/*
* 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.activity.shared;
import com.google.gwt.event.shared.ResettableEventBus;
import com.google.gwt.event.shared.UmbrellaException;
import com.google.gwt.place.shared.PlaceChangeEvent;
import com.google.gwt.place.shared.PlaceChangeRequestEvent;
import com.google.gwt.user.client.ui.AcceptsOneWidget;
import com.google.gwt.user.client.ui.IsWidget;
import com.google.web.bindery.event.shared.EventBus;
import com.google.web.bindery.event.shared.HandlerRegistration;
import java.util.LinkedHashSet;
import java.util.Set;
/**
* Manages {@link Activity} objects that should be kicked off in response to
* {@link PlaceChangeEvent} events. Each activity can start itself
* asynchronously, and provides a widget to be shown when it's ready to run.
*/
public class ActivityManager implements PlaceChangeEvent.Handler, PlaceChangeRequestEvent.Handler {
/**
* Wraps our real display to prevent an Activity from taking it over if it is
* not the currentActivity.
*/
private class ProtectedDisplay implements AcceptsOneWidget {
private final Activity activity;
ProtectedDisplay(Activity activity) {
this.activity = activity;
}
public void setWidget(IsWidget view) {
if (this.activity == ActivityManager.this.currentActivity) {
startingNext = false;
showWidget(view);
}
}
}
private static final Activity NULL_ACTIVITY = new AbstractActivity() {
public void start(AcceptsOneWidget panel, com.google.gwt.event.shared.EventBus eventBus) {
}
};
private final ActivityMapper mapper;
private final EventBus eventBus;
/*
* Note that we use the legacy class from com.google.gwt.event.shared, because
* we can't change the Activity interface.
*/
private final ResettableEventBus stopperedEventBus;
private Activity currentActivity = NULL_ACTIVITY;
private AcceptsOneWidget display;
private boolean startingNext = false;
private HandlerRegistration handlerRegistration;
/**
* Create an ActivityManager. Next call {@link #setDisplay}.
*
* @param mapper finds the {@link Activity} for a given
* {@link com.google.gwt.place.shared.Place}
* @param eventBus source of {@link PlaceChangeEvent} and
* {@link PlaceChangeRequestEvent} events.
*/
public ActivityManager(ActivityMapper mapper, EventBus eventBus) {
this.mapper = mapper;
this.eventBus = eventBus;
this.stopperedEventBus = new ResettableEventBus(eventBus);
}
/**
* Returns an event bus which is in use by the currently running activity.
* <p>
* Any handlers attached to the returned event bus will be de-registered when
* the current activity is stopped.
*
* @return the event bus used by the current activity
*/
public EventBus getActiveEventBus() {
return stopperedEventBus;
}
/**
* Deactivate the current activity, find the next one from our ActivityMapper,
* and start it.
* <p>
* The current activity's widget will be hidden immediately, which can cause
* flicker if the next activity provides its widget asynchronously. That can
* be minimized by decent caching. Perenially slow activities might mitigate
* this by providing a widget immediately, with some kind of "loading"
* treatment.
*/
public void onPlaceChange(PlaceChangeEvent event) {
Activity nextActivity = getNextActivity(event);
Throwable caughtOnStop = null;
Throwable caughtOnCancel = null;
Throwable caughtOnStart = null;
if (nextActivity == null) {
nextActivity = NULL_ACTIVITY;
}
if (currentActivity.equals(nextActivity)) {
return;
}
if (startingNext) {
// The place changed again before the new current activity showed its
// widget
caughtOnCancel = tryStopOrCancel(false);
currentActivity = NULL_ACTIVITY;
startingNext = false;
} else if (!currentActivity.equals(NULL_ACTIVITY)) {
showWidget(null);
/*
* Kill off the activity's handlers, so it doesn't have to worry about
* them accidentally firing as a side effect of its tear down
*/
stopperedEventBus.removeHandlers();
caughtOnStop = tryStopOrCancel(true);
}
currentActivity = nextActivity;
if (currentActivity.equals(NULL_ACTIVITY)) {
showWidget(null);
} else {
startingNext = true;
caughtOnStart = tryStart();
}
if (caughtOnStart != null || caughtOnCancel != null || caughtOnStop != null) {
Set<Throwable> causes = new LinkedHashSet<Throwable>();
if (caughtOnStop != null) {
causes.add(caughtOnStop);
}
if (caughtOnCancel != null) {
causes.add(caughtOnCancel);
}
if (caughtOnStart != null) {
causes.add(caughtOnStart);
}
throw new UmbrellaException(causes);
}
}
/**
* Reject the place change if the current activity is not willing to stop.
*
* @see com.google.gwt.place.shared.PlaceChangeRequestEvent.Handler#onPlaceChangeRequest(PlaceChangeRequestEvent)
*/
public void onPlaceChangeRequest(PlaceChangeRequestEvent event) {
event.setWarning(currentActivity.mayStop());
}
/**
* Sets the display for the receiver, and has the side effect of starting or
* stopping its monitoring the event bus for place change events.
* <p>
* If you are disposing of an ActivityManager, it is important to call
* setDisplay(null) to get it to deregister from the event bus, so that it can
* be garbage collected.
*
* @param display an instance of AcceptsOneWidget
*/
public void setDisplay(AcceptsOneWidget display) {
boolean wasActive = (null != this.display);
boolean willBeActive = (null != display);
this.display = display;
if (wasActive != willBeActive) {
updateHandlers(willBeActive);
}
}
private Activity getNextActivity(PlaceChangeEvent event) {
if (display == null) {
/*
* Display may have been nulled during PlaceChangeEvent dispatch. Don't
* bother the mapper, just return a null to ensure we shut down the
* current activity
*/
return null;
}
return mapper.getActivity(event.getNewPlace());
}
private void showWidget(IsWidget view) {
if (display != null) {
display.setWidget(view);
}
}
private Throwable tryStart() {
Throwable caughtOnStart = null;
try {
/*
* Wrap the actual display with a per-call instance that protects the
* display from canceled or stopped activities, and which maintains our
* startingNext state.
*/
currentActivity.start(new ProtectedDisplay(currentActivity), stopperedEventBus);
} catch (Throwable t) {
caughtOnStart = t;
}
return caughtOnStart;
}
private Throwable tryStopOrCancel(boolean stop) {
Throwable caughtOnStop = null;
try {
if (stop) {
currentActivity.onStop();
} else {
currentActivity.onCancel();
}
} catch (Throwable t) {
caughtOnStop = t;
} finally {
/*
* Kill off the handlers again in case it was naughty and added new ones
* during onstop or oncancel
*/
stopperedEventBus.removeHandlers();
}
return caughtOnStop;
}
private void updateHandlers(boolean activate) {
if (activate) {
final HandlerRegistration placeReg = eventBus.addHandler(PlaceChangeEvent.TYPE, this);
final HandlerRegistration placeRequestReg =
eventBus.addHandler(PlaceChangeRequestEvent.TYPE, this);
this.handlerRegistration = new HandlerRegistration() {
public void removeHandler() {
placeReg.removeHandler();
placeRequestReg.removeHandler();
}
};
} else {
if (handlerRegistration != null) {
handlerRegistration.removeHandler();
handlerRegistration = null;
}
}
}
}