com.google.gwt.place.shared.PlaceController.java Source code

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Here is the source code for com.google.gwt.place.shared.PlaceController.java

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/*
 * 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.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 com.google.web.bindery.event.shared.EventBus;

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;

    /**
     * Legacy method tied to the old location for {@link EventBus}.
     * 
     * @deprecated use {@link #PlaceController(EventBus)}
     */
    @Deprecated
    public PlaceController(com.google.gwt.event.shared.EventBus eventBus) {
        this((EventBus) eventBus);
    }

    /**
     * Legacy method tied to the old location for {@link EventBus}.
     * 
     * @deprecated use {@link #PlaceController(EventBus, Delegate)}
     */
    @Deprecated
    public PlaceController(com.google.gwt.event.shared.EventBus eventBus, Delegate delegate) {
        this((EventBus) eventBus, delegate);
    }

    /**
     * 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;
    }
}