Question

In my android application I would like to display items in a list. For this I’m using listView. Because the list items consist of a text (name) and an editText (quantity) I’m using custom ArraryAdapter. I’m using editText because I would like to allow the user to modify the quantity. When the user has stopped editing, I would like to store the new value, so I have added an onTextChanged event to the editTexts.

I created a class for the items (that I’m displaying in the list). It’s very simple, it has only name and quantity:

public class Foo {
    final String name;
    int quantity;

    public Foo (String name, int quantity) {
        this.name = name;
        this.quantity = quantity;
    }

    // for debug message
    @Override
    public String toString () {
        return "name: " + this.name+ " quantity: " + this.quantity;
    }
}

In the main activity’s onCreate method I create a list of Foo elements and I use an own Adapter for them to put in the list:

public class MainActivity extends Activity {
    ListView list;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        list = (ListView) findViewById (R.id.list);
        List<Foo> elements = new ArrayList<Foo> ();
        elements.add(new Foo ("foo", 1));
        elements.add(new Foo ("bar", 2));
        elements.add(new Foo ("baz", 3));
        elements.add(new Foo ("foo2", 4));
        elements.add(new Foo ("bar2", 5));
        elements.add(new Foo ("baz2", 6));

        FooAdapter adapter = new FooAdapter (this, R.layout.foo_elements, elements);
        //where foo_elements contains a horizontal LinearLayout and in it
        //there's a TextView and an EditText
        list.setAdapter(adapter);
    }

So my adapter is the following (I found the holder pattern here: http://www.vogella.com/articles/AndroidListView/article.html#adapterperformance_hoder):

public class FooAdapter extends ArrayAdapter<Foo> {
    Context context;
    int layoutResourceId;
    List<Foo> elements;

    public FooAdapter (Context context, int layoutResourceId, List<Foo> elements) {
        super (context, layoutResourceId, elements);
        this.context = context;
        this.layoutResourceId = layoutResourceId;
        this.elements = elements;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row = convertView;
        Holder holder = null;

        final Foo item = elements.get(position);

        if (row == null) {
            LayoutInflater inflater = ((Activity)context).getLayoutInflater ();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new Holder ();
            holder.name = (TextView) row.findViewById (R.id.name);
            holder.quantity = (EditText) row.findViewById(R.id.quantity);

            holder.quantity.addTextChangedListener(new TextWatcher() {

                @Override
                public void onTextChanged(CharSequence s, int start, int before, int count) {
                    // TODO Auto-generated method stub
                }

                @Override
                public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                    // TODO Auto-generated method stub
                }

                @Override
                public void afterTextChanged(Editable s) {
                    Log.d("textchanged", "text has changed");
                    Log.d ("new text", s.toString());
                    item.quantity = Integer.parseInt(s.toString());
                }
            });

            row.setTag(holder);
        }
        else {
            holder = (Holder) row.getTag();
        }

        holder.name.setText (item.name);
        holder.quantity.setText (String.valueOf(item.quantity));

        return row;
    }

    class Holder {
        TextView name;
        EditText quantity;
    }
}

As you can see I used TextWatcher for listening to the textchanged event and in afterTextChanged function I would like to set the new quantity to the Foo object.

I put some debug messages to see what’s happening there and I added a button to print the Foo objects. After starting my application the output is this:

textchanged      text has changed
new text         1
textchanged      text has changed
new text         2
textchanged      text has changed
new text         3
textchanged      text has changed
new text         4
textchanged      text has changed
new text         5
textchanged      text has changed
new text         6
textchanged      text has changed
new text         6
textchanged      text has changed
new text         2
textchanged      text has changed
new text         3
textchanged      text has changed
new text         4
textchanged      text has changed
new text         5
textchanged      text has changed
new text         6

So after launching the program the quantities are:

name: foo quantity: 6 //instead of name: foo quantity: 1
name: bar quantity: 2
name: baz quantity: 3
name: foo2 quantity: 4
name: bar2 quantity: 5
name: baz2 quantity: 6

If I modify the last element then it changes the first element too:

name: foo quantity: 62 //instead of name: foo quantity: 1
name: bar quantity: 2
name: baz quantity: 3
name: foo2 quantity: 4
name: bar2 quantity: 5
name: baz2 quantity: 62

I’m new to Android (even Java) and I didn’t find my fault. Do you have any idea? And why so many textchanged events? How does it work? Do I use the listView wrongly? Thanks in advance.

Answer 1

I think your problem it here.

item.quantity = Integer.parseInt(s.toString());

item variable can be not that you want there. See this post: Android SimpleAdapter wrong data-item gets associated with a list row it describes that getView can be called not one time and view can be reused. You successfully impliment it with setting name and value here:

holder.name.setText (item.name);
holder.quantity.setText (String.valueOf(item.quantity));

But not with EditText. Set tag to your edit view, or retrieve item in an other way to correct it.

Hope it will help.