Navigating to a new view with gwt-presenter, part 2

In the previous post, we considered how to switch between views using a DeckPanel. Depending on the situation, one possible disadvantage to a DeckPanel is that it retains each member view widget in memory even when not displayed. If instead you want to remove a view widget from its container when transitioning to another view, you can use gwt-presenter’s WidgetContainerPresenter and WidgetContainerDisplay classes. Here is the same example shown with these classes in which we use a VerticalPanel as a container and navigate from the ManageListsPresenter/View to the AddPrayerListPresenter/View within the VerticalPanel. Note that the ContentContainerPresenter constructor calls showPresenter(). This is very important, as our view’s implementation of showWidget() calls clear() and add() to replace the existing contents of the VerticalPanel with the new widget. If you don’t call showPresenter() in the container constructor, then the default behavior of WidgetContainerPresenter is to add all the member presenters to the view.

package com.roa.client.presenter;

import net.customware.gwt.presenter.client.EventBus;
import net.customware.gwt.presenter.client.place.Place;
import net.customware.gwt.presenter.client.place.PlaceRequest;
import net.customware.gwt.presenter.client.widget.WidgetContainerDisplay;
import net.customware.gwt.presenter.client.widget.WidgetContainerPresenter;
import net.customware.gwt.presenter.client.widget.WidgetPresenter;

public class ContentContainerPresenter extends WidgetContainerPresenter<ContentContainerPresenter.Display>
{

	private static final Place PLACE = new Place("content");

	public interface Display extends WidgetContainerDisplay
	{
	}

	public ContentContainerPresenter(Display display, EventBus eventBus,
			WidgetPresenter<?>[] presenters)
	{
		super(display, eventBus, presenters);
		bind();
		// Show first presenter as default
		showPresenter(presenters[0]);
	}

	@Override
	public Place getPlace()
	{
		return PLACE;
	}

	@Override
	protected void onPlaceRequest(PlaceRequest request)
	{
		// TODO Auto-generated method stub
	}

}

And here is the matching view that uses a VerticalPanel as the container widget:

package com.roa.client.ui.web.content;

import com.google.gwt.user.client.ui.VerticalPanel;
import com.google.gwt.user.client.ui.Widget;
import com.roa.client.presenter.ContentContainerPresenter.Display;

public class ContentContainerView implements Display
{

	private final VerticalPanel contentPanel = new VerticalPanel();

	public ContentContainerView()
	{
	}

	@Override
	public void addWidget(Widget widget)
	{
		contentPanel.add(widget);
	}

	@Override
	public void removeWidget(Widget widget)
	{
		contentPanel.remove(widget);
	}

	@Override
	public void showWidget(Widget widget)
	{
		contentPanel.clear();
		contentPanel.add(widget);
	}

	@Override
	public Widget asWidget()
	{
		return contentPanel;
	}

	@Override
	public void startProcessing()
	{
		// TODO Auto-generated method stub
	}

	@Override
	public void stopProcessing()
	{
		// TODO Auto-generated method stub
	}

}

These are wired up in AppPresenter and the view change triggered with a PlaceRequestEvent just as shown in the previous post.

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