Cursor Utils

CURSORS:THE GOOD PARTS

▸ Fast▸ Flexible

▸ Good for large datasets

CURSORS:THE ROUGH POINTS

▸ No type safety▸ Lots of code duplication▸ No easy iteration mechanism

Cursor UtilsTO THE RESCUE!

IterableCursor<T>extends Iterable<T>, Cursor

// Public API:

public T peek();public T nextDocument();public T previousDocument();public Iterator<T> iterator();

IterableCursor<T>extends Iterable<T>, Cursor

// Public API:

public T peek();// public T nextDocument();// public T previousDocument(); // @see CursorUtils.java helpers// public Iterator<T> iterator();

That's it.

public class User { public User(String name, String bio) { /* ... */ }}

public class UserCursor extends IterableCursorWrapper<User> {

public UserCursor(Cursor c) { super(c); }

public User peek() { String name = getStringHelper(COLUMN_USER_NAME, "Default Name"); String bio = getLongHelper(COLUMN_USER_BIO, "No bio yet"); return new User(name, bio); }

}

IterableCursorWrapper<T> Helper Methods

getString(columnIndex) vs. getStringHelper(columnName, defaultValue)getDouble(columnIndex) vs. getDoubleHelper(columnName, defaultValue)// ...get*(columnIndex) vs. get*Helper(columnName, defaultValue)

IterableCursorWrapper<T> Helper Methods

getString(columnIndex) vs. getStringHelper(columnName, defaultValue)getDouble(columnIndex) vs. getDoubleHelper(columnName, defaultValue)// ...get*(columnIndex) vs. get*Helper(columnName, defaultValue)

Effective Java, Item 79: Use these helper methods judiciously.

IterableCursorWrapper<T> Helper Methods

getString(columnIndex) vs. getStringHelper(columnName, defaultValue)getDouble(columnIndex) vs. getDoubleHelper(columnName, defaultValue)// ...get*(columnIndex) vs. get*Helper(columnName, defaultValue)

Effective Java, Item 79: Use these helper methods judiciously.They're convenient, but definitely slower.

Back to code

public class MyDatabase extends SQLiteOpenHelper {

// ...

public IterableCursor<User> queryAllUsers() { Cursor cursor = getReadableDatabase().query(TABLE_USERS, /* ... */); return new UserCursor(cursor); }

}

IterableCursor<User> users = myDb.queryAllUsers();for (User user : users) { if (user.isMyBestFriend()) giveSomeCake(user);}users.close();

IterableCursorAdapter<T>Here's where the magic happens

IterableCursorAdapter<T>

public abstract View newView(Context context, T t, ViewGroup parent);public abstract void bindView(View view, Context context, T t);

IterableCursorAdapter<T>

public abstract View newView(Context context, T t, ViewGroup parent);public abstract void bindView(View view, Context context, T t);

"It's like ArrayAdapter<T> + CursorAdapter!"

— Our Intern

CursorListIterableCursor<T> + List<T>

CursorListIterableCursor<T> + List<T>(Cursor + Iterable<T>) + List<T>

CursorList

Useful if you want to only have one instance created per row.

(IterableCursorWrapper<T> by default creates a new instance on every .peek())

CursorList

Great for filtering data sets:

@Overridepublic IterableCursor<User> runQueryOnBackgroundThread(CharSequence constraint) { CursorList<User> filtered = new CursorList<User>(); for (User user : getCursor()) { if (user.nameMatches(constraint)) { filtered.add(user); } } return filtered;}

For the RxJava Folks:

Observable<IterableCursor<Pojo>> observable = // ...observable .map(cursor -> new CursorList(cursor)) .subscribeOn(Schedulers.io) .observeOn(AndroidSchedulers.mainThread())

For the RxJava Folks:

Observable<IterableCursor<Pojo>> pojos = // ... Observable.from(pojos) .forEach(pojo -> /* ... */);

Ron Shapiro ron@venmo.com

@rdshapiro !

venmo.com/ronshapiro

Questions?

github.com/venmo/cursor-utils compile ‘com.venmo.cursor:library:0.2’

!

Contribute!

Where can I get the new hotness?