Java SWT ScrolledComposite Performance with many Composites inside

Question

i have a problem with my Java SWT ScrolledComposite:

In a (centered) ScrolledComposite are displayed many pictures previews (see picture images). If the images in the ScrolledComposite are loaded, it takes a long time. After that the previews lags on scolling.

Quick: it has a really poor performance. So my idea: i calculate the scoll bar and load only the displayed pictures. If the user scoll down, it will be load the other pictures.

My (test) code:

    Composite center = new Composite(form, SWT.NONE);
    center.setLayout(new FillLayout());

    ScrolledComposite centerScrolledComposite = new ScrolledComposite(center, SWT.V_SCROLL | SWT.BORDER);

    Display display = getDisplay();
    Image image1 = display.getSystemImage(SWT.ICON_WORKING);
    Image image2 = display.getSystemImage(SWT.ICON_QUESTION);
    Image image3 = display.getSystemImage(SWT.ICON_ERROR);


    Composite wrappedScrolledComposite = new Composite(centerScrolledComposite, SWT.NONE);
    for (int i = 0; i <= 5000; i++)
    {
        Label label = new Label(wrappedScrolledComposite, SWT.NONE);
        if (i % 3 == 0)
            label.setImage(image1);
        if (i % 3 == 1)
            label.setImage(image2);
        if (i % 3 == 2)
            label.setImage(image3);
    }
    
    RowLayout layout = new RowLayout(SWT.HORIZONTAL);
    layout.wrap = true;
    wrappedScrolledComposite.setLayout(layout);

    centerScrolledComposite.setContent(wrappedScrolledComposite);
    centerScrolledComposite.setExpandHorizontal(true);
    centerScrolledComposite.setExpandVertical(true);
    centerScrolledComposite.addControlListener(new ControlAdapter() {
        public void controlResized(ControlEvent e) {
          Rectangle r = centerScrolledComposite.getClientArea();
          centerScrolledComposite.setMinSize(wrappedScrolledComposite.computeSize(r.width, SWT.DEFAULT));
        }
      });

But.. i don't know if it's possible. Have anybody a similar problem? Thanks

PS: i need a view very simular to the Windows 10 File Browser with "Big Icos" as preview.... and the same performance :)

greg-449 · Answer 1 · 2022-01-26T10:00:01.893

Replace all those labels with a Table or TableViewer - just a single control.

Since tables can scroll themselves you also don't need the ScrolledComposite.

Table table = new Table(form, SWT.V_SCROLL | SWT.H_SCROLL | SWT.SINGLE);

for (int i = 0; i <= 5000; i++)
 {
   TableItem label = new TableItem(table, SWT.NONE);
   if (i % 3 == 0)
     label.setImage(image1);
   if (i % 3 == 1)
     label.setImage(image2);
   if (i % 3 == 2)
     label.setImage(image3);
 }

For even better performance you can make the table "Virtual" and populate the contents as required:

Table table = new Table(composite, SWT.VIRTUAL | SWT.V_SCROLL | SWT.H_SCROLL | SWT.SINGLE);

table.setItemCount(5000);

table.addListener(SWT.SetData, event -> {
      TableItem label = (TableItem)event.item;
      int i = table.indexOf(label);
      if (i % 3 == 0)
        label.setImage(image1);
      if (i % 3 == 1)
        label.setImage(image2);
      if (i % 3 == 2)
        label.setImage(image3);
    });

Thanks, really better with a table instead of ScrolledComposite :) — Todo, Jan 26 '22 at 21:30

Java SWT ScrolledComposite Performance with many Composites inside

1 Answers1