user/src/com/google/gwt/cell/client/AbstractCell.java

/*
 * 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.dom.client.BrowserEvents;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.event.dom.client.KeyCodes;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

/**
 * A default implementation of the {@link Cell} interface.
 * 
 * <p>
 * <h3>Examples</h3>
 * <dl>
 * <dt>Read only cell</dt>
 * <dd>{@example com.google.gwt.examples.cell.CellExample}</dd>
 * <dt>Cell with events</dt>
 * <dd>{@example com.google.gwt.examples.cell.CellWithEventsExample}</dd>
 * <dt>Interactive cell</dt>
 * <dd>{@example com.google.gwt.examples.cell.InteractionCellExample}</dd>
 * <dt>Editable cell</dt>
 * <dd>{@example com.google.gwt.examples.cell.EditableCellExample}</dd>
 * </dl>
 * </p>
 * 
 * @param <C> the type that this Cell represents
 */
public abstract class AbstractCell<C> implements Cell<C> {

  /**
   * The unmodifiable set of events consumed by this cell.
   */
  private Set<String> consumedEvents;

  /**
   * Construct a new {@link AbstractCell} with the specified consumed events.
   * The input arguments are passed by copy.
   * 
   * @param consumedEvents the {@link com.google.gwt.dom.client.BrowserEvents
   *          events} that this cell consumes
   * 
   * @see com.google.gwt.dom.client.BrowserEvents
   */
  public AbstractCell(String... consumedEvents) {
    Set<String> events = null;
    if (consumedEvents != null && consumedEvents.length > 0) {
      events = new HashSet<String>();
      for (String event : consumedEvents) {
        events.add(event);
      }
    }
    init(events);
  }

  /**
   * Construct a new {@link AbstractCell} with the specified consumed events.
   * 
   * @param consumedEvents the events that this cell consumes
   */
  public AbstractCell(Set<String> consumedEvents) {
    init(consumedEvents);
  }

  public boolean dependsOnSelection() {
    return false;
  }

  public Set<String> getConsumedEvents() {
    return consumedEvents;
  }

  public boolean handlesSelection() {
    return false;
  }

  /**
   * Returns false. Subclasses that support editing should override this method
   * to return the current editing status.
   */
  public boolean isEditing(Context context, Element parent, C value) {
    return false;
  }

  /**
   * {@inheritDoc}
   * 
   * <p>
   * If you override this method to add support for events, remember to pass the
   * event types that the cell expects into the constructor.
   * </p>
   */
  public void onBrowserEvent(Context context, Element parent, C value,
      NativeEvent event, ValueUpdater<C> valueUpdater) {
    String eventType = event.getType();
    // Special case the ENTER key for a unified user experience.
    if (BrowserEvents.KEYDOWN.equals(eventType) && event.getKeyCode() == KeyCodes.KEY_ENTER) {
      onEnterKeyDown(context, parent, value, event, valueUpdater);
    }
  }

  public abstract void render(Context context, C value, SafeHtmlBuilder sb);

  /**
   * {@inheritDoc}
   * 
   * <p>
   * This method is a no-op and returns false. If your cell is editable or can
   * be focused by the user, override this method to reset focus when the
   * containing widget is refreshed.
   * </p>
   */
  public boolean resetFocus(Context context, Element parent, C value) {
    return false;
  }

  public void setValue(Context context, Element parent, C value) {
    SafeHtmlBuilder sb = new SafeHtmlBuilder();
    render(context, value, sb);
    parent.setInnerHTML(sb.toSafeHtml().asString());
  }

  /**
   * Called when the user triggers a <code>keydown</code> event with the ENTER
   * key while focused on the cell. If your cell interacts with the user, you
   * should override this method to provide a consistent user experience. Your
   * widget must consume <code>keydown</code> events for this method to be
   * called.
   * 
   * @param context the {@link Context} of the cell
   * @param parent the parent Element
   * @param value the value associated with the cell
   * @param event the native browser event
   * @param valueUpdater a {@link ValueUpdater}, or null if not specified
   */
  protected void onEnterKeyDown(Context context, Element parent, C value,
      NativeEvent event, ValueUpdater<C> valueUpdater) {
  }

  /**
   * Initialize the cell.
   * 
   * @param consumedEvents the events that the cell consumes
   */
  private void init(Set<String> consumedEvents) {
    if (consumedEvents != null) {
      this.consumedEvents = Collections.unmodifiableSet(consumedEvents);
    }
  }
}