How would I use GWT to create an infinite scroll panel

Question

By infinite scrolling, I mean I initially load a few child widgets, and as the user scrolls down lazily load more to fill it out.

Any ideas appreciated.

(ideally would like something for GWT 1.6 and 1.5)

Answer 1

Hi, try something like this:

public static class InfiniteScrollPanel implements ScrollHandler {
 String text="Lorem ipsum dolor sit amet, consectetuer...";
 ScrollPanel panel=new ScrollPanel(new HTML(text));
 int height=200;
 int width=200;

 public InfiniteScrollPanel() {
  panel.setHeight(height);
  panel.setWidth(width);
  panel.addScrollHandler(this);   
 }
 public void onScroll(ScrollEvent event) {
  if(panel.getScrollPosition==height) {
    panel.add(new HTML(text));
  }
 }
}

What this code does: it creates a ScrollPanel and adds a ScrollHandler to it. In the ScrollHandler the scrollheight gets compared to the height of the panel and it then adds another child to the panel.

I haven't tested it because I'm wtriting this on a netbook and don't have an IDE on it.

Hope that helps Chris

Answer 2

I was able to confirm the following works in GWT 1.5 at least:

        final VerticalPanel vp = new VerticalPanel();
    for (int i = 0; i < 40; i++) {
        vp.add(new HTML("Oh oh"));
    }
    final HTML f = new HTML("END");
    vp.add(f);

    final ScrollPanel panel = new ScrollPanel(vp);
    panel.setHeight("20em");
    panel.addScrollListener(new ScrollListener() {

        HTML end = f;
        public void onScroll(Widget widget, int scrollLeft, int scrollTop) {


            int finalPos = end.getAbsoluteTop() + end.getOffsetHeight(); 
            int panelPos = panel.getAbsoluteTop() + panel.getOffsetHeight();
            if (finalPos == panelPos) {
                end = new HTML("MORE !!");
                vp.add(end);
            }


        }
    });

Note the interesting bits are the calculations of the positions.