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Swing Chapter 17. (Advanced topics) Trees. Easy for reading, Click here!

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Swing Chapter 17. (Advanced topics) Trees. Easy for reading, Click here!

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Page: 5/7 



Previous Page Previous Page (4/7) - Next Page (6/7) Next Page
Subpages: 1. JTree 
2.
Basic JTree example 
3.
Directories tree: part I - Dynamic node retrieval 
4. Directories tree: part II - Popup menus and programmatic navigation 
5. Directories tree: part III - Tooltips 
6. JTree and XML documents 
7. Custom editors and renderers 

17.5  Directories tree: part III - tooltips

As we discussed in chapter 5, tooltips are commonly used to display helpful information. In this example we will show how to use tooltips specific to each tree cell. The key point (which is mentioned in the JTree documentation, but can be easily overlooked) is to register the tree component with the ToolTipManager instance:

  ToolTipManager.sharedInstance().registerComponent(myTree);

Without doing this, no tooltips will appear over our tree (refer back to chapter 2, section 2.5, for more about shared instances and service classes).

The JTree component overrides the getToolTipText(MouseEvent ev) method inherited from JComponent, and delegates this call to the tree's cell renderer component. By implementing the getToolTipText(MouseEvent ev) method in our renderer we can allow cell-specific tooltips. Specifically, we can can return the tooltip text as a String depending on the last node passed to the getTreeCellRendererComponent() method. Alternatively we can subclass our JTree component and provide our own getToolTipText() implementation. We use the latter method here.

Figure 17.5 JTree with node-specific tooltips.

<<file figure17-5.gif>>

The Code: FileTree2.java

see \Chapter17\4

import java.awt.*;

import java.awt.event.*;

import java.io.*;

import java.util.*;

import javax.swing.*;

import javax.swing.tree.*;

import javax.swing.event.*;

public class FileTree3 extends JFrame

{

  // Unchanged code from section 17.4

  public FileTree3() {

    super("Directories Tree [Tool Tips]");

    setSize(400, 300);

    getContentPane().setLayout(new BorderLayout());

    // Unchanged code

    m_model = new DefaultTreeModel(top);

    m_tree = new JTree(m_model)

    {

      public String getToolTipText(MouseEvent ev)

      {

        if(ev == null)

          return null;

        TreePath path = m_tree.getPathForLocation(ev.getX(),

          ev.getY());

        if (path != null)

        {

          FileNode fnode = getFileNode(getTreeNode(path));

          if (fnode==null)

            return null;

          File f = fnode.getFile();

          return (f==null ? null : f.getPath());

        }

        return null;

      }

    };

    ToolTipManager.sharedInstance().registerComponent(m_tree);

    // The rest of the code is unchanged

Understanding the Code

Class FileTree3

This example anonymously subclasses the JTree component to override getToolTipText(MouseEvent ev), which finds the path closest to the current mouse location, determines the FileNode at the end of that path, and returns the full file path to that node as a String for use as tooltip text. Also note that our JTree component is manually registered with the shared instance of ToolTipManager, as discussed above.

Running the Code

Figure 17.5 shows our directories tree application displaying a tooltip with text specifying the full path of the directory corresponding to the node nearest to the current mouse location.

UI Guideline : Tooltips as an aid to selection

Tooltips have two really useful advantages for tree cells. Trees have a habit of wandering off to the right hand side of a display, particularly in deep hierarchies. This may result in cell labels being clipped. Using the tooltip to display the full length cell label, will speed selection and prevent the need for scrolling.

The second use is shown clearly in this example. The tooltip is used to unravel the hierarchy. This would be particularly useful when the original root node is off screen. The User can see quickly, the full hierarchical path to the selected cell. This is a very powerful aid to correct selection. Another example of additional coding effort providing improved usability.



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