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Swing Chapter 25. (Special topics) JavaHelp. Easy for reading, Click here!

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Swing Chapter 25. (Special topics) JavaHelp. Easy for reading, Click here!

[ Return to Swing (Book) ]

Page: 6/6 

Previous Page Previous Page (5/6)
Subpages: 1. JavaHelp introduction
2. JavaHelp API overview
3. Basic JavaHelp example
4. Adding dialog-style help
5. Customizing the JHelp viewer
5. Creating a custom help view

25.6  Creating a custom help view

As we mentioned earlier, JavaHelp allows developers to add a new navigator view by simply adding a new <view> tag to the HelpSet file. Unfortunately this navigator view cannot gain an access to the viewer component that displays it (it can only have access to a data file supplied as a parameter with the <data> tag, similar to TOC or index views). We can work around this limitation by using the same basic technique used in the previous section to access the JHelp toolbar. The following example adds a custom navigational view to the JHelp viewer tabbed pane to display a selectable, dynamically changeable help topic history.

Figure 25.5 Custom JavaHelp History view added to the JavaHelp viewer.

<<file figure25-5.gif>>

HelpSet file: FTP.hs

see \Chapter25\4\help\

   // Unchanged from section 25.4







The Code: FTPApp.java

see \Chapter25\4

// Unchanged imports from section 25.5

public class FTPApp extends JFrame


  // Unchanged code from section 25.5

  public FTPApp() {

    super("FTP Client [Help History]");

    // Unchanged code from section 25.5

    WindowListener wndCloser = new WindowAdapter() {

      // Unchanged code from section 25.5

      public void windowDeactivated(WindowEvent e) {

        // Unchanged code from section 25.5

          Enumeration en = jh.getHelpNavigators();

          while (en.hasMoreElements()) {

            JHelpNavigator jhn = (JHelpNavigator)


            NavigatorView view = jhn.getNavigatorView();

            if (view instanceof HistoryView)







    // Unchanged code from section 25.5


// Unchanged code from section 25.5

The Code: HistoryView.java

see \Chapter25\4

import java.awt.*;

import java.awt.event.*;

import java.util.*;

import java.net.*;

import javax.swing.*;

import javax.swing.event.*;

import javax.swing.tree.*;

import javax.help.*;

import javax.help.event.*;

public class HistoryView extends TOCView

 implements HelpModelListener


  protected DefaultMutableTreeNode m_topNode;

  protected JTree m_tree;

  protected DefaultTreeModel m_model;

  protected TreePath m_zeroPath;

  public HistoryView(HelpSet hs, String name, String label,

   Hashtable params) {

    super(hs, name, label, hs.getLocale(), params);


  public HistoryView(HelpSet hs, String name, String label,

   Locale locale, Hashtable params) {

    super(hs, name, label, locale, params);


  public Component createNavigator(HelpModel model) {

    JHelpNavigator navigator =

      new JHelpTOCNavigator(this, model);

    navigator.getUI().setIcon(new ImageIcon("History.gif"));

    return navigator;


  public static MutableTreeNode parse(URL url, HelpSet hs,

    Locale locale, TreeItemFactory factory) {

      return new DefaultMutableTreeNode("History");


  public void setNavigator(JHelpNavigator jhn) {


    try {

      Container c = jhn;

      while (!(c instanceof JTree))

        c = (Container)(c.getComponent(0));

      m_tree = (JTree)c;

      TOCItem top = new TOCItem();


      m_topNode = new DefaultMutableTreeNode(top);

      m_model = new DefaultTreeModel(m_topNode);


      m_zeroPath = new TreePath(new Object[] { m_topNode });


    catch (Exception ex) {





  public void idChanged(HelpModelEvent e) {

    // To avoid conflict with java.util.Map

    javax.help.Map.ID id = e.getID();

    if (m_topNode != null) {

      TOCItem item = new TOCItem(id, null, null);


      for (int k=0; k<m_topNode.getChildCount(); k++) {

        DefaultMutableTreeNode child =


        TOCItem childItem = (TOCItem)child.getUserObject();

        if (childItem.getID().equals(id))



      DefaultMutableTreeNode node =

        new DefaultMutableTreeNode(item);

      m_topNode.insert(node, 0);






Understanding the Code


One more <view> tag is now added to our FTP.hs XML HelpSet file to request the creation of a HistoryView with a name and label of "History." This results in a new navigator in JHelp's navigational view tabbed pane. This navigator is connected to an instance of our custom HistoryView class.

Class FTPApp

To connect the history view to the viewer itself, some code has been added to our windowDeactivated() method in the WindowAdapter inner class. This code retrieves all help views using the getHelpNavigators() method, examines all of them in turn, and, if an instance of our custom HistoryView class is found, calls the setNavigator() method to pass a reference to JHelpNavigator to it.

Note: The fact that we have to add this code to our application in order to use a custom view should immediately stand out as bad design, even though it is only called once (see previous example). We are forced to do this because the parent class, NavigatorView, does not provide any means of retrieving the associated instance of JHelpNavigator used to display it. This severely limits the abilities of help customization and contradicts the flexible, JavaBeans design of Swing components. We hope to see this limitation accounted for in future JavaHelp releases, making this workaround unnecessary.

Class HistoryView

This class represents a custom implementation of NavigatorView to provide easy access to previously viewed help topics. HistoryView implements HelpModelListener and extends TOCView to inherit its functionality and avoid writing our own NavigatorView sub-class. Instance variables:

JTree m_tree: the tree component used to display historical help topics.

DefaultMutableTreeNode m_topNode: the root node in the tree parenting all historical help topics. This node is not visible because the rootVisible property is set to false by the parent TOCView class.

DefaultTreeModel m_model: the historical tree model.

TreePath m_zeroPath: path to the root node.

The two available constructors delegate their work the corresponding superclass constructors. The createNavigator() method creates an instance of JHelpTOCNavigator (a sub-class of JHelpNavigator) to represent our historical view graphically, and assigns it a custom icon (to be displayed in JHelp's navigational views tabbed pane).

Since we are not intending to parse any external data files in our historical view (all data is generated by the help viewer itself at run-time), the parse() method simply creates and returns an instance of DefaultMutableTreeNode with user object "History," and no child nodes.

Our custom setNavigator() method establishes a connection between this view and the JHelpNavigator component supplied as parameter representing our history information graphically. First, this view is added as a HelpModelListener to the JHelpNavigator's HelpModel to receive HelpModelEvents when a change in the current help topic occurs. Second, we search for the JHelpNavigator's tree component by iterating through its containment hierarchy. Then the m_topNode variable is assigned a DefaultMutableTreeNode instance with a default TOCItem user object assigned a name of "History." We also assign the m_model variable as a reference to this tree's model, and m_zeroPath is used to store the path from the tree's root to m_topNode (which simply consists of m_topNode itself). Both variables are needed in idChanged().

The idChanged() method will be called when the current help topic is changed. This method receives an instance of HelpModelEvent which encapsultes, among other things, the new help topic ID. It then creates a new TOCItem using that ID, and checks all child nodes of m_topNode to find out whether the corresponding topic already exists in the history view. If so, it is removed to avoid redundancy. Then the new topic is inserted at the top of the tree. Thus the previously viewed topics appear listed from most recent at the top, to least recent at the bottom. Finally we call reload() on the tree model and expandPath() on the tree, using m_zeroPath, to make sure that the tree updates its graphical representation correctly after it is reloaded.

Note: Since the root tree node is hidden and the path to it is collapsed by default, no nodes in the view will be visible after a reload() unless we expand m_zeroPath programmatically.

That's all we need to do to create a history view. As soon as the user clicks on the topic listed in the help view, it will be displayed in the viewer because we inherit this functionality from TOCView.

Running the Code

Figure 25.5 shows the customized help viewer for our FTP Client example with the custom history view. Select several help topics in a row using the TOC or index views and then select the history view. Note that all visited help topics are listed in the reverse order that they were visited in. Click on any of these topics and note that viewer jumps to that topic (at the same time the selected topic is displayed it moves to the top of the history view, as expected).

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