Android CursorLoader and LoaderManager Error

Question

I am trying to implement a CursorLoader and LoaderManager on a min API of 10.

However, I keep getting an IllegalArgument Exception on Line 63 of AsyncTaskLoader.class (The source Code of the AsyncTaskLoader.class where the exception is happening is Below and at this link.

/* Runs on the UI thread */
@Override
protected void onPostExecute(D data) {
    if (DEBUG) Log.v(TAG, this + " onPostExecute");
    try {
        AsyncTaskLoader.this.dispatchOnLoadComplete(this, data);
    } finally {
        done.countDown();
    }
}

Below is the stack upon the error:

AsyncTaskLoader$LoadTask.onPostExecute(Object) line: 63 
AsyncTaskLoader$LoadTask(ModernAsyncTask).finish(Object) line: 461  
ModernAsyncTask.access$500(ModernAsyncTask, Object) line: 47    
ModernAsyncTask$InternalHandler.handleMessage(Message) line: 474    
ModernAsyncTask$InternalHandler(Handler).dispatchMessage(Message) line: 99  
Looper.loop() line: 137 
ActivityThread.main(String[]) line: 4424    
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
Method.invoke(Object, Object...) line: 511  
ZygoteInit$MethodAndArgsCaller.run() line: 784  
ZygoteInit.main(String[]) line: 551 
NativeStart.main(String[]) line: not available [native method]  

I tested my content provider and I validated that the query method returns a valid cursor from my Sqlite Database. Below is the source code of my activity that I am trying to implement the CursorLoader and LoaderManager:

import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v4.widget.SimpleCursorAdapter;
import android.widget.ListView;

public class Screen1_MainData extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor> {

    SimpleCursorAdapter adapter;
    ListView lv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.screen1_maindata);
        initLoader();
    }

    void initLoader() {
        String[] uiBindFrom = { Useful_Info_TableMetaData.USEFUL_INFO_COLUMN_NAME };
        int[] uiBindTo = { R.id.name };
        lv = (ListView) findViewById(R.id.screen1_MainListView);
        getSupportLoaderManager().initLoader(0, null, this);

        adapter = new SimpleCursorAdapter(this, R.layout.row, null, uiBindFrom,
                uiBindTo, 0);
        lv.setAdapter(adapter);    
    }

@Override
public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) {

    String[] projection = { Useful_Info_TableMetaData.USEFUL_INFO_COLUMN_NAME };

    return new CursorLoader(
            this, // The Activity context
            Useful_Info_TableMetaData.CONTENT_URI, projection, null, null,
            null);
}

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

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

Does anyone see something here that I am doing wrong?

Thanks.

---

The app seems to make it to

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

and then it throws the exception there.

Below is the logcat:

08-03 23:33:20.736: E/AndroidRuntime(17256): FATAL EXCEPTION: main 
08-03 23:33:20.736: E/AndroidRuntime(17256): java.lang.IllegalArgumentException: column '_id' does not exist 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:267) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.database.CursorWrapper.getColumnIndexOrThrow(CursorWrapper.java:78) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.support.v4.widget.CursorAdapter.swapCursor(CursorAdapter.java:344) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.support.v4.widget.SimpleCursorAdapter.swapCursor(SimpleCursorAdapter.java:326) 

Answer 1

Try moving initLoader after your call to lv.setAdapter. This will ensure that onLoadFinished (and thus adapter.swapCursor(data)) will be called after the SimpleCursorAdapter has been associated with the ListView .

Also, make sure your database has a column named _id for your primary key, as the CursorAdapter won't work otherwise. _id needs to be returned as a part of the results from the CursorLoader's. Otherwise an exception will be thrown.