SWT: Trees

Trees are used to display information in hierarchical format. You can get notifications when an item in the hierarchy is selected.

Following styles are used while creating Tree instance.

Style	Description
SINGLE	Style constant for single selection behavior. You can able to select only one item in the tree at a time.
MULTI	Style constant for multi-selection behavior.  You can able to select multiple items in the tree.
CHECK	Style constant for check box behavior.
FULL_SELECTION	Style constant for full row selection behavior.
VIRTUAL	Style constant to allow virtual data. By using this, you can populate tree items on demand basis.
NO_SCROLL	Style constant for no scrollbar behavior.

How to define a tree?

By using Tree constructor, you can define a tree.

Tree tree = new Tree(shell, SWT.MULTI | SWT.BORDER);

tree.setSize(150, 150);

tree.setLocation(5, 5);

How to add an item to hierarchy in the tree?

By using TreeItem class, you can add an item to tree hierarchy. TreeItem class provides following constructors to define a TreeItem instance.

Following two constructors are used to attach TreeItem to a tree.

public TreeItem (Tree parent, int style)

public TreeItem (Tree parent, int style, int index)

Following two constructors are used to attach a TreeItem to another TreeItem.

public TreeItem (TreeItem parentItem, int style)

public TreeItem (TreeItem parentItem, int style, int index)

You can also add an image to TreeItem. Following statements adds an image to TreeItem.

Image icon = new Image(display, "help.bmp");

TreeItem item = new TreeItem(tree, SWT.NONE);

item.setImage(icon);

By using SelectionListener, you can able to get all the TreeItems selected in the tree.

tree.addSelectionListener(new SelectionAdapter() {

         public void widgetSelected(SelectionEvent e) {

                 TreeItem[] selectedItems = tree.getSelection();

                 System.out.print("Selected Items: ");

                 for (int i = 0; i < selectedItems.length; i++) {

                          System.out.print(selectedItems[i].getText() + ", ");

                 }

                 System.out.println();

         }

});

Get the TreeItem expansion and collapsed status

By using TreeListener interface, you can get notification, whenever the tree item is collapsed (or) expanded.

TreeListener interface provides following methods.

Method	Description
public void treeCollapsed(TreeEvent e)	Notify when a tree branch is collapsed.
public void treeExpanded(TreeEvent e)	Notify when a tree branch is expanded.

Following is the complete working application.

package swt_app;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.events.TreeEvent;
import org.eclipse.swt.events.TreeListener;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Tree;
import org.eclipse.swt.widgets.TreeItem;

public class Test {

 private static int shellWidth = 1000;
 private static int shellHeight = 700;

 private static void addWidgetsToShell(Display display, Shell shell) {
  Tree tree = new Tree(shell, SWT.MULTI | SWT.BORDER);

  tree.setSize(150, 150);
  tree.setLocation(5, 5);

  TreeItem child1 = new TreeItem(tree, SWT.NONE);
  child1.setText("child1");

  TreeItem child3 = new TreeItem(tree, SWT.NONE);
  child3.setText("child3");

  TreeItem child2 = new TreeItem(tree, SWT.NONE, 1);
  child2.setText("child2");

  TreeItem child2_1 = new TreeItem(child2, SWT.NONE);
  child2_1.setText("child2_1");

  TreeItem child2_2 = new TreeItem(child2, SWT.NONE);
  child2_2.setText("child2_2");

  tree.addSelectionListener(new SelectionAdapter() {
   public void widgetSelected(SelectionEvent e) {
    TreeItem[] selectedItems = tree.getSelection();
    System.out.print("Selected Items: ");
    for (int i = 0; i < selectedItems.length; i++) {
     System.out.print(selectedItems[i].getText() + ", ");
    }
    System.out.println();
   }
  });

  tree.addTreeListener(new TreeListener() {
   public void treeCollapsed(TreeEvent e) {
    System.out.println("Tree collapsed.");
   }

   public void treeExpanded(TreeEvent e) {
    System.out.println("Tree expanded.");
   }
  });
 }

 public static void main(String[] args) {

  /* Instantiate Display object, it represents SWT session */
  Display display = new Display();

  /*
   * Define Shell, it represent a window, You can add more than one shell
   * to Display
   */
  Shell shell = new Shell(display);
  shell.setSize(shellWidth, shellHeight);
  shell.setText("SWT Tutorial");

  addWidgetsToShell(display, shell);

  /* Open shell window */
  shell.open();

  /*
   * Run the event dispatching loop until an exit condition occurs, which
   * is typically when the main shell window is closed by the user.
   */

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

  /* Dispose the display */
  display.dispose();

 }
}

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