Matrixcursor with non-db content provider

Question

I have a content provider that returns a MatrixCursor for the query() method.

Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)
{
   MatrixCursor cursor = new MatrixCursor(new String[]{"a","b"});
   cursor.addRow(new Object[]{"a1","b1"});
   return cursor;
}

In the LoaderManager's onLoadFinished() callback method I use the cursor data to update a text view.

public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
    cursor.moveToFirst();
    String text = (String) textView.getText();
    while (!cursor.isAfterLast()) {
        text += cursor.getString(1);
        cursor.moveToNext();
    }
    textView.setText(text);

}

The question now is, how do I add a new row to the MatrixCursor that will notify the change to LoaderManager's callback methods promptly?

I hope, I have made the question clear. Thanks in advance.

Xenione · Answer 1 · 2015-12-21T11:01:23.267

I hope it's not too late or may be someone else could help.

The tricky thing here. It's you have to make a new cursor every time you query to the contentProvider for this reason I have my item list and every time I query content provider I build a new cursor with my backed item list that have new items.

Why I have to do tha? Otherwise you are going to get an exception becouse CursorLoader attempt to register an observer inside a cursor that already have one. Notice that the way to build new rows in a CursorMatrix is permitted in api level 19 and above, but you have alternative ways but involve more borring code.

public class MyContentProvider extends ContentProvider {

List<Item> items = new ArrayList<Item>();

@Override
public boolean onCreate() {
    // initial list of items
    items.add(new Item("Coffe", 3f));
    items.add(new Item("Coffe Latte", 3.5f));
    items.add(new Item("Macchiato", 4f));
    items.add(new Item("Frapuccion", 4.25f));
    items.add(new Item("Te", 3f));

    return true;
}


 @Override
public Cursor query(Uri uri, String[] projection, String selection,
        String[] selectionArgs, String sortOrder) {

    MatrixCursor cursor = new MatrixCursor(new String[] { "name", "price"});

    for (Item item : items) {
        RowBuilder builder = cursor.newRow();
        builder.add("name", item.name);
        builder.add("price", item.price);
    }

    cursor.setNotificationUri(getContext().getContentResolver(),uri);

    return cursor;
}


@Override
public Uri insert(Uri uri, ContentValues values) {
    items.add(new Item(values.getAsString("name"),values.getAsFloat("price")))

    //THE MAGIC COMES HERE !!!! when notify change and its observers registred make a requery so they are going to call query on the content provider and now we are going to get a new Cursor with the new item

    getContext().getContentResolver().notifyChange(uri, null);

    return uri;
}

How would this work for update and delete method if we want to make use of selection clause to update only one column and leave the others as is? — waseefakhtar, May 18 '18 at 11:46

Matrixcursor with non-db content provider

1 Answers1