JFace TableViewer Sorting using LabelProvider

While designing some code for an Eclipse plugin, I decided that I wanted to be able to provide the normal sort mechanism for the tables that is present in so many other applications. I was actually surprised to find that there wasn't a simple API to just turn this on. I sure there are good reasons for this and there are many bug reports in this area. It even looks like there are some fixes in progress.
Anyway, while looking at some examples, I came across this snippet by Tom Schindl. It was really close to what I was looking for, but didn't quite work because it assumed a simple model and didn't exercise the LabelProvider to get the text to sort.

Since I usually create the columns in a loop, it was easy to modify the compare method to look up the index of the column using a label provider.

int i = 0;
for (String name : colNames) {
 final int colIdx = i;
 TableColumn column = new TableColumn(viewer.getTable(), SWT.NONE);
 column.setWidth(200);
 column.setText(name);
 column.setMoveable(true);

 TableColumnSorter cSorter = new TableColumnSorter(viewer, column) {
         protected int doCompare(Viewer v, Object e1, Object e2) {
                 ITableLabelProvider lp = ((ITableLabelProvider) viewer
                 .getLabelProvider());
                 String t1 = lp.getColumnText(e1, colIdx);
                 String t2 = lp.getColumnText(e2, colIdx);
                 return t1.compareTo(t2);
         }
 };

 cSorter.setSorter(cSorter, TableColumnSorter.ASC);
 i++;
}

The full text of the example with my changes are below the split.

package snippet;

/*******************************************************************************
* TableViewerSorting Example
*
* Adam Cabler
*
* revised example by Tom Schindl
* http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.jface.snippets/Eclipse%20JFace%20Snippets/org/eclipse/jface/snippets/viewers/Snippet040TableViewerSorting.java?view=markup
*
* removed ColumnViewer references
* added ITableLabelProvider
* used label provider for text compare
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
*
*******************************************************************************/

import org.eclipse.jface.viewers.ILabelProviderListener;
import org.eclipse.jface.viewers.IStructuredContentProvider;
import org.eclipse.jface.viewers.ITableLabelProvider;
import org.eclipse.jface.viewers.TableViewer;
import org.eclipse.jface.viewers.Viewer;
import org.eclipse.jface.viewers.ViewerComparator;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.TableColumn;

/**
* Table sorting example using label provider
*
* @author cabler
*
*/
public class TableViewerSortingExample {

  private class MyContentProvider implements IStructuredContentProvider {

          public Object[] getElements(Object inputElement) {
                  return (Person[]) inputElement;
          }

          public void dispose() {
          }

          public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
          }
  }

  private class MyLabelProvider implements ITableLabelProvider {

          @Override
          public Image getColumnImage(Object element, int columnIndex) {
                  // TODO Auto-generated method stub
                  return null;
          }

          @Override
          public String getColumnText(Object element, int columnIndex) {
                  if (!(element instanceof Person)) {
                          return null;
                  }
                  Person p = (Person) element;
                  switch (columnIndex) {
                          case 0:
                          return p.givenname;
                          case 1:
                          return p.surname;
                          case 2:
                          return p.email;
                  }
                  return "Error";
          }

          @Override
          public void addListener(ILabelProviderListener listener) {
                  // TODO Auto-generated method stub

          }

          @Override
          public void dispose() {
                  // TODO Auto-generated method stub

          }

          @Override
          public boolean isLabelProperty(Object element, String property) {
                  // TODO Auto-generated method stub
                  return false;
          }

          @Override
          public void removeListener(ILabelProviderListener listener) {
                  // TODO Auto-generated method stub

          }

  }

  public class Person {
          public String givenname;
          public String surname;
          public String email;

          public Person(String givenname, String surname, String email) {
                  this.givenname = givenname;
                  this.surname = surname;
                  this.email = email;
          }

  }

  public TableViewerSortingExample(Shell shell) {
          final TableViewer viewer = new TableViewer(shell, SWT.BORDER | SWT.FULL_SELECTION);
          viewer.setContentProvider(new MyContentProvider());
          viewer.setLabelProvider(new MyLabelProvider());
          String[] colNames = new String[] { "Givenname", "Surname", "Email" };

          int i = 0;
          for (String name : colNames) {
                  final int colIdx = i;
                  TableColumn column = new TableColumn(viewer.getTable(), SWT.NONE);
                  column.setWidth(200);
                  column.setText(name);
                  column.setMoveable(true);

                  TableColumnSorter cSorter = new TableColumnSorter(viewer, column) {
                          protected int doCompare(Viewer v, Object e1, Object e2) {
                                  ITableLabelProvider lp = ((ITableLabelProvider) viewer
                                  .getLabelProvider());
                                  String t1 = lp.getColumnText(e1, colIdx);
                                  String t2 = lp.getColumnText(e2, colIdx);
                                  return t1.compareTo(t2);
                          }
                  };

                  cSorter.setSorter(cSorter, TableColumnSorter.ASC);
                  i++;
          }

          Person[] model = createModel();
          viewer.setInput(model);
          viewer.getTable().setLinesVisible(true);
          viewer.getTable().setHeaderVisible(true);

  }

  private Person[] createModel() {
          Person[] elements = new Person[4];
          elements[0] = new Person("Tom", "Schindl",
          "tom.schindl@bestsolution.at");
          elements[1] = new Person("Boris", "Bokowski",
          "Boris_Bokowski@ca.ibm.com");
          elements[2] = new Person("Tod", "Creasey", "Tod_Creasey@ca.ibm.com");
          elements[3] = new Person("Wayne", "Beaton", "wayne@eclipse.org");

          return elements;
  }

  private static abstract class TableColumnSorter extends ViewerComparator {
          public static final int ASC = 1;

          public static final int NONE = 0;

          public static final int DESC = -1;

          private int direction = 0;

          private TableColumn column;

          private TableViewer viewer;

          public TableColumnSorter(TableViewer viewer, TableColumn column) {
                  this.column = column;
                  this.viewer = viewer;
                  this.column.addSelectionListener(new SelectionAdapter() {

                          public void widgetSelected(SelectionEvent e) {
                                  if (TableColumnSorter.this.viewer.getComparator() != null) {
                                          if (TableColumnSorter.this.viewer.getComparator() == TableColumnSorter.this) {
                                                  int tdirection = TableColumnSorter.this.direction;

                                                  if (tdirection == ASC) {
                                                          setSorter(TableColumnSorter.this, DESC);
                                                  } else if (tdirection == DESC) {
                                                          setSorter(TableColumnSorter.this, NONE);
                                                  }
                                          } else {
                                                  setSorter(TableColumnSorter.this, ASC);
                                          }
                                  } else {
                                          setSorter(TableColumnSorter.this, ASC);
                                  }
                          }
                  });
          }

          public void setSorter(TableColumnSorter sorter, int direction) {
                  if (direction == NONE) {
                          column.getParent().setSortColumn(null);
                          column.getParent().setSortDirection(SWT.NONE);
                          viewer.setComparator(null);
                  } else {
                          column.getParent().setSortColumn(column);
                          sorter.direction = direction;

                          if (direction == ASC) {
                                  column.getParent().setSortDirection(SWT.DOWN);
                          } else {
                                  column.getParent().setSortDirection(SWT.UP);
                          }

                          if (viewer.getComparator() == sorter) {
                                  viewer.refresh();
                          } else {
                                  viewer.setComparator(sorter);
                          }

                  }
          }

          public int compare(Viewer viewer, Object e1, Object e2) {
                  return direction * doCompare(viewer, e1, e2);
          }

          protected abstract int doCompare(Viewer TableViewer, Object e1, Object e2);
  }

  /**
  * @param args
  */
  public static void main(String[] args) {
          Display display = new Display();

          Shell shell = new Shell(display);
          shell.setLayout(new FillLayout());
          new TableViewerSortingExample(shell);
          shell.open();

          while (!shell.isDisposed()) {
                  if (!display.readAndDispatch())
                  display.sleep();
          }

          display.dispose();

  }

}