Question

I m new to GWT, and I m sure this is answered in SO somewhere but I ve yet to find

I downloaded the GWT 2.0 eclipse plugin, and was pleased to see it comes with a starter project.

However, I was surprised that when running it, there is an unpleasent flickering...

The text loads without the CSS first
It takes a while untill the select box apears

(If you don t see the flicker, try and press F5 to refresh)

All mature GWT apps seem to have a loader before that but I didn t find an easy, standard way to add it.

It seems this app loads in this order: (correct me please if I mixed it up, its only my guess)

Basic layout HTML,
All JavaScript, and CSS
Runs the logic on the "onload" event (soonest time your compiled javaScript can start - ?)

So I can t programmatically add a loading spinner before GWT was loaded, a bit of a catch 22 for me

Am I missing something basic? is there a best practice way to add that initial spinner?

I was thinking simply adding a div with an animated gif, and in the onload event - hide it.

But I m sure there is something better.

Let me know if this is a duplicate question

Update: found this related question, not answering mine though...

Answer 1

I ve handled this problem before by not using the GWT module to load CSS, but loading it directly in the tag itself. If you do this, the browser will always load the CSS first, even before the GWT JS is loaded.

This means you ll lose a bit of flexibility and speed, but its the only workaround I ve used so far.

EDIT: Extra info cause I want the bounty :D

If you do not remove the <inherits name= com.google.gwt.user.theme.standard.Standard /> from your module.gwt.xml file, then the GWT standard theme is loaded in the JS file that GWT creates. This JS file loads after the HTML page renders, and injects the CSS after load. Hence the flicker.

To avoid the flicker, you can comment out that line and insert your own stylesheet into the <head> of your HTML file. This ensures your CSS loads before the HTML renders, avoiding any flicker. If you really want the GWT theme, you get it out of the source code.

To use a spinner with GWT is quite easy. One simple way would be to keep it in a div with an id in the HTML file itself. Then, in the onModuleLoad(), simply hide that div by calling RootPanel.get("spinner").setVisible(false);

That should show the spinner till GWT loads itself.

Answer 2

Here s what we do to implement a spinner.

You put something like the following HTML just below the script line that loads your application (ie. the one with nocache.js). e.g.:

    <div id="loading">
        <div id="loading-msg">
            <img src="icons/loading-page.gif" lt="loading">
            <span>Loading the application, please wait...</span>
        </div>    
    </div>

Then in your application EntryPoint you reach into the page using the DOM and remove that div. e.g.

final RootPanel loading = RootPanel.get("loading");
if (loading != null) {
    DOM.removeChild(RootPanel.getBodyElement(),
                    loading.getElement());
}

Answer 3

Ehrann: I m afraid the practice mentioned in the above answers is the only way for now. GWT doesn t provide similar features to show/hide a "loading" frame "on the fly". I guess one of the reason is that this requirement is not so "common" for all GWT users, one person might want a very different style of the "loading" than others. So you have to do that by yourself.

You can have a look at the GXT showcase page (based on GWT too): http://www.extjs.com/explorer/ for how they do that. For the source of it, download Ext GWT 2.1.0 SDK here: http://www.extjs.com/products/gxt/download.php and check the samples/explorer folder after extracting it. For details see the edit below:

EDIT

Check the source code for http://www.extjs.com/examples/explorer.html and you can see a div with id "loading". For each samples (extending Viewport), GXT.hideLoadingPanel(loadingPanelId) is called in onAttach() (the initialization), which hides the loading frame.

Check source code of Viewport here

Check source code of GXT.hideLoadingPanel here

You can do it in a similar way.

Answer 4

You could put an HTML loading message in the host page (use style attributes or embed the style tag in the header to make sure that it s styled), and remove the message once your modules has loaded, e. g. Document.get().getBody() with .setInnerHTML("") or .removeChild(), and then present your application programmatically however you want.

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