/**
* 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);
}
}
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;
}