Masterpiece!
On Aug 22, 7:03 pm, Jason Essington <[EMAIL PROTECTED]> wrote:
> I hear this often enough that I thought I'd offer up a little story
> that'll maybe help some new comers to GWT from falling into this
> fairly common problem.
>
> At issue is that the demos that come with GWT tend to lean heavily on
> anonymous inner classes, which sometimes lead to misunderstandings
> about what is really going on in the code. So without further ado, the
> pitfall:
>
> protected String someString;
>
> public void callService(){
> SomeServiceAsync service = (SomeServiceAsync)
> GWT.create(SomeService.class);
> ((ServiceDefTarget)
> service).setServiceEntryPoint(GWT.getModuleBaseURL()+"SomeService";
>
> service.doSomething( new AsyncCallback<String>(){
> public void onFailure(Throwable caught) {
> Window.alert("DOH!");
> }
> public void onSuccess(String result) {
> someString = result;
> }
> });
>
> Window.alert(someString);
>
> }
>
> And inevitably we'll hear "My RPC doesn't work" or "It doesn't work
> the first time, but after that it is fine"
>
> The problem here is that the unwitting user, new to Asynchronous
> programming has tried to make the asynchronous request synchronous.
>
> How's that? Well let me translate that little bit of java code into a
> plain english situation that you could encounter any old day.
>
> Imagine if you will ...
>
> You are sitting on the couch watching TV, and knowing that you are out
> of beer, you ask your spouse to please run down to the liquor store
> and fetch you some. As soon as you see your spouse walk out the front
> door, you get up off the couch and trundle into the kitchen and open
> the fridge. To your surprise, there is no beer!
>
> Well of course there is no beer, your spouse is still on the trip to
> the liquor store. You've gotta wait until [s]he returns before you can
> expect to have a beer.
>
> So, lets rewrite our little RPC with that little tidbit in mind.
>
> protected Fridge kitchenFridge;
>
> public void getMeSomeBeer(){
> SpouseServiceAsync spouse = (SpouseServiceAsync)
> GWT.create(SpouseService.class);
> ((ServiceDefTarget)
> service).setServiceEntryPoint(GWT.getModuleBaseURL()+"SpouseService";
>
> spouse.goToLiquorStorePlease(Beer.SIX_PACK, new
> AsyncCallback<Beer>(){
> public void onFailure(Throwable caught) {
> Window.alert("DOH!");
> }
> public void onSuccess(Beer your6pack) {
> kitchenFridge.put(your6pack);
> goDrinkYourBeer();
> }
> });
>
> }
>
> public Burp goDrinkYourBeer(){
> Beer beer = kitchenFridge.get(Beer.BOTTLE);
> beer.open();
> /* its your beer, you figure it out */
> return new Burp(Burp.LOUD);
>
> }
>
> So there you have it, A subtle but very important difference.
>
> Now, once that little revelation hits home, the very next thing that
> folks new to GWT ask is, "But I really need it to be Synchronous"
>
> No, you don't!, and in fact you really don't want it to be ...
>
> Same scenario, only synchronous
> ... spouse walks out the door ...
> now, the entire world around you stops, you don't get to breath,
> answer the door, or finish watching your show while [s]he runs across
> town to fetch your beer. You just get to sit there not moving a
> muscle, and turning blue until you lose consciousness ... waking up
> some indefinite time later surrounded by EMTs and a spouse saying oh,
> hey, I got your beer.
>
> Synchronous requests in the web browser lock up the entire browser,
> you can't switch tabs, can't browse other pages, and in some cases
> can't even close the browser until that request returns. That is the
> definition of naughty behavior on the part of the programmer. That is
> the reason that GWT doesn't provide a way to perform synchronous
> requests.
>
> Hopefully this little plain english scenario will help some
> programmers new to GWT navigate the sometimes confusing concept that
> is the Asynchronous request.
>
> -jason
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Google Web Toolkit" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/Google-Web-Toolkit?hl=en
-~----------~----~----~----~------~----~------~--~---
