## Implementing Context-Sensitive Help

The JavaHelp system provides classes and methods that help you implement context-sensitive help in your applications. The following sections:

- Summarize the context-sensitive help system
- Describe the basic elements of the system
- Describe how to implement context-sensitive help
- Describe the APIs that support dynamic ID assignment

### Summary

The following table summarizes the context-sensitive help system.

CSH Type | Activation Mechanism | Object for Which Help Is Provided | Implementation Steps
--- | --- | --- | ---

Window-Level

Press F1 (or Help) key.

Window with focus

- Set helpIDs for components
- Capture F1 key press
- Get window that has focus
- Get helpID for window
- Display help (optionally in a specific presentation)

Field-Level

1. Activate field-level help.
2. Navigate with mouse or keyboard.
3. Select object.

Selected object

- Set helpIDs for components
- Activate field-level help (button or menu item)
- Track context-sensitive events
- Get helpID for selected object
- Display help (optionally in a specific presentation)

Help Button
Menu Item

Click button or choose menu item.

Topic associated with button or menu item

- Create button or menu object
- Set helpID on object
- Get helpID on object
- Display help

System Initiated

Internal, varies.

Internal, varies

- Display help (optionally in a specific presentation)

### Basic Elements

This section describes the low-level elements used in implementing context-sensitive help.

| If you use the "convenience" methods in the `HelpBroker` object to implement context-sensitive help, these low-level elements are managed for you.

The basic steps for implementing context-sensitive help are:

1. Set and get `Component` help properties for GUI objects
2. Track context-sensitive events

#### Setting and Getting Component Help Properties

To provide context-sensitive help for GUI Components and menu items, you must associate a help ID with that `Component` or menu item. To make that association, you set the `helpID` property and (if you use multiple helpsets) the `HelpSet` for the `Component` or `MenuItem` The JavaHelp system `CSH` class provides the following convenient methods for setting and getting the `helpID` for `Component`s and `MenuItem`s:

#### setHelpIDString Component

     public static void setHelpIDString(Component comp, String helpID);

Sets the `helpID` for a component.

#### getHelpIDString Component

     public static String getHelpIDString(Component comp);

Returns the `helpID` for a component.

#### setHelpSet Component

     public static void setHelpSet(Component comp, HelpSet hs);

Sets the `HelpSet` for a component.

#### getHelpSet Component

     public static HelpSet getHelpSet(Component comp);

Returns the `HelpSet` of a component.

#### setHelpIDString MenuItem

     public static void setHelpIDString(MenuItem comp,
                                        String helpID);

Sets the `helpID` for a menu item.

#### getHelpIDString MenuItem

     public static String getHelpIDString(MenuItem comp);

Returns the `helpID` for a menu item.

#### setHelpSet MenuItem

     public static void setHelpSet(MenuItem comp, HelpSet hs);

Sets the helpset for a menu item.

#### getHelpSet MenuItem

     public static HelpSet getHelpSet(MenuItem comp);

Returns the helpset of a menu item.

#### Tracking Context-Sensitive Events

The context-sensitive help class provides the `CSH.trackCSEvents` method, which you can use to easily track context-sensitive events. This method traps all non-navigational events until an object is selected. It returns the selected object. Following is the declaration for the method:

     public static Component CSH.trackCSEvents()

### Implementing Context-Sensitive Help

The sections that follow describe how to use the JavaHelp system to implement various forms of context-sensitive help.

#### The `HelpBroker`

The JavaHelp system defines a `HelpBroker` interface that provides convenience methods that greatly simplify the job of implementing context-sensitive help. `HelpBroker` methods hide much of the underlying implementation details. In exchange, using the `HelpBroker` limits the flexibility of your implementation. For example, if you use the `DefaultHelpBroker`, you must display help information in the standard help viewer.

| You can implement context-sensitive help without using the `HelpBroker`, or you can use the `HelpBroker` for some tasks and not for others. For example, if your implementation requires something not provided in the `HelpBroker`, such as displaying context-sensitive help in a different viewer, you must use the basic classes (`CSH`, `JHelp`) directly. For information about those classes, use the JavaHelp system `apiviewer` command.

| With some of these methods, you can specify the presentation type, the type of window in which the help topics is displayed. The examples show generic names for popup windows and secondary windows that will always work. However, it is possible that specific presentation definitions have been provided in the helpset file by the help author. Since the help author can define attributes of presentations, including their size, their position, and the number and type of panes, if presentations are defined in the helpset file, you might want to use their names in help calls.

A `HelpBroker`'s convenience methods enable:

- Window-level help for a dialog box
- Help buttons for dialog boxes
- Buttons and menu items that activate field-level help

The following illustration shows how the HelpBroker and its context-sensitive methods (`hb.*`) are used with other JavaHelp system components:

#### `HelpBroker` Context-Sensitive Methods

A `HelpBroker` provides the following context-sensitive methods:

#### setHelpSet

     public void setHelpSet(HelpSet hs);

Sets the `HelpSet` for the current `HelpBroker` (there can be only one `HelpSet` per `HelpBroker`). If you use this method to change helpsets, the displays in the corresponding `JHelp` component and `JHelpNavigator` are changed.

#### getHelpSet

     public HelpSet getHelpSet();

Gets the current `HelpSet` for the `HelpBroker`.

#### setCurrentID

     public void setCurrentID(Map.ID id) throws BadIDException;

Sets the current ID that is to be displayed in the help viewer. If `hs` is null, the `HelpBroker`'s current `HelpSet` is used. If `hs` is different from the current `HelpSet` (and not contained in the current `HelpSet`), the `setHelpSet` method is executed.

#### setCurrentURL

     public void setCurrentURL(URL url, HelpSet hs) throws BadIDException;

Displays the specified URL in the help viewer. If `hs` is null, the `HelpBroker`'s current `HelpSet` is used. If `hs` is different from the current `HelpSet` (and not contained in the current `HelpSet`), the `setHelpSet` method is executed.

#### enableHelpKey

    public void enableHelpKey(Component comp, String id, HelpSet hs,
                              String presentationType, String presentationName);

Enables the Help key on a Component (the F1 key on Windows machines). This method works best when the component is the `rootPane` of a `JFrame` in Swing-based applications, or a `java.awt.Window` (or subclass thereof) in AWT-based applications. This method sets the default `helpID` and `HelpSet` for the `Component` and registers keyboard actions to trap the "Help" keypress. If the object with the current focus has a `helpID`, the `helpID` is displayed when the Help key is pressed; otherwise, the default `helpID` is displayed. You can optionally specify the type of help window in which a help topic is displayed.

For example, the following code specifies that the help presentation is a secondary window named `mainSW`:

     JTextArea newText = new JTextArea();

     hb.enableHelp(newText, "debug.overview", hs);
     . . .
     rootpane = frame.getRootPane();
     mainHelpBroker.enableHelpKey(rootpane,
                                  "top",
                                  null,
                                  "javax.help.SecondaryWindow",
                                  "mainSW");

#### enableHelp Component

    public void enableHelp(Component comp, String id, HelpSet hs);

Enables help activation for a help component (for example, a Help button). This method:

- Registers the `helpID` and `HelpSet` on `comp`
- Sets the `HelpBroker`'s `HelpActionListener` on `comp`

#### enableHelp MenuItem

    public void enableHelp(MenuItem comp, String id, HelpSet hs)

Enables help activation for a `MenuItem`. This method:

- Registers the `helpID` and `HelpSet` on `comp`
- Sets the `HelpBroker`'s `HelpActionListener` on `comp`

#### enableHelpOnButton Component

      public void enableHelpOnButton(
                     Component comp, String id, HelpSet hs,
                     String presentationType,
                     String presentationName);

Enables help for a `Component`. This method sets the `helpID` and `HelpSet` for the `Component` and adds an `actionListener`. When an action is performed it displays the `Component`'s `helpID` and `HelpSet` in the default viewer. If the `Component` is not a `javax.swing.AbstractButton` or a `java.awt.Button`, an `IllegalArgumentException` is thrown. You can optionally specify the type of help window in which a help topic is displayed.

For example, the following code specifies that the help presentation is a secondary window named `mainSW`:

     JButton helpButton = new JButton("Help",
                                      "javax.help.SecondaryWindow",
                                      "mainSW");

     mainHelpBroker.enableHelpOnButton(helpButton,
                                       "browse.strings",
                                       null,
                                       "javax.help.SecondaryWindow",
                                       "mainSW");

#### enableHelpOnButton MenuItem

     public void enableHelpOnButton(MenuItem comp, String id, HelpSet hs,
                                    String presentationType,
                                    String presentationName);

Enables help for a `MenuItem`. This method sets the `helpID` and `HelpSet` for the `Component` and adds an `actionListener`. When an action is performed it displays the `helpID` and `HelpSet` in the default viewer. You can optionally specify the type of help window in which a help topic is displayed.

#### `CSH` Inner Classes

The `CSH` class contains three inner classes that provide support for context-sensitive help.

#### `CSH.DisplayHelpAfterTracking`

     CSH.DisplayHelpAfterTracking(HelpSet hs,
                                 String presentationType,
                                 String presentationName)

This class defines an `ActionListener` that displays help for a selected object after tracking context-sensitive events. Its constructor takes a `HelpBroker` object. You can optionally specify the type of help window in which the help topic is displayed. For example, you could display help for a toolbar button in a popup window as follows:

     JToolBar toolbar=new JToolBar();
     . . .
     helpbutton= addButton(toolbar, "images/help.gif", "help");
     helpbutton.addActionListener(
       new CSH.DisplayHelpAfterTracking (mainHS,
                                         "javax.help.Popup",
                                         null));

#### `CSH.DisplayHelpFromFocus`

     CSH.DisplayHelpFromFocus(HelpSet hs,
                              String presentationType,
                              String presentationName)

An `ActionListener` that displays the help of the object that currently has focus. This method is used to enable a `HelpKey` action listening for components other than the `RootPane` or window. This listener determines if the object with the current focus has a `helpID`, and if it does the helpID is displayed. If the object does not have a `helpID`, the `helpID` on the action's source is displayed (if one exists). You can optionally specify the type of help window in which the help topic is displayed.

#### `CSH.DisplayHelpFromSource`

     CSH.DisplayHelpFromSource(HelpSet hs,
                               String presentationType,
                               String presentationName)

An actionListener that gets the `helpID` for the action source and displays the helpID in the help viewer. Its constructor takes a HelpBroker object. You can optionally specify the type of help window in which the help topic is displayed.

#### Window-Level Help

Start your window-level help implementation by setting the helpID and (if you use multiple helpsets) the `HelpSet` for each component for which you want help. If you do not set help for a given component, `CSH.getHelpID()` recursively searches through the component's ancestors until it finds the first ancestor with a helpID, or until it reaches the last ancestor. For example:

                           :
    	JTextArea newText = new JTextArea();
    	hb.enableHelp(newText, "debug.overview", hs);
    	                   :

After you set the helpID and helpset for all components, use the HelpBroker `enableHelpKey()` method to enable the F1 key for the frame's RootPane. The `hb.getHelpKeyActionListener()` method enables the F1 key on `ActionListener` objects other than root panes. For example, the following code displays the help in the default viewer:

                       :
        rootpane = frame.getRootPane();
        mainHelpBroker.enableHelpKey(rootpane, "top", null);
                       :

If you want to display help in a popup window, substitute the following line of code:

        mainHelpBroker.enableHelpKey(rootpane, "top", null,
                                     "javax.help.Popup", null);

If you want to display help in a secondary window named `mainSW`, substitute the following line of code:

        mainHelpBroker.enableHelpKey(rootpane, "top", null,
                                     "javax.help.SecondaryWindow",
                                     "mainSW");

#### Field-Level Help

Start your field-level help implementation by setting the helpID and (if you use multiple helpsets) helpset for each component for which you want help. If you do not set help for a given component, `CSH.getHelpID()` recursively searches through the component's ancestors until it finds the first ancestor with a helpID, or until it reaches the last ancestor.

After you set the helpID and helpset for all components, create a field-level help button or menu item. Set an ActionListener on the button or menu item with a HelpBroker object using `getOnItemActionActionListener`. For example:

    JToolBar toolbar=new JToolBar();
    CSH.setHelpID(toolbar,"toolbar.main");
                   :
    helpbutton= addButton(toolbar, "images/help.gif", "help");
    helpbutton.addActionListener(
            new CSH.DisplayHelpAfterTracking(mainHelpBroker));

The following invocation would display the field-level help in a popup window:

    JToolBar toolbar=new JToolBar();
    CSH.setHelpID(toolbar,"toolbar.main");
                   :
    helpbutton= addButton(toolbar, "images/help.gif", "help");
    helpbutton.addActionListener(
            new CSH.DisplayHelpAfterTracking(mainHelpBroker,
                                             "javax.help.Popup",
                                             null));

The following invocation would display the field-level help in a secondary window:

    JToolBar toolbar=new JToolBar();
    CSH.setHelpID(toolbar,"toolbar.main");
                   :
    helpbutton= addButton(toolbar, "images/help.gif", "help");
    helpbutton.addActionListener(
            new CSH.DisplayHelpAfterTracking(mainHelpBroker,
                                             "javax.help.SecondaryWindow",
                                             "mainSW"));

#### Help Menu and Help Button Help

To implement Help menu or Help button help:

1. Create a menu item or button.
2. Set the `helpID` and (if you use multiple helpsets) the helpset on the object.
3. Enable help on the object with the `HelpBroker`.

The `CSH` class provides the `CSH.DisplayHelpFromSource` class to enable help on objects with types other than `AbstractButton`, `Button`, or `MenuItem`. For example:

    JButton helpButton = new JButton("Help");
    mainHelpBroker.enableHelpOnButton(helpButton, "browse.strings", null);

| `HelpBroker.enableHelpOnButton` uses `CSH.DisplayHelpFromSource` and also sets the appropriate ID on the `Button` and the `ActionListener` on the `Button`. If this example used `CSH.DisplayHelpFromSource` instead, it would have to set the ID and ActionListener explicitly. Using `HelpBroker` in this example simplifies the code.

#### System Initiated Help

All the other help activations discussed in this section result from the user's clicking a button, pressing a key, or selecting an item in the navigator or content viewer. With system initiated help, the action is not initiated by the user, but rather by the application, which recognizes that the user is need of help and automatically calls the help system. For example, the user might have repeatedly tried an operation that failed every time or canceled a task midway through an operation.

Although system initiated help is rarely implemented with the help viewer, it is simple to do so. When help is presented internally within an application, pass a valid helpID to a HelpBroker object. For example:

    	                   :
    	try {
    	    mainHelpBroker.setCurrentID(helpID);
    	} catch (Exception ee) {
    	    System.err.println("trouble with visiting id; "+ee);
    	}
    	                   :

If you wanted the help to display in a popup window, you could use the following code instead:

    	                   :
    	try {
                 Popup popup = (Popup)Popup.getPresentation(mainHS,null);
                 popup.setInvoker (component);
                 popup.setCurrentID (helpID);
                 popup.setDisplayed(true);
    	} catch (Exception ee) {
    	    System.err.println("trouble with visiting id; "+ee);
    	}
    	                   :

If you wanted the help to display in a secondary window, you could use the following code:

    	                   :
            try {
               mainHelpBroker.showID(helpID,
                                     "javax.help.SecondaryWindow",
                                     "main");
            } catch (Exception ee) {
              System.err.println("trouble with visiting id; "+ee); }
            }
                           :

#### Sample Code

The following example shows the code required for the different types of context-sensitive help using a default helpset:

                              :
       try {
    	    ClassLoader cl = ApiDemo.class.getClassLoader();
    	    URL url = HelpSet.findHelpSet(cl, helpsetName);
    	    mainHS = new HelpSet(cl, url);
    	} catch (Exception ee) {
    	    System.out.println ("Help Set "+helpsetName+" not found");
    	    return;
    	} catch (ExceptionInInitializerError ex) {
    	    System.err.println("initialization error:");
    	    ex.getException().printStackTrace();
    	}
    	mainHB = mainHS.createHelpBroker();
                               :
    	// Enable window-level help on RootPane
    	rootpane = frame.getRootPane();
    	mainHB.enableHelpKey(rootpane, "top", null);
                               :
    	// Enable field-level help on various components
    	JToolBar toolbar=new JToolBar();
    	CSH.setHelpIDString(toolbar,"toolbar.main");
                               :
    	//Enable Menu/Button help on Help menu item
    	helpbutton= addButton(toolbar, "images/help.gif", "help");
    	mainHelpBroker.enableHelpButton(helpbutton, "browser.strings", null);

    	sourceIFrame = new JInternalFrame("Source", true, true, true, true);
    	CSH.setHelpIDString(sourceIFrame, "edit.editsource");

    	JTextArea newtext=new JTextArea();
    	CSH.setHelpIDString(newtext, "build.build");

    	newtext = new JTextArea();
    	CSH.setHelpIDString(newtext, "debug.overview");

    	newtext = new JTextArea();
    	CSH.setHelpIDString(newtext, "browse.strings");
                               :
    	// System Level help somewhere within the code
    	try {
    	    mainHelpBroker.setCurrentID(helpID);
    	} catch (Exception ee) {
    	    System.err.println("trouble with visiting id; "+ee);
    	}
                               :

### Dynamic Map ID Assignment

For certain objects, such as a `JTable`, having a single map ID per object is not sufficient. A technique is needed to determine programmatically the map ID based on cursor position, selection, or some other mechanism inherent to the object. For example a `Canvas` object might determine the map ID based on the object currently selected on the canvas or, alternatively, from the mouse cursor position.

The following APIs in the `CSH` class support dynamic ID assignment:

Name | Description
--- | ---
`addManager(CSH.Manager)` | Registers the specified manager to handle dynamic context-sensitive help.
`addManager(index,CSH.Manager)` | Registers the specified manager to handle dynamic context-sensitive help at the specified position in the list of managers.
`getManager(index)` | Returns the manager at the specified position in list of managers.
`getManagerCount()` | Returns the number of managers registered.
`getManagers()` | Returns array of managers registered.
`removeAllManagers()` | Remove all the dynamic context-sensitive help managers.
`removeManager(CSH.Manager)` | Remove the specified manager from the list of managers.
`removeManager(index)` | Remove the manager at the specified position in the list of managers.

Additionally the following interface has been defined in `CSH.Manager`:

Name | Description
--- | ---
`getHelpSet(Object, AWTEvent)` | Returns the `String` representing the `mapID` of the object based on the `AWTEvent`.
`getHelpIDString(Object, AWTEvent)` | Returns the `HelpSet` of the object based on the `AWTEvent`.

Instances of `CSH.Manager` work as filters. `CSH.getHelpIDString(comp)` and `CSH.getHelpSet(comp)` must call each registered `CSH.Manager`'s `getHelpIDString` or `getHelpSet` methods. If the `CSH.Manager` does not handle the component, it returns `null`. If no `CSH.Manager` provides a `HelpSet` or `HelpIDString` for the component, the `CSH` methods use the statically defined `HelpSet` and `HelpIDString` described in Using Statically Defined Help IDs. As with the statically defined `HelpSet` and `HelpIDString`, a failure in a request for a `HelpSet` and a `HelpIDString` is propagated to the component's parent.

#### Example: Dynamic Map ID Assignment

The following example shows how to use a component with a dynamically assigned `HelpSet` or a dynamically generated `HelpIDString`:

       class MyCSHManager implements CSH.Manager {
          HelpSet hs;
          JEditorPane editor;
          MyCSHManager(JEditorPane editor, HelpSet hs) {
             this.editor = editor;
             this.hs = hs;
          }
          public HelpSet getHelpSet(Object comp) {
             if (comp == editor) {
                return hs;
             }
             return null;
          }
          public String getHelpIDString(Object comp) {
             if (comp == editor) {
                return getHelpIDFromCaretPostion(editor);
             }
             return null;
          }
       }

You add the `CSH.Manager` to the `CSH` list of managers as follows:

`CSH.AddCSHManager(new MyCSHManager(editor, hs));`

### Using Statically Defined Help IDs

Context-sensitive help in the JavaHelp system is organized around the notion of the ID-URL map referred by the `<map>` section of a helpset file. The key concept is that of the `Map.ID`, which is comprised of a `String-HelpSet` instance pair. The `String` is intended to be unique in the local map of the helpset. This is very important when considering helpset merging; otherwise, IDs would be required to be unique over all helpsets that might ever be merged.

There are three tasks involved in assigning context-sensitive help to an application:

1. Defining the appropriate `String` ID-URL map
2. Assigning an ID to each desired visual object
3. Enabling a user action to activate the help

#### Defining the ID-URL Map

The `Map` interface provides a means for associating IDs (`HelpSet.string`) with URLs. One such map is constructed from one or more map files that provide a simpler `String` `ID` to URL mapping, with the `HelpSet` being given either explicitly or implicitly.

The JavaHelp system has two classes that implement the Map interface: `FlatMap` and `TryMap`. A `FlatMap` does not support nesting of other maps into it, while a `TryMap` does. A `FlatMap` is a simple implementation while `TryMap` should support inverse lookups (for example, `getIDFromURL`) more efficiently. The implementation of `TryMap` in version 1.0 of the JavaHelp system is not particularly efficient.

Both `FlatMap` and `TryMap` have public constructors. The constructor for `FlatMap` takes two arguments:

- A URL to a property file providing a list of `String` and URL pairs
- A `HelpSet`

The `HelpSet` is used together with each `String`-URL pair to create the actual `Map.ID` objects that comprise the `FlatMap`. The constructor for `TryMap` has no arguments. Its `Map` is created empty, and other `Map`s are added or removed from it.

The Map interface can also be implemented by some custom class. One such class could, for example, be used to programmatically generate the map.

#### Assigning an ID to Each Visual Object

The next step is to assign to each desired GUI object an ID that will lead to the desired help topic. There are two mechanisms that can be involved:

- An explicit ID, either a plain `String` or a `Map.ID`, is assigned to the GUI object.

  The two basic methods used to assign IDs are `setHelpIDString(Component, String)` and `setHelpSet(Component, String)`. If both are applied to a `Component`, then a `Map.ID` is assigned to that Component. If only `setHelpIDString()` is applied, then the `HelpSet` instance is obtained implicitly, as explained below in the next list item. A method overload is also provided for `MenuItem` objects.

  These methods take a `Component` as an argument. The implementation can vary depending on whether the argument is a `JComponent` or a plain AWT `Component`.

- A rule is used to infer the `Map.ID` for a GUI object based on the object's container hierarchy.

  The methods `getHelpIDString(Component)` and `getHelpSet(Component)` recursively traverse up the container hierarchy of the component trying to locate a `Component` that has been assigned a `String` ID. When found, the methods return the appropriate value. As before there is also an overloaded method for MenuItem.

#### Enabling a Help Action

The final step is to enable an action to trigger the presentation of the help data. `CSH` currently provides several `ActionListener` classes that can be used, described above under `CSH` Inner Classes. In addition, `HelpBroker` also provides some convenience methods that interact with these `ActionListener`s, as described above under HelpBroker Context-Sensitive Methods.

Since these methods are from a specific `HelpBroker`, if a `HelpSet` is not associated with the GUI object, the `HelpSet` of the `HelpBroker` is used automatically.

See also:

  Programming with the JavaHelp System
  Adding the JavaHelp System to Applications
  Embedding JavaHelp Components