How to dynamically update the choices in a SelectionCell using GWT?

Question

I am trying to have a table that displays data that the user inputs as well as edit the data. I have figured out how to do this with text (ie, they can edit the name of something in the table), but I cannot get it to work with selection cells.

It works correctly if the items in the selection cell are predefined, but I cannot dynamically update the items in the cell to include new things after I have created the cell.

To explain more, i have a "type" column. The user enters items into the table with a given type, but that can also add new types later. When they click on the item in the type column, I want the dropdown box to contain all the new types that they have entered, but I don't know how to accomplish this.

Here is the code I have so far (that doesn't update like I want it to). record.getTypeList() will contain additional entries after the user enters new types.

SelectionCell editTypeComboBox = new SelectionCell(record.getTypeList());

    Column<Assignment, String> typeColumn = new Column<Assignment, String>(editTypeComboBox) {
        @Override
        public String getValue(Assignment object) {
            return object.getType();
        }
    };
    typeColumn.setFieldUpdater(new FieldUpdater<Assignment, String>() {

        @Override
        public void update(int index, Assignment object, String value) {
            int row = index;
            String newType = value;
            record.editAssignType(row, newType);
            updateClassGradeLabel();
            log.info("Set type to "
                    + value);
            cellTable.redraw();
        }
    });

    cellTable.addColumn(typeColumn, "Type");

Edit: Thanks to Peter Knego foe helping me figure this out. Here is the modified DynamicSelectionCell class if anyone if interested:

/*
 * Copyright 2010 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.cell.client;

import com.google.gwt.core.client.GWT;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.dom.client.SelectElement;
import com.google.gwt.safehtml.client.SafeHtmlTemplates;
import com.google.gwt.safehtml.shared.SafeHtml;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * A {@link Cell} used to render a drop-down list.
 */
public class DynamicSelectionCell extends AbstractInputCell<String, String> {

  interface Template extends SafeHtmlTemplates {
    @Template("<option value=\"{0}\">{0}</option>")
    SafeHtml deselected(String option);

    @Template("<option value=\"{0}\" selected=\"selected\">{0}</option>")
    SafeHtml selected(String option);
  }

  private static Template template;

  private HashMap<String, Integer> indexForOption = new HashMap<String, Integer>();

  private final List<String> options;

  /**
   * Construct a new {@link SelectionCell} with the specified options.
   *
   * @param options the options in the cell
   */
  public DynamicSelectionCell(List<String> options) {
    super("change");
    if (template == null) {
      template = GWT.create(Template.class);
    }
    this.options = new ArrayList<String>(options);
    int index = 0;
    for (String option : options) {
      indexForOption.put(option, index++);
    }
  }

  public void addOption(String newOp){
      String option = new String(newOp);
      options.add(option);
      refreshIndexes();
  }

  public void removeOption(String op){
      String option = new String(op);
      options.remove(indexForOption.get(option));
      refreshIndexes();
  }

  private void refreshIndexes(){
        int index = 0;
        for (String option : options) {
          indexForOption.put(option, index++);
        }
  }

  @Override
  public void onBrowserEvent(Context context, Element parent, String value,
      NativeEvent event, ValueUpdater<String> valueUpdater) {
    super.onBrowserEvent(context, parent, value, event, valueUpdater);
    String type = event.getType();
    if ("change".equals(type)) {
      Object key = context.getKey();
      SelectElement select = parent.getFirstChild().cast();
      String newValue = options.get(select.getSelectedIndex());
      setViewData(key, newValue);
      finishEditing(parent, newValue, key, valueUpdater);
      if (valueUpdater != null) {
        valueUpdater.update(newValue);
      }
    }
  }

  @Override
  public void render(Context context, String value, SafeHtmlBuilder sb) {
    // Get the view data.
    Object key = context.getKey();
    String viewData = getViewData(key);
    if (viewData != null && viewData.equals(value)) {
      clearViewData(key);
      viewData = null;
    }

    int selectedIndex = getSelectedIndex(viewData == null ? value : viewData);
    sb.appendHtmlConstant("<select tabindex=\"-1\">");
    int index = 0;
    for (String option : options) {
      if (index++ == selectedIndex) {
        sb.append(template.selected(option));
      } else {
        sb.append(template.deselected(option));
      }
    }
    sb.appendHtmlConstant("</select>");
  }

  private int getSelectedIndex(String value) {
    Integer index = indexForOption.get(value);
    if (index == null) {
      return -1;
    }
    return index.intValue();
  }
}

Answer 1

Unfortunately SelectionCell stores options in a private List and there are no methods to manipulate this after you have set them in constructor.

Fortunately, SelectionCell is a fairly simple class. Just make your own (renamed) copy and add addOption(..)/removeOption(..) methods to manipulate List<String> options.