how to update an Android ListActivity on changing data of the connected SimpleCursorAdapter

Question

I have the following code. What I want to achieve is to update the shown list when I click an entry so I can traverse through the list. I found the two uncommented ways to do it here on stackoverflow, but neither works. I also got the advice to create a new ListActivity on the data update, but that sounds like wasting resources?

EDIT: I found the solution myself. All you need to do is call "SimpleCursorAdapter.changeCursor(new Cursor);". No notifying, no things in UI-Thread or whatever.

import android.app.ListActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class MyActivity extends ListActivity {
    private DepartmentDbAdapter mDbHelper;
    private Cursor cursor;
    private String[] from = new String[] { DepartmentDbAdapter.KEY_NAME };
    private int[] to = new int[] { R.id.text1 };
    private SimpleCursorAdapter notes;

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.departments_list);
    mDbHelper = new DepartmentDbAdapter(this);
    mDbHelper.open();

    // Get all of the departments from the database and create the item list
    cursor = mDbHelper.fetchSubItemByParentId(1);
    this.startManagingCursor(cursor);

    // Now create an array adapter and set it to display using our row
    notes = new SimpleCursorAdapter(this, R.layout.department_row, cursor, from, to);
    this.setListAdapter(notes);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        // get new data and update the list
        this.updateData(safeLongToInt(id));
    }

    /**
     * update data for the list
     * 
     * @param int departmentId id of the parent department
     */
    private void updateData(int departmentId) {     
        // close the old one, get a new one
        cursor.close();
        cursor = mDbHelper.fetchSubItemByParentId(departmentId);

    // change the cursor of the adapter to the new one
    notes.changeCursor(cursor);
    }

    /**
     * safely convert long to in to save memory
     * 
     * @param long l the long variable
     * 
     * @return integer
     */
    public static int safeLongToInt(long l) {
    if (l < Integer.MIN_VALUE || l > Integer.MAX_VALUE) {
        throw new IllegalArgumentException
            (l + " cannot be cast to int without changing its value.");
    }
    return (int) l;
    }

}

Answer 1

You need to notify your ListVIew when your data get changed.

adapter.notifyDataSetChanged();

in your case.

notes.notifyDataSetChanged();

Hope this may help you...

Answer 2

First, every time you open a new cursor, close the previous one and manage the new one.

Second, you change your cursor, but how does your cursor adapter know that ? It doesn't. Either you create an adapter that can change its cursor or your create a new SimpleCursorAdapter around your new cursor and plug it to the list.

But you were right, you should not recreate the list widget.