Widget Updating Content Of Another Panel

I have a page layout that contains a static header / footer, and 2 dynamic portions (an action bar, and a scrollable content area).  

I want my resulting page to resemble:

---HEADER--- (static)

---action-bar--- (dynamic, updated by whatever is in Content)

---content--- (dynamic, scrollable)

---FOOTER--- (static)

I have setup my main page layout like this:

AppTemplateView.java:

    ...

    ActionBar actionBar = new ActionBar();

    ...

    DockLayoutPanel masterLayout = new DockLayoutPanel(Unit.PX);                

    masterLayout.addNorth(buildHeaderPanel(), 53);

    masterLayout.addNorth(actionBar, 48);

    masterLayout.addSouth(buildFooterPanel(), 32); 

    ScrollPanel scrollPanel = new ScrollPanel();

    scrollPanel.add(appPanel);

    masterLayout.add(scrollPanel);     

    initWidget(masterLayout);    

    ...

    public void setActionBar(ActionBar newActionBar) {

        this.actionBar = newActionBar;  // What do I actually need to do here???

    }

I'm using native GWT no extensions.  My app uses Activities and Places.  Initially the screen renders fine, but when I navigate to a different view, the content area updates correctly, but the action-bar doesn't change.  I'd like to update the action-bar from within each view dynamically.  For example:

TestView.java:

  public TestView(AppTemplateView template) {

    

    ActionBar actionBar = new ActionBar();

    // build up the custom action bar for this view.   Add it to the template

    template.setActionBar(actionBar);    

    

    // and build up the actual content for this view. 

    VerticalPanel container = new VerticalPanel();

    container.add(new Label("Content goes here..."));

    initWidget(container);

  }

What's the right way to replace the actionBar content in the template from within one of my views?  I've tried having actionBar in the template be a SimplePanel, and from my setActionBar() method calling actionBar.clear(); actionBar.add(newActionBar); but it still didn't update in the browser. 

Another way I thought was to call from within setActionBar(ActionBar newActionBar):

   Element el = masterLayout.getWidgetContainerElement(actionBar);

   el.removeAllChildren();

   el.appendChild(newActionBar);

   this.actionBar = newActionBar;

But I'm not sure if that's even a valid approach.

Any suggestions?

Nick

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