GWT: How do I get a reference to a button from the RootPanel?

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I'm using GWT 2.4. In my onModuleLoad method, given a string id, how do I get a reference to an existing button on the page from the RootPanel object? I'm trying this

public void onModuleLoad() {
    final Button submitButton = (Button) RootPanel.get("submit");

but getting the compile error, "Cannot cast from RootPanel to Button".


I thought using an iterator would heal the pain, but no dice. Here is the default HTML loaded (notice the button with id="submit") ...


    <form name="f">

        File name: <input type="text" size="25" id="filename" name="filename"

            value="" /> <input type="button" id="submit" name="submit"

            value="Submit" /> <input type="hidden" name="curId" id="curId"

            value="" />



<div id="content"></div>

but this code in onModuleLoad causes a NullPointerException (because the submitButton id can't be found) ...

public void onModuleLoad() {

    final Button submitButton = (Button) getWidgetById("submit");

private Widget getWidgetById(final String id) {
    Widget eltToFind = null;
    final Iterator<Widget> iter = RootPanel.get().iterator();
    while (iter.hasNext()) {
        final Widget widget =;
        final Element elt = widget.getElement();
        if (elt.getId() != null && elt.getId().equals(id)) {
            eltToFind = widget;
        } // if
    } // while
    return eltToFind;

Thanks, - Dave

You can get your input element using Document.get().getElementById("submit").<InputElement>cast(), but you won't be able to get a Button widget out of it.

If you change your code to read <button type="button" id="submit" name="submit" value="Submit"> instead of <input> (the type=button part is technically not needed, but some browsers will treat it like a type=submit if you don't), then you can use Button.wrap():

Button button = Button.wrap(Document.get().getElementById("submit"));

Panels Widgets, Lightweight Metrics Linkers Reference Command Line Tools GWT Class API Jre Panels in GWT are much like their layout counterparts in other user interface libraries. RootPanel.get() gets a singleton panel that wraps the HTML document's as form elements, buttons, tables, and text should still be laid out naturally. Failing to do this may cause these widgets to leak memory. This method is called automatically by widgets' wrap methods (e.g. Button.wrap( This method may not be called on any widget whose element is contained in another widget. This is to ensure that the DOM and Widget hierarchies cannot get into an

Some of GWT widgets have static method wrap() which allows to convert DOM elements to widget instances.

Button submit = Button.wrap(DOM.getElementById("submit"));

FAQ - UI, As an example, suppose you were trying to create a layout with two buttons, one on EAST); vertPanel.add(dockPanel); RootPanel.get().add(vertPanel); if you remove a button from the app, make sure you also remove * its reference from� A standard push-button widget. CSS Style Rules.gwt-Button the outer element. Example public class ButtonExample implements EntryPoint { public void onModuleLoad() { // Make a new button that does something when you click it.

The get() method returns the RootPanel associated with the browser element, not the widget with that name. A RootPanel is a subclass of ComplexPanel, so I think your best bet is to use the methods from ComplexPanel to iterate through the widgets and so find the one that you want that way.

[GWT] Tutorials Overview Build a GWT App. Introduction Create , For instance, a Button widget becomes a true HTML <button> rather than a If you're interested in taking a peek at the API reference for the GWT widgets There are two ways you can use a Root panel, either to generate the� I am new to Java and GWT. From what I understand, the concept of GWT is not to navigate between pages but rather use the same RootPanel and change the content inside. My question is how to do so if I

Wrap creates a layer and will remove all the functionalities written previously on that button.

I used the below code to resolve the same.


Client-side, Typically, the types of things you do in the onModuleLoad() method are: the button; the handler pops up an Alert dialog; the button is added to the Root panel. One way StockWatcher users can enter a stock code is by using their mouse to click on the Add button. You’ll handle the Add button’s click event by passing it an object that implements the ClickHandler interface. In this case, you’ll use an anonymous inner class to implement ClickHandler.

Root Panel Widgets, Reference. The RootPanel is the basis for attaching any GXT widget to the DOM. Find the div id in the HTML and use it with RootPanel.get("divId") for embedding the GXT widget. There is no advantage to using RootLayoutPanel instead of RootPanel when you are using a Viewport� REFERENCE GUIDE CONGRATULATIONS ON YOUR NEW RV PURCHASE! has compiled this guide with the hope that it provides you with some essential information regarding your RV and the Service Center. This is a generalized guide for RVs. This guide is not unit- or brand-specific. Please refer to your owner’s manual for specific details regarding your RV.

gwt - GWT:如何从RootPanel中获得对按钮的引用?, GWT: How do I get a reference to a button from the RootPanel?. I'm using GWT 2.4. In my onModuleLoad method, given a string id, how do I get a reference to� GWT widgets rely on cascading style sheets (CSS) for visual styling. By default, the class name for each component is gwt-<classname>. For example, the Button widget has a default style of gwt-Button and similar way TextBox widgest has a default style of gwt-TextBox. In order to give all buttons and

GWT - Tutorial, Unfortunately the Google Plugin does not allow to create a new Web Button; import; import RootPanel; public class HelloGwt implements EntryPoint { @Override public void The Google Plugin created also a web.xml and placed a reference to a servlet � Now when the user clicks the back button from the “Add Contact” view, GWT’s History mechanism will call the onValueChange() method with the previous history token. In our example the previous view was the “Contact List” view and the previous history token (which was set in the go() method) is “list”.

  • Could you demonstrate how to do this? I have tried the iterator approach (in my edit), but it is not finding an element whose id is definitely on the page.