oracle.ide.panels
Interface Traversable

All Known Implementing Classes:

DefaultTraversablePanel

public interface Traversable

The methods defined in the Traversable interface specify the operations that a UI component must support in order to be traversed in complex UI widgets such as a property dialog, a wizard, or any other panel-based UI.

Property dialogs and wizards typically involve some set of panels that are displayed to the user. In the case of property dialogs, the user can traverse the panels in a random-access manner; in wizards, the user traverses the panels in a sequential order. Often, the data structures being edited by the panels do not necessarily correspond to the structure of the panels. That is, a single panel may edit multiple data objects, or multiple panels may edit a single data object. Moreover, values displayed in one panel may also be affected by edits performed in another panel.

The Traversable interface specifies the protocol through which panels can communicate indirectly with each other. The onEntry(TraversableContext) and onExit(TraversableContext) methods comprise the main part of the interaction. The getExitTransition() method is used when the Traversable appears in an FSMWizard; a Traversable that is not used in FSMWizard should just return null from getExitTransition().

The Traversable implementation finds the data objects that it needs by querying the TraversableContext. The TraversableContext uses a Namespace to hold data objects. Therefore the Traversable must be able to find its data objects using predefined names. Consequently, the names and data types of the required data objects must be documented by every Traversable implementation. It is then the responsibility of the UI container and the class instantiating the UI container to ensure that the Namespace is populated with the appropriate data objects before entering the Traversable.

The Traversable interface is designed to allow a single panel to be used in both a property dialog and a wizard. Generally, a property dialog is used to edit the properties of an existing object, and a wizard is used to guide the user through the creation of a new object. In some cases, the property dialog and the wizard are nearly identical and may even use the same panels; in other cases, the wizard only displays the most commonly edited properties and leaves the more advanced editing to be performed in the property dialog. Panels that implement the Traversable interface are available to be reused in either a property dialog or a wizard, provided that the data objects are properly loaded into the Namespace used by the TraversableContext.

See Also:

MetaTraversable, Navigable, MDDPanel, Step, FSMWizard

Method Summary

java.awt.Component	getComponent() Normally, the Traversable class will itself be the UI Component.
java.lang.Object	getExitTransition() Returns the exit transition that can be used by a Traversable-aware wizard.
java.lang.String	getHelpID() Returns the context-sensitive help topic ID to use for this Traversable.
void	onEntry(TraversableContext dataContext) This method is called when the Traversable is being entered.
void	onExit(TraversableContext dataContext) This method is called when the Traversable is being exited.

Method Detail

onEntry

public void onEntry(TraversableContext dataContext)

This method is called when the Traversable is being entered. The data that the Traversable should use to populate its UI components comes from the specified TraversableContext.

When the same Traversable is entered more than once in the course of interacting with the user, the Traversable needs to reload the data directly from the TraversableContext rather than caching data objects. Some reasons for this include:

• Other Traversables may edit the data objects or even replace them.
• The same Traversable instance may be used for editing multiple different instances of the same object type.

Loading data directly from the TraversableContext is the best way to ensure that the Traversable will not be editing the wrong data.

The Traversable should not even cache references to data objects between invocations of onEntry and onExit(TraversableContext) because the UI container is not required to guarantee that the references will be identical.

Parameters:

dataContext - The data wrapper where the Traversable locates the data that it needs to populate the UI.

getComponent

public java.awt.Component getComponent()

Normally, the Traversable class will itself be the UI Component. Therefore, getComponent() typically just returns this. In this situation the getComponent() method then is simply a means of avoiding a type cast.

In other cases, it would be useful to have the ability to return a different Component based on the contents of the TraversableContext that is passed to the onEntry(TraversableContext) method. UI containers (e.g. property dialogs and wizards) that are designed to use the Traversable interface must call the onEntry(TraversableContext) method before calling getComponent(). This allows a Traversable implementation to have the opportunity to configure the UI Component or even create a new one before it is displayed.

In either situation, the implementation should strive to return the same Component instance as often as possible rather than creating a new instance becaues the UI container will call this method frequently.

Returns:

The UI Component that the user interacts with for creating or editing an object.

onExit

public void onExit(TraversableContext dataContext)
            throws TraversalException

This method is called when the Traversable is being exited. At this point, the Traversable should copy the data from its associated UI back into the data structures in the TraversableContext.

If the Traversable should not be exited because the user has entered either incomplete, invalid, or inconsistent data, then this method can throw a TraversalException to indicate to the property dialog or wizard that validation failed and that the user should not be allowed to exit the current Traversable. Refer to the TraversalException javadoc for details on passing the error message that should be shown to the user.

Parameters:

dataContext - The data object where changes made in the UI should be copied so that the changes can be accessed by other Traversables.

Throws:

TraversalException - if the user has entered either incomplete, invalid, or inconsistent data. This exception prevents the property dialog or wizard from continuing and forces the user to stay on the current Traversable until the data entered is valid or the user cancels. The exception class itself is capable of carrying an error message that will be shown to the user. Refer to its javadoc for details.

getExitTransition

public java.lang.Object getExitTransition()

Returns the exit transition that can be used by a Traversable-aware wizard. The wizard can use the exit transition to direct the user through an alternate or streamlined set of panels based on their current input.

If the Traversable implementation does not support multiple exit transitions or is not used in a wizard, then this method should just return null.

Returns:

The exit transition for the Traversable that is used by dynamic interview-style wizards to determine the next course of action. A Traversable class that does not support multiple possible transitions should just return null.

getHelpID

public java.lang.String getHelpID()

Returns the context-sensitive help topic ID to use for this Traversable. A null return value means that the Traversable implementation doesn't specify a help topic ID. However, there are other ways that a help topic ID could get associated with a Traversable.

Specifically, when a Traversable instance is created by a MetaTraversable such as Step or Navigable in the context of a Navigable container such as MDDPanel, TabbedPanel or FSMWizard, the help ID is searched according to the following order:

1. MetaTraversable#getHelpID()
2. getHelpID(). This may lead into a recursion if the Traversable's Component is a nested Navigable container.
3. oracle.bali.ewt.help.HelpUtils.getHelpID( getComponent() )
4. oracle.bali.ewt.help.HelpUtils.getHelpID(...) on the Navigable container itself.
5. null

The search returns the first non-null help ID encountered or else null if all possible sources of a help ID returned null.

Since a Navigable wraps a Traversable, and a Traversable wraps a Component, the priority order for determining the help ID is based on giving the outer-most wrapper the opportunity to override. The Navigable container has the lowest priority because containers such as MDDPanel, TabbedPanel, and FSMWizard don't normally have a help topic ID of their own, since help topics tend to be on a per page basis.

For most cases the recommended approach is to have the Traversable specify the help ID. However, when the same Traversable can be used in different contexts, then specifying or overriding the help ID from the MetaTraversable could be better, especially if that avoids the need for conditional logic in Traversable.getHelpID(). If no dynamic behavior is needed in determining the help ID, then the implementation can probably just subclass DefaultTraversablePanel and call the DefaultTraversablePanel.setHelpID(String) method from the subclass constructor.

The getHelpID() method is called only when the user requests help, so the actual help ID may be determined dynamically (e.g. return a different ID depending on the state of the UI).