Can not see table items in SWT Table

Question

I am trying to create the following dialog:

I have tried this:

import java.util.HashSet;
import java.util.Set;

import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Dialog;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Spinner;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableColumn;
import org.eclipse.swt.widgets.TableItem;

public class CorrelationDlg extends Dialog {
    private final GridLayout composite;
    private Spinner spinner;
    private Button button;
    private final Table ancestors;
    private final Table descendants;

    public CorrelationDlg(Shell shell) {
        super(shell);
        composite = new GridLayout(4, false);
        shell.setLayout(composite);

        spinner = new Spinner(shell, SWT.FILL);
        spinner.setMinimum(0);
        spinner.setMaximum(7);
        spinner.setIncrement(1);

        GridData spinnerData = new GridData(SWT.FILL, SWT.BEGINNING, true, false);
        spinnerData.horizontalSpan = 3;
        spinner.setLayoutData(spinnerData);
        spinner.pack();

        button = new Button(shell, SWT.CHECK);
        button.setText("Self:");
        GridData buttonData = new GridData(SWT.FILL, SWT.BEGINNING, true, false);
        buttonData.horizontalSpan = 3;
        button.setLayoutData(buttonData);
        button.pack();

        ancestors = new Table(shell, SWT.CHECK | SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL);
        final TableColumn ancestorsColumn = new TableColumn(ancestors, SWT.NONE);
        ancestorsColumn .setText("Ancestors");
        ancestors.setHeaderVisible(true);
        GridData ancestorsData = new GridData(GridData.FILL_BOTH, SWT.BEGINNING, true, false);
        ancestorsData.horizontalSpan = 3;
        ancestors.setLayoutData(ancestorsData);

        descendants = new Table(shell, SWT.CHECK | SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL);
        final TableColumn descendantsColumn = new TableColumn(descendants, SWT.NONE);
        descendantsColumn.setText("Descendants");
        descendants.setHeaderVisible(true);
        GridData descendantsData = new GridData(GridData.FILL_BOTH, SWT.BEGINNING, true, false);
        descendantsData.horizontalSpan = 1;
        descendants.setLayoutData(descendantsData);
    }

    public void addAncestors(Set<String> resourceKinds) {
        for(final String resourceKind: resourceKinds) {
            final TableItem item = new TableItem(ancestors, SWT.NONE);
            item.setText(resourceKind);
        }
        ancestors.pack();
    }

    public void addDescendants(Set<String> resourceKinds) {
        for(final String resourceKind: resourceKinds) {
            final TableItem item = new TableItem(descendants, SWT.NONE);
            item.setText(resourceKind);
        }
        descendants.pack();
    }

    public static void main(String[] args) {
          Display display = new Display();
          Shell shell = new Shell(display);

          CorrelationDlg dlg = new CorrelationDlg(shell);
          Set<String> ancestors = new HashSet<>();
          ancestors.add("A1");
          ancestors.add("A2");
          dlg.addAncestors(ancestors);

          Set<String> ds = new HashSet<>();
          ds.add("A1");
          ds.add("A2");
          dlg.addDescendants(ds);

          shell.setSize(200, 200);
          shell.pack();
            shell.open();
            while (!shell.isDisposed()) {
              if (!display.readAndDispatch())
                display.sleep();
            }
            display.dispose();
          }
}

But currently I am unable to see table items. Could you please point out what is the problem with this?

Answer 1

You didn't set the columns width and didn't correctly pack() them, so their width is 0.

You can set the width using setWidth, for example:

ancestorsColumn.setWidth(100);

or "pack" them with their pack() method, for example in addAncestor you could add this:

ancestors.getColumn(0).pack();

Answer 2

Your TableItems are definitely being added, which you can see if you resize the column:

What you'll need to do is either specify a width for the column via TableColumn#setWidth(int) or via a TableLayout (and potentially also TableColumnLayout if your table will be resized, as this layout will maintain proportions per the documentation).