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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!

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Page: 5/6 



Previous Page Previous Page (4/6) - Next Page (6/6) Next Page
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

25.5  Customizing the JHelp viewer

So far we've seen how to add the help viewer to an application and invoke it through pressing F1 or a button. However, we may very well want to customize help functionality by adding a component to the help viewer toolbar, or adding a custom navigational view. The current release of the JavaHelp does include a fairly powerful GUI, however, there are certainly cases where this is not enough. In this and the next section we will show how to integrate two new features into the help viewer: a "Home" toolbar button switching to the home help topic (specified by the <homeID> HelpSet file tag), and a "History" view providing quick return to a specific previously viewed topic.

The bad news is that (at least in this release) JavaHelp does not provide any direct access to the JHelp instance constituting the help viewer. So no customization can be done though provided functionality. The good news is that by taking advantage of the fact that JHelp is a java.awt.Container subclass, we can gain access to its child components indirectly and do what we need.

Reference: We did a similar thing with JFileChooser in chapter 14 to gain access to its embedded JList. This was necessary to allow multiple selection, which is not implemented correctly as of Java 2 FCS.

The following example builds off of the previous FTP client example, and shows how to customize the help viewer by adding a "Home" button to its toolbar.

Note: This solution is highly dependant on the construction of JHelp, which may very well change in future implemenatations. However, it illustrates some general techniques that can be used when components are not build as flexible as they should be.

Note: This example, and the example in section 25.6, requires Java2 because new functionality built into java.awt.Frame and java.io.File is used here (explained below).

Figure 25.4 JHelp viewer with a custom toolbar button for jumping to the home topic specified in a HelpSet file.

<<file figure25-4.gif>>

The Code: FTPApp.java

see \Chapter25\3

// Unchanged imports from section 25.4

public class FTPApp extends JFrame

{

  // Unchanged code from section 25.4

  public FTPApp() {

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

    // Unchanged code from section 25.4

    WindowListener wndCloser = new WindowAdapter() {

      public void windowClosing(WindowEvent e) {

        disconnect();

        System.exit(0);

      }

      Frame m_helpFrame = null;

      public void windowDeactivated(WindowEvent e) {

        if (m_helpFrame != null)

          return;

        Frame[] frames = getFrames(); // Only available in Java 2

        for (int k = 0; k < frames.length; k++) {

          if (!(frames[k] instanceof JFrame))

            continue;

          JFrame jf = (JFrame)frames[k];

          if (jf.getContentPane().getComponentCount()==0)

            continue;

          Component c = jf.getContentPane().

            getComponent(0);

          if (c == null || !(c instanceof JHelp))

            continue;

          m_helpFrame = jf;

          JHelp jh = (JHelp)c;

          for (int s=0; s<jh.getComponentCount(); s++) {

            c = jh.getComponent(s);

            if (c == null || !(c instanceof JToolBar))

              continue;

            JToolBar jtb = (JToolBar)c;

            jtb.addSeparator();

            JButton home = new JButton(new

              ImageIcon("Home.gif"));

            home.setToolTipText("Home Topic");

            jtb.add(home);

            ActionListener alst = new ActionListener() {

              public void actionPerformed(ActionEvent e) {

                try {

                  m_hb.setCurrentID(m_hs.getHomeID());

                }

                catch (Exception ex) {}

              }

            };

            home.addActionListener(alst);

          }

        }

      }

    };

    addWindowListener(wndCloser);

    // Unchanged code from section 25.4

  }

// Unchanged code from section 25.4

Understanding the Code

Class FTPApp

The idea behind this example is that when the application's frame is deactivated, this may have occurred because the help viewer's frame has become activated. So at that moment we can check all existing frames in the current JVM, and check whether they hold an instance of JHelp as a first child in the content pane. If so, we gain access to the JHelp instance and add our custom component to it.

To accomplish this, significant modification has been made to our WindowListener implementation, which previously only implemented the windowClosing() method. The Frame m_helpFrame instance variable holds a reference to the help viewer's frame (note that this frame is created only once and is hidden/shown as needed after that). The windowDeactivated() method checks this variable, and if it hasn't been determined yet (i.e. if it is null) it retrieves an array of all the frames created by this JVM using the static Frame.getFrames() method (another nice new feature in Java 2). All these frames are examined in turn. If one of them is an instance of JFrame and has an instance of JHelp as its first child, we take a reference to that child, cast it to JHelp, and, in turn, examine all its children. We know that one of these children should be an instance of JToolBar (since this only occurs before JHelp first becomes visible, there is no possibility that the toolbar has been undocked and left floating). As soon as it is found, we add() a JButton which calls setCurrentID() on our HelpSet when pressed:

    m_hb.setCurrentID(m_hs.getHomeID());

The Map.ID instance returned by the getHomeID() method is supplied as an argument to this call, which sets the current topic in the viewer to the home topic specifed in our HelpSet file.

Running the Code

Figure 25.4 shows the JHelp viewer with a new toolbar button. Pressing this button shows the home topic as specified by the <homeID> tag in our HelpSet file. We can use a similar technique to add any other component to this toolbar, or to another JHelp constituent.



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