Hello!
I want to write a ListAdapter to serve data from a database that look like
this:
CREATE TABLE notes (_id integer primary key,
content text);
CREATE TABLE tags (_id integer primary key,
name text,
pos integer
noteid integer,
foreign key(noteid) references notes(_id));
I use this database to store notes and their associated tags. One
requirement of the ListAdapter is that it must be able to update the
ListView contents if the underlying data changes. I can query all the notes
in the database with this query:
select notes._id as id, notes.content, tags.pos, tags.name
from notes left join tags on id = tags.noteid
order by id, tags.pos;
Which will give me results looking like this (null values shown for
clarity):
0|foo bar baz|0|x
1|hello world|null|null
2|one more nn|0|yy
2|one more nn|1|y
As you can see, note with mote than one tag will be located on more than one
row in the result. This means that I can't look at the cursor size to
determine the number of notes, I need to traverse the entire Cursor to get a
count. I don't want to do that.
The solution I have come up with so far is to use two cursors: one with the
query mentioned above and one with a query containing the number of rows in
the notes table (select count(*) from notes;). In the constructor I call
intializeCursorsI():
private void initializeCursors() {
notesCursor.moveToFirst();
countCursor.moveToFirst();
count = countCursor.getInt(0);
}
I have implemented getItem() like this:
public Note getItem(int position) {
if (position < notes.size()) { // notes is a List of notes that we
have already read.
return notes.get(position);
}
int cursorPosition = notes.size();
while (cursorPosition <= position) {
Note note = NotesDb.noteFrom(notesCursor); // Creates a note by
reading the correct number of rows.
notes.add(note);
++cursorPosition;
}
return notes.get(position);
}
The adapter assumes that the cursors are being managed by some activity that
has called startManagingCursor() on them.
So far so good, I guess. The problem is now how to handle the cursor being
requeried. Since I have two cursors I need to register listeners for both of
them and when I have received onChange() for both of them I can
initializeCursors() and notify any listeners registered to my ListAdapter of
a change in the its data.
This is the best I have so far. I want to check the sanity of this approach
with this group. :-) Is this way to complicated? Perhaps I have missed some
part of the API that solves this nicely for me?
Thanks in advance!
:.:: mattias
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