无法从具有3行，3列的CursorWindow中读取第0行，第3列

Question

I know this question has been asked before, but I can't seem to find the answer in the other posts about this. I have the error "Failed to read row 0, column 3 from a CursorWindow which has 3 rows, 3 columns" and with that "Couldn't read row 0, col 3 from CursorWindow.". I'm trying to make a to-do list for Android. I'm not sure why this error is coming, cause I know that my DB has 4 columns (0 to 3) like the error says I'm trying to read row 0 column 3 (which should be possible, since there are 3 columns) and still it gives me the error. Below is the code (it's separated in files, I'll put the file where the error occurs first (btw, it on: String taskReminder = cursor.getString(reminderColumnIndex);

Hope you guys can help me out, and sorry for asking a question which was asked before, but I really couldn't find the answer in the other posts.

Edited: I think this is the code you need:

CatalogActivity.java

some imports...
public class CatalogActivity extends AppCompatActivity implements
        LoaderManager.LoaderCallbacks<Cursor> {

    private static final int TASK_LOADER = 0;

    CursorAdapter mCursorAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_catalog);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
                startActivity(intent);
            }
        });

        ListView taskListView = findViewById(R.id.list);

        View emptyView = findViewById(R.id.empty_view);
        taskListView.setEmptyView(emptyView);

        mCursorAdapter = new CursorAdapter(this, null);
        taskListView.setAdapter(mCursorAdapter);

        taskListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);

                Uri currentTaskUri = ContentUris.withAppendedId(Entry.CONTENT_URI, id);

                intent.setData(currentTaskUri);

                startActivity(intent);
            }
        });

        getLoaderManager().initLoader(TASK_LOADER, null, this);
    }

    private void deleteAllTasks() {
        int rowsDeleted = getContentResolver().delete(Entry.CONTENT_URI, null, null);
        Log.v("CatalogActivity", rowsDeleted + " rows deleted from task database");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_catalog, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_insert_dummy_data:
                insertTask();
                return true;
            case R.id.action_delete_all_entries:
                deleteAllTasks();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
        String[] projection = {
                Entry._ID,
                Entry.COLUMN_TASK_NAME,
                String.valueOf(Entry.COLUMN_TASK_COMPLETED)};

        return new CursorLoader(this,   // Parent activity context
                Entry.CONTENT_URI,      // Provider content URI to query
                projection,             // Columns to include in the resulting Cursor
                null,                   // No selection clause
                null,                   // No selection arguments
                null);                  // Default sort order
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        mCursorAdapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        mCursorAdapter.swapCursor(null);
    }
}

Also, I think, I found the solution. Correct me if I'm wrong: in the String[] projection, I only have, apart from the ID, the name and if it's completed. I'm guessing here needs to be the reminderdate as well?

Edited: Yes, solved my own problem. I put the reminderdata in the String[] projection and now it works. I couldn't have done it without you guys (you pointed me in the right direction), so thank you very mutch. You are the best!

Answer 1

Column indexing is zero-based. A Cursor with 3 columns has values at indexes 0, 1 and 2. That would explain the exception as listed in your question title.

The code you posted does not seem to be the code that produces that exception. You obtain column index with getColumnIndex() which returns -1 for columns that are not in the cursor. It never returns an index that is not in the cursor.