title: How to dynamically update the choices in a SelectionCell using GWT?
body: <p>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.  </p>
  
  <p>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. </p>
  
  <p>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. </p>
  
  <p>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. </p>
  
  <pre><code>SelectionCell editTypeComboBox = new SelectionCell(record.getTypeList());
  
      Column&lt;Assignment, String&gt; typeColumn = new Column&lt;Assignment, String&gt;(editTypeComboBox) {
          @Override
          public String getValue(Assignment object) {
              return object.getType();
          }
      };
      typeColumn.setFieldUpdater(new FieldUpdater&lt;Assignment, String&gt;() {
  
          @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");
  </code></pre>
  
  <p><b>Edit:</b>
  Thanks to Peter Knego foe helping me figure this out. Here is the modified DynamicSelectionCell class if anyone if interested:</p>
  
  <pre><code>/*
   * 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&lt;String, String&gt; {
  
    interface Template extends SafeHtmlTemplates {
      @Template("&lt;option value=\"{0}\"&gt;{0}&lt;/option&gt;")
      SafeHtml deselected(String option);
  
      @Template("&lt;option value=\"{0}\" selected=\"selected\"&gt;{0}&lt;/option&gt;")
      SafeHtml selected(String option);
    }
  
    private static Template template;
  
    private HashMap&lt;String, Integer&gt; indexForOption = new HashMap&lt;String, Integer&gt;();
  
    private final List&lt;String&gt; options;
  
    /**
     * Construct a new {@link SelectionCell} with the specified options.
     *
     * @param options the options in the cell
     */
    public DynamicSelectionCell(List&lt;String&gt; options) {
      super("change");
      if (template == null) {
        template = GWT.create(Template.class);
      }
      this.options = new ArrayList&lt;String&gt;(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&lt;String&gt; 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 &amp;&amp; viewData.equals(value)) {
        clearViewData(key);
        viewData = null;
      }
  
      int selectedIndex = getSelectedIndex(viewData == null ? value : viewData);
      sb.appendHtmlConstant("&lt;select tabindex=\"-1\"&gt;");
      int index = 0;
      for (String option : options) {
        if (index++ == selectedIndex) {
          sb.append(template.selected(option));
        } else {
          sb.append(template.deselected(option));
        }
      }
      sb.appendHtmlConstant("&lt;/select&gt;");
    }
  
    private int getSelectedIndex(String value) {
      Integer index = indexForOption.get(value);
      if (index == null) {
        return -1;
      }
      return index.intValue();
    }
  }
  </code></pre>