Move ViewPort of Element Map in GWT?

Question

I have a GWT application with a viewport that shows a part of an element map. On the element map are div elements. The user can drag and move on the viewport (not on the elements). If the user drag and move on the viewport than he can move the viewport to all directions. This means that another part of the element map will be displayed. The browser position of the viewport remains unchanged, only the element map moves on drap and move of the viewport.

How do I have to setup the viewport and the element map to make it drag and move ready?

Answer 1

Place the widget by using method setWidgetPosition. To move a views within the viewport, updated them position -

public class Viewport extends AbsolutePanel {
  private static final String DEFAULT_MOUSE_DOWN_CURSOR = "moveCursor";
  private static final String DEFAULT_MOUSE_DRAG_CURSOR = "pointerCursor";

  private final FocusPanel panel = new FocusPanel();

  private String mouseDownCursor = DEFAULT_MOUSE_DOWN_CURSOR;
  private String mouseDragCursor = DEFAULT_MOUSE_DRAG_CURSOR;

  private Widget view = null;

  private boolean dragging = false;
  private int xOffset, yOffset;

  private boolean eventPreviewAdded = false;

  private static EventPreview preventDefaultMouseEvents = new EventPreview() {
      public boolean onEventPreview(Event event) {
        switch (DOM.eventGetType(event)) {
           case Event.ONMOUSEDOWN:
           case Event.ONMOUSEMOVE:
             DOM.eventPreventDefault(event);
        }
        return true;
      }
    };

  public Viewport() {
    add(panel);

    panel.addMouseListener(new MouseListenerAdapter() {
      public void onMouseEnter() {
       DOM.addEventPreview(preventDefaultMouseEvents);
      }

      public void onMouseLeave() {
       DOM.removeEventPreview(preventDefaultMouseEvents);
      }

      public void onMouseDown(Widget widget, int x, int y) {
        dragging = true;

        xOffset = x;
        yOffset = y;

        DOM.setCapture(panel.getElement());
      }

      public void onMouseMove(Widget widget, int x, int y) {
        if (dragging) {
          removeStyleName(mouseDownCursor);
          addStyleName(mouseDragCursor);

          int newX = x + getWidgetLeft(panel) - xOffset;
          int newY = y + getWidgetTop(panel) - yOffset;

          setWidgetPosition(panel, newX, newY);
        }
      }

      public void onMouseUp(Widget widget, int x, int y) {
        if (dragging) {
          dragging = false;
          removeStyleName(mouseDownCursor);
          removeStyleName(mouseDragCursor);

          DOM.releaseCapture(panel.getElement());
        }
      }
    });
  }

  public String getMouseDownCursor() {
    return mouseDownCursor;
  }

  public void setMouseDownCursor(String mouseDownCursor) {
    this.mouseDownCursor = mouseDownCursor;
  }

  public String getMouseDragCursor() {
    return mouseDragCursor;
  }

  public void setMouseDragCursor(String mouseDragCursor) {
   this.mouseDragCursor  = mouseDragCursor;
  }

 public Widget getView() {
  return view;
 }

 public void setView(Widget view) {
   this.view = view;
   panel.setWidget(view);
 }
}

See Google Web Toolkit Solutions: More Cool & Useful Stuff

---

More examples -

• Solution 4. Viewports and Maps
• http://www.salvin.in/
• GWT Canvas Demo

Look at this book, which I recommend to you. There are step by step instructions for what you want to do.

Answer 2

Maybe you need a widget to scroll in any direction using drag or tap events.

The mgwt library has a ScrollPanel ready for this, take a look to their example.

[Edited] Example using mgwt

import com.googlecode.mgwt.ui.client.widget.LayoutPanel;
import com.googlecode.mgwt.ui.client.widget.RoundPanel;
import com.googlecode.mgwt.ui.client.widget.ScrollPanel;

public void onModuleLoad() {

  // You need to use both widgets mgwt-LayoutPanel and mgwt-ScrollPanel:
  LayoutPanel main = new LayoutPanel();
  ScrollPanel scrollPanel = new ScrollPanel();

  // This is optional, you can use any gwt-Panel instead
  RoundPanel roundPanel = new RoundPanel();

  scrollPanel.setWidget(roundPanel);
  main.add(scrollPanel);
  RootPanel.get().add(main);


  StringBuffer buffer = new StringBuffer();
  for (int i = 0; i < 500; i++) {
      buffer.append("Lorem ipsum dolor sit amet, consectetur adipiscing elit");
  }
  HTML html = new HTML(buffer.toString());

  roundPanel.add(html);

  // Set the size of your view-port and its content
  main.setSize("400px", "400px");
  html.setWidth("1000px");

}

You have to include mgwt library in your classpath and set these lines in your .gwt.xml file:

<inherits name="com.googlecode.mgwt.MGWTMin"/>
<set-property name="mgwt.os" value="desktop" />
<set-property name="mobile.user.agent" value="not_mobile" />