android - Refreshing checkbox state in a listview

Question

I have list view with custom row layout (list_row.xml) that contains CheckBox element:

<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent"
    android:orientation="horizontal"
    android:weightSum="1.0">
    <TableRow>
        <TextView android:id="@+id/name"
            android:layout_weight=".85"
            android:layout_width="0dip"
            android:layout_height="wrap_content"
            android:text="sample"
            android:textSize="24sp">
        </TextView>
        <CheckBox android:id="@+id/enabled"
            android:layout_weight=".15"
            android:layout_width="0dip"
            android:layout_height="wrap_content" 
            android:focusable="false">
        </CheckBox>
    </TableRow>
</TableLayout>

In my list activity I've got ListRowAdapter:

private static class ListRowAdapter extends ArrayAdapter<ListRow> implements
        CompoundButton.OnCheckedChangeListener {

    private List<ListRow> items;
    private LayoutInflater vi;
    private SparseBooleanArray mCheckStates;

    public ListRowAdapter(Context context, int textViewResourceId,
            List<ListRow> objects) {
        super(context, textViewResourceId, objects);
        this.items = objects;
        this.vi = LayoutInflater.from(context);
        this.mCheckStates = new SparseBooleanArray(objects.size());
        for(int i=0;i<mCheckStates.size();i++){
            mCheckStates.put(i,items.get(i).isEnabled());
        }
        Log.i("VIEW", "constructor");
    }

    public boolean isChecked(int position) {
        return mCheckStates.get(position, false);
    }

    public void setChecked(int position, boolean isChecked) {
        mCheckStates.put(position, isChecked);
        items.get(position).setEnabled(isChecked);
        notifyDataSetChanged();
    }

    public void toggle(int position) {
        setChecked(position, !isChecked(position));
    }

    public void onCheckedChanged(CompoundButton buttonView,
            boolean isChecked) {
        ListRow r = (ListRow) buttonView.getTag();
        r.setEnabled(isChecked);
        mCheckStates.put(items.indexOf(r), isChecked);
        Toast.makeText(getContext(), "row " + r.getName() + " changed to "+isChecked, Toast.LENGTH_SHORT).show();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            Log.i("VIEW", "init holder");
            convertView = vi.inflate(R.layout.list_row, null);
            holder = new ViewHolder();
            holder.name = (TextView) convertView.findViewById(R.id.name);
            holder.enabled = (CheckBox) convertView
                    .findViewById(R.id.enabled);
            convertView.setTag(holder);
        } else {
            Log.i("VIEW", "using holder");
            holder = (ViewHolder) convertView.getTag();
        }
        ListRow row = items.get(position);
        if (row != null) {
            holder.name.setText(row.getName());
            holder.enabled.setTag(row);
            holder.enabled.setChecked(mCheckStates.get(position, false));           holder.enabled.setOnCheckedChangeListener(this);
        }
        return convertView;
    }

    static class ViewHolder {
        TextView name;
        CheckBox enabled;
    }

}

In my Activity (that extends ListActivity) I do the following:

private static List<ListRow> rows;
private ListRowAdapter lra;

... and then

getListView().setItemsCanFocus(false);
getListView().setTextFilterEnabled(true);
rows = initRows();
lra = new ListRowAdapter(this, R.layout.list_row, rows);
setListAdapter(lra);

and that works fine while scrolling. But if I don't use mCheckStates array it fails! I just can't understand why. I have items array as a member of my Activity class and it contains all the states of checkboxes! I update it in onCheckedChanged() method like I update mCheckState. So the following code has to work:

public boolean isChecked(int position) {
    return items.get(position).isEnebled();
}

public void setChecked(int position, boolean isChecked) {
    items.get(position).setEnabled(isChecked);
    notifyDataSetChanged();
}

public void toggle(int position) {
    setChecked(position, !isChecked(position));
}

public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    ListRow r = (ListRow) buttonView.getTag();
    r.setEnabled(isChecked);
    Toast.makeText(getContext(), "row " + r.getName() + " changed to "+isChecked, Toast.LENGTH_SHORT).show();
}

and in getView() method:

holder.enabled.setTag(row);holder.enabled.setChecked(row.isEnabled());

But it doesn't. It loses checkbox states while scrolling and I don't know why.

Answer 1

I'm not sure I followed everything you said there, but keep in mind that ListView recycles views as you scroll. This means that you cannot assume that a view will be in any default state at the start of getView. This is probably why it doesn't work when you stop resetting the checkbox to the correct state every time you get a new view.

That said, did you consider using ListViews built in checkbox tool? Set its choice mode to CHOICE_MODE_MULTIPLE and use one of their provided layouts, like android.R.layout.simple_list_item_multiple_choice.