Question

I’m trying to populate a ListView with data from a query using a CursorLoader. I’m new to CursorLoaders and I’m using code I purloined from Beginning Android 4 Application Development. As you can see, I’m getting data from an Intent. The data in the Intent is what I want; I’ve verified that in the debugger. However, when I query my database, nothing displays in the ListView. Can anyone help?

public class MyList extends ListActivity implements LoaderManager.LoaderCallbacks<Cursor> {

private static final String TABLE_BASEPATH = "tbl";
private static final String AUTHORITY = "SQLData";
public static final Uri MY_URI = Uri.parse("content://" + AUTHORITY + "/" + TABLE_BASEPATH);    

@SuppressWarnings("deprecation")
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Intent myData = getIntent();
    Bundle info = myData.getExtras();

    if (info != null){
        Cursor c;
        String[] dataColumns = { "mycolumn" };
        String selection = "level = '" + info.getString("Level") + "'";

        if (android.os.Build.VERSION.SDK_INT < 11)
            c = managedQuery(MY_URI, dataColumns, selection, null, "ORDER BY mycolumn");
        else
        {
            CursorLoader cursorloader = new CursorLoader(this, MY_URI, dataColumns, selection, null, "ORDER BY mycolumn");
            c = cursorloader.loadInBackground();
        }

        int[] viewIDs = { R.id.mylist1 };
        SimpleCursorAdapter adapter;

        if (android.os.Build.VERSION.SDK_INT < 11)
            adapter = new SimpleCursorAdapter(this, R.layout.mylist, c, dataColumns, viewIDs);
        else
            adapter = new SimpleCursorAdapter(this, R.layout.mylist, c, dataColumns, viewIDs, CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);

        this.setListAdapter(adapter);
    }
}

public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    return new CursorLoader(this, MY_URI,
            PROJECTION, null, null, null);  
}

public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
    switch (loader.getId()) {
      case LOADER_ID:
        mAdapter.swapCursor(cursor);
        break;
    }

}

public void onLoaderReset(Loader<Cursor> loader) {
    mAdapter.swapCursor(null);

}

It doesn’t matter if I’m using the cursor or the CursorLoader. If my version is < 11 (cursor), I get no data; if it’s > 11 (CursorLoader) I still get no data.

Answer 1

You need to put in the id column in the projection when working with ContentProviders, otherwise they “won’t work”. Which I think you are doing > api level 11…

String[] dataColumns = { "mycolumn" };

The above code should include the id field. If the id field is “_id” (like Sams answer):

String[] dataColumns = { "mycolumn", "_id" };