Actionpublic interface Action implements ActionListenerThe Action interface provides a useful extension to the
ActionListener
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.
Certain containers, including menus and tool bars, know how to add an
Action object. When an Action object is added
to such a container, the container:
- Creates a component that is appropriate for that container
(a tool bar creates a button component, for example).
- Gets the appropriate property(s) from the
Action object to
customize the component (for example, the icon image and flyover text).
- Checks the initial state of the
Action object to determine
if it is enabled or disabled, and renders the component in the
appropriate fashion.
- 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 tool bar. 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 simple ActionListeners elsewhere. |
| Fields Summary |
|---|
| public static final String | DEFAULTNot currently used. | | public static final String | NAMEThe key used for storing the String name
for the action, used for a menu or button. | | public static final String | SHORT_DESCRIPTIONThe key used for storing a short String
description for the action, used for tooltip text. | | public static final String | LONG_DESCRIPTIONThe key used for storing a longer String
description for the action, could be used for context-sensitive help. | | public static final String | SMALL_ICONThe key used for storing a small Icon, such
as ImageIcon, for the action, used for toolbar buttons. | | public static final String | ACTION_COMMAND_KEYThe key used to determine the command String for the
ActionEvent that will be created when an
Action is going to be notified as the result of
residing in a Keymap associated with a
JComponent. | | public static final String | ACCELERATOR_KEYThe key used for storing a KeyStroke to be used as the
accelerator for the action. | | public static final String | MNEMONIC_KEYThe key used for storing a KeyEvent to be used as
the mnemonic for the action. |
| Methods Summary |
|---|
| public void | addPropertyChangeListener(java.beans.PropertyChangeListener listener)Adds 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.
| | public java.lang.Object | getValue(java.lang.String key)Gets one of this object's properties
using the associated key.
| | public boolean | isEnabled()Returns 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.
| | public void | putValue(java.lang.String key, java.lang.Object value)Sets one of this object's properties
using the associated key. If the value has
changed, a PropertyChangeEvent is sent
to listeners.
| | public void | removePropertyChangeListener(java.beans.PropertyChangeListener listener)Removes a PropertyChange listener.
| | public void | setEnabled(boolean b)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.
If the value has changed, a PropertyChangeEvent is sent
to listeners.
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