
In other words, since the query that comprises my ListView basically gets the rowID, name, and a third column from my databases's table, I want to be able to filter the cursor based on the partial value of the name column.
However, I am uncertain of whether I can do this directly from runQuery without expanding my DB class since I want to filter the existing cursor, or will I have to create a new query function in my DB class that partially searches my name column, and if so, how would I go about creating the query statement while using the CharSequence constraint argument in runQuery?
I am also concerned about the performance issues associated with trying to run multiple queries based on partial text since the DB table in question has about 1300-1400 rows. In other words, would I run into a bottleneck trying to filter the cursor?

You need to run a query that will return a new filtered cursor:
public class MyActivity extends ListActivity implements FilterQueryProvider {
private Cursor cursor;
#Override
public Cursor runQuery(CharSequence constraint) {
if(cursor != null) {
cursor.close();
}
cursor = somehowGetAFilteredCursorFor(constraint);
startManagingCursor(cursor);
return cursor;
}
}

Android SimpleCursorAdapter doesn't update when database changes

I have an Android ListActivity that is backed by a database Cursor through a SimpleCursorAdapter.
When the items are clicked, a flag field in the coresponding row in the database is toggled and the view in the list needs to be updated.
The problem is, when the view that's updated goes off screen and is recycled, the old value is displayed on the view when it returns into view. The same thing happens whenever thr list is redrawb (orientation changes, etc).
I use notifydatasetchanged() to refresh the cursor adapter but it seems ineffective.
How should I be updating the database so the cursor is updated as well?

Call requery() on the Cursor when you change data in the database that you want reflected in that Cursor (or things the Cursor populates, like a ListView via a CursorAdapter).
A Cursor is akin to an ODBC client-side cursor -- it holds all of the data represented by the query result. Hence, just because you change the data in the database, the Cursor will not know about those changes unless you refresh it via requery().
UPDATE: This whole question and set of answers should be deleted due to old age, but that's apparently impossible. Anyone seeking Android answers should bear in mind that the Android is a swiftly-moving target, and answers from 2009 are typically worse than are newer answers.
The current solution is to obtain a fresh Cursor and use either changeCursor() or swapCursor() on the CursorAdapter to affect a data change.

requery is now deprecated. from the documentation:
This method is deprecated.
Don't use this. Just request a new cursor, so you can do this asynchronously and update your list view once the new cursor comes back.
after obtaining a new cursor one can use theadapter.changeCursor(cursor). this should update the view.

In case of using loader and automagically generated cursor you can call:
getLoaderManager().restartLoader(0, null, this);
in your activity, just after changing something on a DB, to regenerate new cursor.
Don't forget to also have event handlers defined:
#Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
CursorLoader cursorLoader =
new CursorLoader(this,
YOUR_URI,
YOUR_PROJECTION, null, null, null);
return cursorLoader;
}
#Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
adapter.swapCursor(data);
}
#Override
public void onLoaderReset(Loader<Cursor> loader) {
adapter.swapCursor(null);
}

I am not clear if you set the autoRequery property of CursorAdapter to true.
The adapter will check the autoRequery property; if it is false, then the cursor will not be changed.

requery() is already deprecated, just implement the simple updateUI() method like this in your CursorAdapter's child class and call it after data updates:
private void updateUI(){
swapCursor(dbHelper.getCursor());
notifyDataSetChanged();
}

It's easy.
private Db mDbAdapter;
private Cursor mCursor;
private SimpleCursorAdapter mCursorAd;
.....................................
//After removing the item from the DB, use this
.....................................
mCursor = mDbAdapter.getAllItems();
mCursorAd.swapCursor(mCursor);
Or use CursorLoader...