javax.swing
Interface Action

All Known Implementing Classes:

AbstractAction

public interface Action

extends ActionListener

The JFC Action interface provides a useful extension to the ActionListner interface in cases where the same functionality may be accessed by several controls.

In addition to the actionPerformed method defined by the ActionListener interface, this interface allows the application to define, in a single place:

• One or more text strings that describe the function. These strings can be used, for example, to display the flyover text for a button or to set the text in a menu item.
• One or more icons that depict the function. These icons can be used for the images in a menu control, or for composite-entries in a more sophisticated user-interface.
• The enabled/disabled state of the functionality. Instead of having to separately disable the menu-item and the toolbar-button, the application can disable the function that implements this interface. All components which are registered as listeners for the state-change then know to disable event-generation for that item and to modify the display accordingly.

Containers in the Swing set like menus and toolbars know how to add an Action object, as well as other components, using a version of the add method. When an Action object is added to such a container, the container:

1. Creates a component that is appropriate for that container (a toolbar creates a button component, for example).
2. Gets the appropriate property(s) from the Action object to customize the component (for example, the icon image and flyover text).
3. Checks the intial state of the Action object to determine if it is enabled or disabled, and renders the component in the appropriate fashion.
4. Registers a listener with the Action object so that is notified of state changes. When the Action object changes from enabled to disabled, or back, the container makes the appropriate revisions to the event-generation mechanisms and renders the component accordingly.

For example, both a menu item and a toolbar button could access a Cut action object. The text associated with the object is specified as "Cut", and an image depicting a pair of scissors is specified as its icon. The Cut action-object can then be added to a menu and to a toolbar. Each container does the appropriate things with the object, and invokes its actionPerformed method when the component associated with it is activated. The application can then disable or enable the application object without worrying about what user-interface components are connected to it.

This interface can be added to an existing class or used to create an adapter (typically, by subclassing AbstractAction). The Action object can then be added to multiple action-aware containers and connected to Action-capable components. The GUI controls can then be activated or deactivated all at once by invoking the Action object's setEnabled method. Note that Action implementations tend to be more expensive in terms of storage than a typical ActionListener, which does not offer the benefits of centralized control of functionality and broadcast of property changes. For this reason, you should take care to only use Actions where their benefits are desired, and use a simple ActionListener where they are not necessary.

See Also:

AbstractAction

Field Summary

static String	DEFAULT Useful constants that can be used as the storage-retreival key when setting or getting one of this object's properties (text or icon).
static String	LONG_DESCRIPTION The key used for storing a longer description for the action, could be used for context-sensitive help.
static String	NAME The key used for storing the name for the action, used for a menu or button.
static String	SHORT_DESCRIPTION The key used for storing a short description for the action, used for tooltip text.
static String	SMALL_ICON The key used for storing a small icon for the action, used for toolbar buttons.

Method Summary

void	addPropertyChangeListener(PropertyChangeListener listener) Add a PropertyChange listener.
Object	getValue(String key) Gets one of this object's properties using the associated key.
boolean	isEnabled() Sets the enabled state of the Action.
void	putValue(String key, Object value) Sets one of this object's properties using the associated key.
void	removePropertyChangeListener(PropertyChangeListener listener) Remove a PropertyChange listener.
void	setEnabled(boolean b) Tests the enabled state of the Action.

Methods inherited from interface java.awt.event.ActionListener

actionPerformed

Field Detail

DEFAULT

public static final String DEFAULT

Useful constants that can be used as the storage-retreival key when setting or getting one of this object's properties (text or icon).

NAME

public static final String NAME

The key used for storing the name for the action, used for a menu or button.

SHORT_DESCRIPTION

public static final String SHORT_DESCRIPTION

The key used for storing a short description for the action, used for tooltip text.

LONG_DESCRIPTION

public static final String LONG_DESCRIPTION

The key used for storing a longer description for the action, could be used for context-sensitive help.

SMALL_ICON

public static final String SMALL_ICON

The key used for storing a small icon for the action, used for toolbar buttons.

Method Detail

getValue

public Object getValue(String key)

Gets one of this object's properties using the associated key.

See Also:

putValue(java.lang.String, java.lang.Object)

putValue

public void putValue(String key,
                     Object value)

Sets one of this object's properties using the associated key. If the value has changed, a PropertyChangeEvent is sent to listeners.

Parameters:

key - a String containing the key

value - an Object value

setEnabled

public void setEnabled(boolean b)

Tests the enabled state of the Action. When enabled, any component associated with this object is active and able to fire this object's actionPerformed method. If the value has changed, a PropertyChangeEvent is sent to listeners.

Parameters:

b - true to enable this Action, false to disable it

isEnabled

public boolean isEnabled()

Sets the enabled state of the Action. When enabled, any component associated with this object is active and able to fire this object's actionPerformed method.

Returns:

true if this Action is enabled

addPropertyChangeListener

public void addPropertyChangeListener(PropertyChangeListener listener)

Add a PropertyChange listener. Containers and attached components use these methods to register interest in this Action object. When its enabled state or other property changes, the registered listeners are informed of the change.

Parameters:

listener - a PropertyChangeListener object ...

removePropertyChangeListener

public void removePropertyChangeListener(PropertyChangeListener listener)

Remove a PropertyChange listener.

Parameters:

listener - a PropertyChangeListener object ...

See Also:

addPropertyChangeListener(java.beans.PropertyChangeListener)