Recipe 10.6 Handling Tree Events

10.6.1 Problem

You need to know when the user selects an item in a tree widget.

10.6.2 Solution

Add a new listener to the Tree widget, using the addListener or addSelectionListener methods.

10.6.3 Discussion

As an example, we'll add a listener to the tree developed in the previous recipe. We'll also add a text widget to display the user's selection, as shown in Example 10-3.

Example 10-3. SWT trees

package org.cookbook.ch10;

import org.eclipse.swt.*;
import org.eclipse.swt.widgets.*;

public class TreeClass
{

    public static void main(String[] args)
    {
        Display display = new Display( );
        Shell shell = new Shell(display);
        shell.setText("Tree Example");

        final Text text = new Text(shell, SWT.BORDER);
        text.setBounds(0, 270, 290, 25);

        final Tree tree = new Tree(shell, SWT.BORDER | SWT.V_SCROLL | 
             SWT.H_SCROLL);
        tree.setSize(290, 260);
        shell.setSize(300, 330);

        for (int loopIndex0 = 0; loopIndex0 < 10; loopIndex0++)
        {
            TreeItem treeItem0 = new TreeItem(tree, 0);
            treeItem0.setText("Level 0 Item " + loopIndex0);
            for (int loopIndex1 = 0; loopIndex1 < 10; loopIndex1++)
            {
                TreeItem treeItem1 = new TreeItem(treeItem0, 0);
                treeItem1.setText("Level 1 Item " + loopIndex1);
                for (int loopIndex2 = 0; loopIndex2 < 10; loopIndex2++)
                {
                    TreeItem treeItem2 = new TreeItem(treeItem1, 0);
                    treeItem2.setText("Level 2 Item " + loopIndex2);
                }
            }
        }

        tree.addListener(SWT.Selection, new Listener( )
        {
            public void handleEvent(Event event)
            {
                text.setText(event.item + " was selected");
            }
        });

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

With the new listener and the text widget to display selection events, the TreeApp example can display selections the user makes, as shown in Figure 10-5.

Figure 10-5. Catching tree selection events

10.6.4 See Also

Recipe 10.5 on creating SWT trees; Recipe 10.7 on adding checkboxes to tree items; Recipe 10.8 on adding images to tree items.