How to load data BEFORE showing view/presenter?

[Matt H]

Hi.

If you poke around some of Google's GWT apps, you'll find that when
you click on anything which requires more data to be loaded, that a
'loading' sign is displayed at the top of the screen, and while
loading, it stays on the current view, and then when the data for the
next view has been downloaded, the loading sign is removed and the new
view is shown.

How can I implement this behavior?

[Matt H]

Anyone? Surely it's simple enough to do?

[ep]

depends on the MVP framework you use - gwtp for instance, already
supports it, if GWT MVP does not, then you can subclass presenter,
call it "IndicatingPresenter" and add one more lifecycle state,
because the presenter will be lazy loaded and shows a loading
indicator until its data is not available... when ready re-render the
view with data loaded.

[Matthew Hill]

Sorry, I should've mentioned that I'm using GWT 2.1 Activities + Places.

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[metalhammer29a]

I do not know the answer to this.
and would like to find out as I am in the similar situation.

However I have come across this class:
com.google.gwt.requestfactory.shared.RequestEvent

http://google-web-toolkit.googlecode.com/svn/javadoc/2.1/com/google/gwt/requestfactory/shared/RequestEvent.html

http://code.google.com/p/google-web-toolkit/source/browse/trunk/user/src/com/google/gwt/requestfactory/shared/RequestEvent.java?r=9033

and from Expenses app generated by Roo,
I can see it is used like below:

RequestEvent.register(eventBus, new RequestEvent.Handler() {
// Only show loading status if a request isn't serviced in
250ms.
private static final int LOADING_TIMEOUT = 250;

public void onRequestEvent(RequestEvent requestEvent) {
if (requestEvent.getState() == RequestEvent.State.SENT)
{
shell.getMole().showDelayed(LOADING_TIMEOUT);
} else {
shell.getMole().hide();
}
}
});

in UiBinder:
<g:NotificationMole animationDuration='0' message='loading...'
ui:field='mole'></g:NotificationMole>

in UiBinder java class:
@UiField NotificationMole mole;

NoticiationMole:
http://google-web-toolkit.googlecode.com/svn/javadoc/2.1/com/google/gwt/user/client/ui/NotificationMole.html

these are the pieces I have found.
but haven't put them together myself.

[metalhammer29a]

sorry, I believe I misunderstood your question.

[Thomas Broyer]

The trick is that the AcceptsOneWidget that you use for your
ActivityManager has to handle a 'null' value as *not* clearing the
display (in other words, give an AcceptsOneWidget of your own, do not
use a SimplePanel).
ActivityManager calls setWidget(null) when it stops the current
activity, and the next activity will then call setWidget with its view
when it's ready. If, when called with null, you don't do anything, the
previous activity will still be shown. And in your activities then
only call setWidget once you received the data.

The "loading" text is another story, and depends how you retrieve your
data; but metalhammer29a rightfully pointed to the NotificationMole
for the "display" part.

[Matthew Hill]

Thank you Thomas, that sounds very promising. I'll try that out.