Inspired by a bugzilla-discussion where virtual support for the nebula grid. I thought I blog a bit about Eclipse Databinding when it comes to big datasets.

The standard way used looks like this:

IObservable list = // ... a huge list of items

TableViewer viewer = new TableViewer(parent,SWT.BORDER|SWT.H_SCROLL|SWT.V_SCROLL);
ObservableListContentProvider cp = new ObservableListContentProvider();
viewer.setContentProvider(cp);

TableViewerColumn column = new TableViewerColumn(viewer,SWT.NONE);
column.getColumn().setText("Firstname");
column.getColumn().setWidth(200);
column.setLabelProvider(new ObservableMapCellLabelProvider(
    BeanProperties.value("firstname").observeDetail(cp.getKnownElements())
  )
);

TableViewerColumn column = new TableViewerColumn(viewer,SWT.NONE);
column.getColumn().setText("Lastname");
column.getColumn().setWidth(200);
column.setLabelProvider(new ObservableMapCellLabelProvider(
    BeanProperties.value("lastname").observeDetail(cp.getKnownElements())
  )
);

viewer.setInput(list);

Executing this code with the following item count shows the following figures:

So as we might have guess the performance degrades with the number of items with put in the viewer. In SWT you normally get the advise to use SWT.VIRTUAL but I don’t think that will address all your problems. One of them is the freaking high number of Listeners attached to your domain-objects. For 200.000 items above Eclipse Databinding has created 400.000 listeners (200.000 rows x 2 columns) not think about what would have happened if you’d have 10 columns.

So in reality there are 2 problems we have to address:

• get the time of the initial creation down
• only attach listeners only to those elements visible in the viewer

As outlined for SWT-Table you could address the 1st problem using SWT.VIRTUAL but for the 2nd there’s no solution. For Nebula-Grid the situation is different you don’t have SWT.VIRTUAL but instead of that some much more powerful. You can attach a listener and get informed about all visible cells so we can address both problems.

Let’s first look at the figures:

So the numbers have improved dramatically but the other really nice thing is that because by viewer shows in my test e.g. only 24 rows I have a total of 48 listeners attached to my domain objects.

The code is not really complex:

public class ViewOptimized extends ViewPart {
  public static final String ID = "at.bestsolution.grid.databinding.view";

  private GridTableViewer viewer;
	
  static final String ITEM_VISIBLE = "ITEM_VISIBLE";
	
  private static int LISTENERCOUNT = 0;
	
  public static class Person {
    private PropertyChangeSupport support = new PropertyChangeSupport(this);
		
    private String firstName;
    private String lastName;
		
    public void addPropertyChangeListener(PropertyChangeListener listener) {
      support.addPropertyChangeListener(listener);
      LISTENERCOUNT++;
    }
		
    public void removePropertyChangeListener(PropertyChangeListener listener) {
      support.removePropertyChangeListener(listener);
      LISTENERCOUNT--;
    }

    public Person(String firstName, String lastname) {
      this.firstName = firstName;
      this.lastName = lastname;
    }
		
    public String getFirstName() {
      return firstName;
    }

    public void setFirstName(String firstName) {
      support.firePropertyChange("firstName", this.firstName, 
        this.firstName = firstName
      );
    }
		
    public String getLastName() {
      return lastName;
    }

    public void setLastName(String lastName) {
      support.firePropertyChange("lastName", this.lastName, 
        this.lastName = lastName
      );
    }
  }

  public void createPartControl(Composite parent) {
    parent.setLayout(new GridLayout());
    this.viewer = new GridTableViewer(parent);
    this.viewer.getGrid().setHeaderVisible(true);
    this.viewer.getGrid().setLayoutData(new GridData(GridData.FILL_BOTH));
		
    viewer.setContentProvider(new ObservableListContentProvider());
    ObservableSet obserableSet = new WritableSet();
		
    GridVisibleRangeSupport rangeSupport = 
      GridVisibleRangeSupport.createFor(viewer.getGrid());
    rangeSupport.addRangeChangeListener(
      new VisibleRangeListenerImpl(viewer,obserableSet)
    );
		
    {
      GridViewerColumn col = new GridViewerColumn(viewer, SWT.NONE);
      col.getColumn().setText("Firstname");
      col.getColumn().setWidth(200);
      col.setLabelProvider(new LazyColumnLabelProvider(
        BeanProperties.value("firstName").observeDetail(obserableSet))
      );
    }
		
    {
      GridViewerColumn col = new GridViewerColumn(viewer, SWT.NONE);
      col.getColumn().setText("Lastname");
      col.getColumn().setWidth(200);
      col.setLabelProvider(new LazyColumnLabelProvider(
        BeanProperties.value("lastName").observeDetail(obserableSet))
      );
    }

    final ObservableList list = new WritableList();
    for( int i = 0; i < ViewOriginal.TOTAL_ITEMS; i++ ) {
      list.add(new Person("Tom " + i,"Schindl"));
    }
		
    Composite composite = new Composite(parent, SWT.NONE);
    composite.setLayout(new RowLayout());
		
    {
      Button b = new Button(composite, SWT.PUSH);
      b.setText("Populate it");
      b.addSelectionListener(new SelectionAdapter() {
        @Override
        public void widgetSelected(SelectionEvent e) {
          long t1 = System.currentTimeMillis();
          viewer.setInput(list);
          long t2 = System.currentTimeMillis();
          System.err.println("Rendering table took: " + (t2 - t1));
        }
      });
    }
		
    {
      Button b = new Button(composite, SWT.PUSH);
      b.setText("Modify First Object");
      b.addSelectionListener(new SelectionAdapter() {
        @Override
        public void widgetSelected(SelectionEvent e) {
          ((Person)list.get(0)).setFirstName("Hello World");
        }
      });
    }

    {
      Button b = new Button(composite, SWT.PUSH);
      b.setText("Stats");
      b.addSelectionListener(new SelectionAdapter() {
        @Override
        public void widgetSelected(SelectionEvent e) {
          System.err.println("Listeners: " + LISTENERCOUNT);
        }
      });
    }
  }

  public void setFocus() {
    viewer.getControl().setFocus();
  }

  public static class LazyColumnLabelProvider extends 
    ObservableMapCellLabelProvider {

    public LazyColumnLabelProvider(IObservableMap attributeMap) {
      super(attributeMap);
    }
		
    @Override
    public void update(ViewerCell cell) {
      Object visibleCheck = cell.getItem().getData(ITEM_VISIBLE);
      if( visibleCheck != null && ((Boolean)visibleCheck).booleanValue() ) {
        super.update(cell);
      }
    }
  }

  public static class VisibleRangeListenerImpl implements 
    VisibleRangeChangedListener {

    private ObservableSet obserableSet;
    private GridTableViewer viewer;
		
    public VisibleRangeListenerImpl(GridTableViewer viewer, 
      ObservableSet obserableSet
    ) {
      this.viewer = viewer;
      this.obserableSet = obserableSet;
    }
		
    @Override
    public void rangeChanged(RangeChangedEvent event) {
      for( GridItem i : event.removedRows ) {
        i.setData(ITEM_VISIBLE,Boolean.FALSE);
        obserableSet.remove(i.getData());
      }
			
      for( GridItem i : event.addedRows ) {
        i.setData(ITEM_VISIBLE,Boolean.TRUE);
        obserableSet.add(i.getData());
        viewer.update(i.getData(), null);
      }
    }	
  }
}

To round up the numbers here are those you get with plain SWT-Table with and without VIRTUAL: