Remove a generated panel in GWT after a button is clicked

Question

I am attempting to create a Google Web Toolkit (GWT) application that also uses Google Gears, but every time I try to remove the panel, I get an exception and the panel stays there.

Here is an excerpt from the exception I get (I've only included the relevant bits of the call stack, the rest just descends into the included function below):

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:122)
 at com.google.gwt.user.client.ui.RootPanel.get(RootPanel.java:197)

I'm not sure what the problem is, but I really don't like leaving the button there after they approve the use of Gears.

What am I doing wrong? Or any suggestions on a different way I could do this to make it work?

if(!gearsFactory.hasPermission()) {
 HorizontalPanel rightPanel = new HorizontalPanel();
 rightPanel.getElement().setId("gearsPrompt");
 rightPanel.setVerticalAlignment(HorizontalPanel.ALIGN_MIDDLE);
 rightPanel.setSpacing(0);
 rightPanel.setHeight("28px");

 InlineLabel enableGearsText = new InlineLabel("Enable Gears for off-line access");
 enableGearsText.getElement().setId("gearsText");
 enableGearsText.addStyleName("titleElement");
 rightPanel.add(enableGearsText);

 final Button gearsButton = new Button("Use Gears");
 gearsButton.getElement().setId("gearsButton");
 gearsButton.addStyleName("titleElement");
 gearsButton.setHeight("24px");

 gearsButton.addClickHandler( new ClickHandler() {
  public void onClick(ClickEvent event) {
   Factory gearsFactory = Factory.getInstance();
   if(gearsFactory != null) {
    if(gearsFactory.getPermission()) {
     RootPanel gearsPrompt = RootPanel.get("gearsPrompt");
     gearsPrompt.removeFromParent();
    }
   }
  }
 });

 rightPanel.add(gearsButton);

 RootPanel titleBarRight = RootPanel.get("titleBarRight");
 titleBarRight.add(rightPanel);
}

Answer 1

One solution I've found is to loop through all of the widgets under the "titleBarRight" panel and remove all widgets it contains:

if(gearsFactory.getPermission()) {
 RootPanel titleBarRight = RootPanel.get("titleBarRight");
 java.util.Iterator<Widget> itr = titleBarRight.iterator();
 while(itr.hasNext()) {
  itr.next();
  itr.remove();
 }
}

But somehow this still seems hacky and not quite the "right way to do it."

Answer 2

Is there any reason for using RootPanel.get("gearsPrompt").removeFromParent(); instead of your own rightPanel.removeFromParent();? The reference is already there.

Answer 3

You can do :

theParentWidget.remove(index);

and the first child corresponds to 0;