According to this FAQ, when GWT bootstraps, onModuleLoad is supossed to run before HTML body's onload event. The process detailed within that FAQ works like this:
1. The HTML document is fetched and parsing begins.
...
9. externalScriptOne.js completes. The document is ready, so onModuleLoad() fires.
...
12. body.onload() fires, in this case showing an alert() box.
But in my tests, i have checked that it doesnt work this way. Or at least not in every browser (oddly, Google Chrome in particular doesn't stick to this kind of behaviour). For example, I have this little test involving onModuleLoad and body.onLoad:
public void onModuleLoad() {
runTestFunction();
}
private native void runTestFunction() /*-{
console.log("GWT's onModuleLoad");
$wnd.loaded=true;
}-*/;
And:
<body onload="console.log('body.onLoad');if(loaded!=null) console.log('loaded var is set');">
If i launch firefox, and run this example, the console will show this:
GWT's onModuleLoad
body.onLoad
loaded var is set
But in Chrome:
body.onLoad
Uncaught ReferenceError: loaded is not defined
GWT's onModuleLoad
In the latter, onModuleLoad runs the last, thus "loaded" var is not yet available and body.onLoad code cant use it.
And what Im trying to achieve? I want some handwritten Javascript that runs within body.onload to interact with my GWT code. In this example i use this dummy "loaded" var, but in the future it should be able to call GWT functions written in Java. The problem is that i need to make sure that onModuleLoad runs first so it can export the variables and methods for javascript to access them.
So, what am i missing? Is this behaviour as unreliable as it looks like, or am i doing something wrong?
PS: i have a plan B to achieve this which is proved to work, but first i want to make sure that it isnt possible to do it this way since this should be the preferred method.
First, the latest version of the doc is at http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideBootstrap
And it says (even the GWT 1.5 version you were looking at) that "onModuleLoad() can be called at any point after the outer document has been parsed", which includes before and after window.onload.
As the doc says, GWT loads your code in an iframe (used here as a sandbox), which is asynchronous; so your code loads when both the iframe and the "body" are loaded. Depending on the time needed to load the iframe, that can be before or after window.onload (in the example, they assume it loads right away, which could be the case when the *.cache.* file is effectively in the browser's cache).
But the rule of thumb is that GWT tries hard (at least the built-in linkers) to make things start asynchronously so that it doesn't break loading of other external resources (stylesheets and images, for instance). That implies that it cannot be guaranteed to run before the window.onload (they could have guaranteed to run after window.onload, but why wait?)
Related
l split my GWT code in different different modules like
PrintPermit.gwt.xml
EmployeeResponse.gwt.xml
Rejected.gwt.xml
and every module has its own entry point class
in my HTML host page I am calling script like
ae.init.EmployeeResponse.nocache.js
I have a menu like
Print Application
Reject Application
New application
whenever user will click on new application default new application will open
as I declare EmployeeResponse.nocache.js statically in my HTML host page.
now I want to call other modules on click button print and reject button
how can i call nocache js for print and reject modules. is there any way to dynamic call.
please help me guys.
Here's how I've done it in the past:
First of all, in the module you want to export, you need to make sure that the code you're going to export doesn't end up obfuscated. This can be accomplished with the liberal use of #JsType; this is the new way of exporting JS, available in GWT 2.8 (as opposed to JSNI).
Your module's entry point onModuleLoad can be empty; it doesn't need to do anything.
Include your JS in the HTML you want to use (maybe the same page as your "main" module)
Check JSInterop documentation (perhaps the one available here) on how you can use native JS in your GWT app (because now, your GWT module became native JS). Import the classes via JSInterop from your library, and use them.
Please be aware of the async nature of the GWT JS loading; your library will be loading in an async manner, just like any JS application (and therefore, it won't be available immediately when your page loads). To overcome this, I've placed a call to a native JS function in my library's onModuleLoad function (i.e. to make sure you notify any potential listeners that the code has loaded; because when onModuleLoad runs, the code surely loaded).
There is a example of an InterAppEventBus:
https://github.com/sambathl/interapp-eventbus
which shows the communication between two GWT applications.
I have adopted it and replaced JSNI with Elemental2 and WebStorage:
https://github.com/FrankHossfeld/InterAppEventBus
Hope that helps.
You can achieve this through separate Html file for each module.
So first of all create separate html for each application e.g. PrintPermit.html and specify corresponding nocache.js in each html.
then on your buttons in menu, add click handlers and in each on click load a corresponding html through Window.open()
e.g. for PrintPermit,
printPermitButton.addClickHandler(new ClickHandler{
#Override
public void onClick(ClickEvent arg0) {
String s = GWT.getHostPageBaseURL() + "PrintPermit.html";
Window.open(s, "PrintPermit", "");
}
});
Please note the window.open will open in new tab in browser, you can also use gwt iframe to open html in same browser page.
Each module will have corresponding nocache.js and will be loaded through html using Window.open()
GWT auto generate the JavaScript code.
I could not understand the generated code event mechanism.
for instance, which function run when I click on a button?
I would love to see the javascript that GWT generates for button with explanations
For event handling, GWT attaches a EventListener (generally, your widget) as an expando property (called __listener) of the elements. The events are then all handled by a single dispatch method that looks at the __listener expando of the event's target and dispatches the event to it. Of course, the dispatch method does a bit more (event previewing, entry/finally scheduled commands, etc.)
This dance is (or at least was) required to avoid memory leaks in browsers (mainly IE). You can find more details in the GWT wiki: https://code.google.com/p/google-web-toolkit/wiki/DomEventsAndMemoryLeaks
When you develop in GWT, you don't care about JavaScript.
You should look at the Java code, and search for a function that handles the click event for your button.
When you compile the code Compiler will generate the autoamted Javascript functions ...And that too in compressed (thats depends on your compile type).
It is very hard to find the corresponding function and widget id because those are generated by compiler ..So its better to debug your gwt code is hosted mode ..
Even you want to read the generated code while compiling give the compilation type to
DETAILED, which improves on PRETTY with even more detail (such as very verbose variable names)
Still more details available here .
You should use GWT Compiler options STYLE whenever you need to understand the GWT's output js. GWT by default compresses and obfuscates the javascript output as it uses OBF as default value for STYLE.
To prevent compression and obfuscation you can use PRETTY or DETAILED as the parameter to STYLE argument.
NOTE: You should always use OBF mode for production as it ensures smallest bandwidth usage along with obfuscation.
Reference - https://developers.google.com/web-toolkit/doc/latest/DevGuideCompilingAndDebugging#DevGuideCompilerOptions
In GWT web/production mode, Java code is complied into Javascript code that is rendered in the browser.
Also,I have always thought that in GWT development mode, GWT developer plugin compiles my Java code into JavaScript to render it in the browser. But after reading on some site, I came to know that there's no compiling of code to JavaScript to view it in the browser in development mode.
So, I wonder: What are all these widgets I see in the browser during this mode if they aren't JavaScript code?. I don't understand it.
Please help understanding this.
The crux of the Dev Mode is that your code runs in Java. This is a prerequisite if you can use a standard Java debugger. You'll find a high-level overview in the GWT documentation.
The magic happens with JSNI methods and overlay types: when a class is loaded, all its JSNI methods are extracted and their JS body is sent to the browser, ready to be executed (as JavaScript then), and the class is rewritten on the fly to reimplement the JSNI method to make a call to the browser (via the Dev Plugin you installed there and is triggered by ?gwt.codesvr= in the URL) to execute the corresponding JS function. This is the reason why Java objects are seen as opaque handles in JSNI methods; they're assigned a numeric ID to pair the Java object with a dummy JS object on the server-side. A similar though more complex rewriting is done for overlay types, and the same ID mapping is used when JS objects are passed to Java code (as overlay types).
BTW, Super Dev Mode compiles to JavaScript (almost) on the fly.
Im new about this technology, but I would like to know if is possible to create new object (html elements, such div/span/and so on...) dinamically on server and send it to the client, or if i can just load the ones made on client-side when i develop it in the application.
I don't ask how to do it (i think its a delicate argument), but if I can, and (if yes) where i can get some stuff/example/tutorial to do this.
Example
What i usually do :
...
public void onSuccess(Boolean result) {
if(result) {
myFunction();
}
}
...
myFunction() {
InlineLabel label=new InlineLabel();
this.add(label)
}
What im looking for :
...
public void onSuccess(InlineLabel result) {
this.add(result)
}
So, i don't need to load in advance the Object, but load them only if i click on some button (or if i perform an action). This will save a lot of code (that is inutil, if i don't do any action) loaded (as JavaScript) on the client.
As usual, thanks for your time!
GWT does not support the pattern you showed, but you can achieve a similar effect with "code splitting": read http://code.google.com/webtoolkit/doc/latest/DevGuideCodeSplitting.html
With code splitting, the client only downloads the script it needs right away (configured by the developer). If, for example, the user navigates to a more complex area of the UI that requires more widgets, additional code will be downloaded.
I'm not entirely sure I understand your question, but please feel free to amend your question or post a comment if I've missed the mark.
The host page
A GWT app is loaded in the following (simplified) process:
A host page (HTML) is loaded
A bootstrapping script is loaded
A compiled app script is loaded
The host page can contain any HTML you want. The only requirement is that you include a <script> element that loads the GWT bootstrapping script.
As a result, you can have the server return a page that contains any server-generated markup you like.
Server-rendered HTML at runtime
Once your app is running, you can send off asynchronous requests in your code to retrieve arbitrary data from the server. One option is to retrieve server-generated HTML and insert it into your application.
For this option, you'll want to instantiate an HTML widget, then use its setHTML method to insert the server-generated markup into the widget.
Client-generated
As an alternative, you can retrieve structured data from the server via GWT RPC. Objects created on a Java-based server are serialised by GWT on the server and deserialised on the client back into regular objects. You can then pull data out of these objects using accessor methods (getName, getId, etc.). At this point, you have several options:
Generate some HTML using StringBuilder and the like, then use setHTML on an HTML widget.
Generate DOM elements with the DOM class
Set the data into widgets and add them to panels or the root panel.
I've encountered what seems like a chicken & egg problem, and have what I think is a logical solution. However, it occurred to me that others must have encountered something similar, so I figured I'd float it out there for the masses.
The situation is that I want to use dojo's addOnLoad function to queue up a number of callbacks which should be executed after the DOM has completed rendering on the client side. So what I'm doing is as follows:
<html>
<head>
<script type="text/javascript" src="dojo.xd.js"></script>
...
</head>
<body>
...
<script type="text/javascript">
dojo.addOnLoad( ... );
dojo.addOnLoad( ... );
...
</script>
</body>
</html>
Now, the issue is that I seem to be calling dojo.addOnLoad before the entire Dojo library has been downloaded the browser. This makes sense in a way, because the inline SCRIPT contents should be executed before the entire DOM is loaded (and the normal body onload callback is triggered).
My question is this - is my approach sound, or would it make more sense to register a normal/standard body onload JavaScript callback to call a function, which does the same work that each of the dojo.addOnLoads is doing in the SCRIPT block. Of course, this begs the question, why would you ever then use dojo.addOnLoad if you're not guaranteed that the Dojo library will be loaded prior to using the library?
Hopefully this situation makes sense to someone other than me. Seems like someone else may have encountered this situation.
Thoughts?
Best Regards,
Adam Rice
You're doing it correctly. External Javascript files are loaded and executed synchronously in order, so by the time it reaches your dojo.addOnLoad( ... ); Dojo has loaded. Use dojo.addOnLoad instead of window.onload for two reasons:
it fires earlier, because it utilizes DOMContentLoaded
it handles asynchronous loading of dojo.require by postponing the execution until all required scripts have been read
Explained in DojoCampus as (dojo.addOnLoad):
dojo.addOnLoad is a fundamental aspect
of using Dojo. Passing addOnLoad a
function will register the function to
run when the Dom is ready. This
differs slightly from document.ready
and body.onload in that addOnLoad
waits until all dojo.require() (and
their recursive dependencies) have
loaded before firing.
This might have nothing to do with your problem, but ive just had a case where I had the same symptoms. For me everything worked fine for Firefox, Chrome etc, but not IE8.
I was getting what looked like dojo not being loaded, an error in IE8 saying that dojo was undefined (but not all the time) and i could strip everything down to just style sheets and importing dojo and still get the error.
I was running a local google app engine development server. This looks to be based on pythons SimpleHTTPServer which in turn uses SocketServer.BaseServer. This has BaseServer.request_queue_size which defaults to 5 - i couldn't find anything in app engine which overrode this value so i guess the development google app engine server has an upper limit of 5 connections.
Using regedit and going to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
“MaxConnectionsPerServer”=dword:00000010
“MaxConnectionsPer1_0Server”=dword:0000010
This shows that IE was going to try and open up to 10 simultaneous connections. I edited these two keys and made them 2 and restarted the computer, the problem went away.