/*
* 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.place.shared;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.shared.EventBus;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.Window.ClosingEvent;
import com.google.gwt.user.client.Window.ClosingHandler;
import java.util.logging.Logger;
/**
* In charge of the user's location in the app.
*/
public class PlaceController {
/**
* Default implementation of {@link Delegate}, based on {@link Window}.
*/
public static class DefaultDelegate implements Delegate {
public HandlerRegistration addWindowClosingHandler(ClosingHandler handler) {
return Window.addWindowClosingHandler(handler);
}
public boolean confirm(String message) {
return Window.confirm(message);
}
}
/**
* Optional delegate in charge of Window-related events. Provides nice
* isolation for unit testing, and allows customization of confirmation
* handling.
*/
public interface Delegate {
/**
* Adds a {@link ClosingHandler} to the Delegate.
*
* @param handler a {@link ClosingHandler} instance
* @return a {@link HandlerRegistration} instance
*/
HandlerRegistration addWindowClosingHandler(ClosingHandler handler);
/**
* Called to confirm a window closing event.
*
* @param message a warning message
* @return true to allow the window closing
*/
boolean confirm(String message);
}
private static final Logger log = Logger.getLogger(PlaceController.class.getName());
private final EventBus eventBus;
private final Delegate delegate;
private Place where = Place.NOWHERE;
/**
* Create a new PlaceController with a {@link DefaultDelegate}. The
* DefaultDelegate is created via a call to GWT.create(), so an alternative
* default implementation can be provided through <replace-with> rules
* in a {@code .gwt.xml} file.
*
* @param eventBus the {@link EventBus}
*/
public PlaceController(EventBus eventBus) {
this(eventBus, (Delegate) GWT.create(DefaultDelegate.class));
}
/**
* Create a new PlaceController.
*
* @param eventBus the {@link EventBus}
* @param delegate the {@link Delegate} in charge of Window-related events
*/
public PlaceController(EventBus eventBus, Delegate delegate) {
this.eventBus = eventBus;
this.delegate = delegate;
delegate.addWindowClosingHandler(new ClosingHandler() {
public void onWindowClosing(ClosingEvent event) {
String warning = maybeGoTo(Place.NOWHERE);
if (warning != null) {
event.setMessage(warning);
}
}
});
}
/**
* Returns the current place.
*
* @return a {@link Place} instance
*/
public Place getWhere() {
return where;
}
/**
* Request a change to a new place. It is not a given that we'll actually get
* there. First a {@link PlaceChangeRequestEvent} will be posted to the
* event bus. If any receivers post a warning message to that event, it will
* be presented to the user via {@link Delegate#confirm(String)} (which is
* typically a call to {@link Window#confirm(String)}). If she cancels, the
* current location will not change. Otherwise, the location changes and a
* {@link PlaceChangeEvent} is posted announcing the new place.
*
* @param newPlace a {@link Place} instance
*/
public void goTo(Place newPlace) {
log().fine("goTo: " + newPlace);
if (getWhere().equals(newPlace)) {
log().fine("Asked to return to the same place: " + newPlace);
return;
}
String warning = maybeGoTo(newPlace);
if (warning == null || delegate.confirm(warning)) {
where = newPlace;
eventBus.fireEvent(new PlaceChangeEvent(newPlace));
}
}
/**
* Visible for testing.
*/
Logger log() {
return log;
}
private String maybeGoTo(Place newPlace) {
PlaceChangeRequestEvent willChange = new PlaceChangeRequestEvent(
newPlace);
eventBus.fireEvent(willChange);
String warning = willChange.getWarning();
return warning;
}
}