Exception while adding a widget to iframe?

Question

I am using GWT. have below code in my host page.

<div id="mainDiv"/>
 <iframe id="__printingFrame" style="width:0;height:0;border:0"> </iframe> 

in EntryPoint's onModuleLoad() i have below code:

@Override
    public void onModuleLoad() {
        RootPanel.get("mainDiv").add(new SomePage());
    }

in one of the methods of SomePage.java i am doing:

RootPanel rootPanel = RootPanel.get("__printingFrame");
  rootPanel.add(new Html(" "));//adding some widget

But bcaz of above line i am getting below exception. Am i missing anything here?

java.lang.AssertionError: A widget that has an existing parent widget may not be added to the detach list
    at com.google.gwt.user.client.ui.RootPanel.detachOnWindowClose(RootPanel.java:136)
    at com.google.gwt.user.client.ui.RootPanel.get(RootPanel.java:211)

Thanks!

Answer 1

There are 2 issues in your code (but you're only seeing one for now):

• You cannot have nested RootPanels (see http://code.google.com/p/google-web-toolkit/issues/detail?id=3511 and http://code.google.com/p/google-web-toolkit/issues/detail?id=3528), this is what's causing the error you're seeing

• You cannot add widgets to an iframe. Well, wrapping it within a RootPanel, technically, you could, but they'd be added as children of the iframe element, so they wouldn't be visible to your users (I cannot think of a single browser that interprets JavaScript but doesn't support iframes).

Answer 2

RootPanel.get("id") can only get <div> element.you can wrap existed element like that.

Frame frame=Frame.wrap(DOM.getElementById("__printingFrame"));