public interface Action extends ActionListener
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:
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.
Action
Many of Swing's components have an Action property. When
an Action is set on a component, the following things
happen:
Action is added as an ActionListener to
the component.
Action.
PropertyChangeListener on the
Action so that the component can change its properties
to reflect changes in the Action's properties.
The following table describes the properties used by
Swing components that support Actions.
In the table, button refers to any
AbstractButton subclass, which includes not only
JButton but also classes such as
JMenuItem. Unless otherwise stated, a
null property value in an Action (or a
Action that is null) results in the
button's corresponding property being set to null.
| Component Property | Components | Action Key | Notes |
|---|---|---|---|
enabled
| All | The isEnabled method
| |
toolTipText
| All | SHORT_DESCRIPTION
| |
actionCommand
| All | ACTION_COMMAND_KEY
| |
mnemonic
| All buttons | MNEMONIC_KEY
| A null value or Action results in the
button's mnemonic property being set to
'\0'.
|
text
| All buttons | NAME
| If you do not want the text of the button to mirror that
of the Action, set the property
hideActionText to true. If
hideActionText is true, setting the
Action changes the text of the button to
null and any changes to NAME
are ignored. hideActionText is useful for
tool bar buttons that typically only show an Icon.
JToolBar.add(Action) sets the property to
true if the Action has a
non-null value for LARGE_ICON_KEY or
SMALL_ICON.
|
displayedMnemonicIndex
| All buttons | DISPLAYED_MNEMONIC_INDEX_KEY
| If the value of DISPLAYED_MNEMONIC_INDEX_KEY is
beyond the bounds of the text, it is ignored. When
setAction is called, if the value from the
Action is null, the displayed
mnemonic index is not updated. In any subsequent changes to
DISPLAYED_MNEMONIC_INDEX_KEY, null
is treated as -1.
|
icon
| All buttons except of JCheckBox,
JToggleButton and JRadioButton.
| either LARGE_ICON_KEY or
SMALL_ICON
| The JMenuItem subclasses only use
SMALL_ICON. All other buttons will use
LARGE_ICON_KEY; if the value is null they
use SMALL_ICON.
|
accelerator
| All JMenuItem subclasses, with the exception of
JMenu.
| ACCELERATOR_KEY
| |
selected
| JToggleButton, JCheckBox,
JRadioButton, JCheckBoxMenuItem and
JRadioButtonMenuItem
| SELECTED_KEY
| Components that honor this property only use
the value if it is non-null. For example, if
you set an Action that has a null
value for SELECTED_KEY on a JToggleButton, the
JToggleButton will not update it's selected state in
any way. Similarly, any time the JToggleButton's
selected state changes it will only set the value back on
the Action if the Action has a non-null
value for SELECTED_KEY.
Components that honor this property keep their selected state in sync with this property. When the same Action is used
with multiple components, all the components keep their selected
state in sync with this property. Mutually exclusive
buttons, such as JToggleButtons in a ButtonGroup,
force only one of the buttons to be selected. As such, do not
use the same Action that defines a value for the
SELECTED_KEY property with multiple mutually
exclusive buttons.
|
JPopupMenu, JToolBar and JMenu
all provide convenience methods for creating a component and setting the
Action on the corresponding component. Refer to each of
these classes for more information.
Action uses PropertyChangeListener to
inform listeners the Action has changed. The beans
specification indicates that a null property name can
be used to indicate multiple values have changed. By default Swing
components that take an Action do not handle such a
change. To indicate that Swing should treat null
according to the beans specification set the system property
swing.actions.reconfigureOnNull to the String
value true.
AbstractAction| Modifier and Type | Field and Description |
|---|---|
static String |
ACCELERATOR_KEY
The key used for storing a
KeyStroke to be used as the
accelerator for the action. |
static String |
ACTION_COMMAND_KEY
The 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. |
static String |
DEFAULT
Not currently used.
|
static String |
DISPLAYED_MNEMONIC_INDEX_KEY
The key used for storing an
Integer that corresponds
to the index in the text (identified by the NAME
property) that the decoration for a mnemonic should be rendered at. |
static String |
LARGE_ICON_KEY
The key used for storing an
Icon. |
static String |
LONG_DESCRIPTION
The key used for storing a longer
String
description for the action, could be used for context-sensitive help. |
static String |
MNEMONIC_KEY
The key used for storing an
Integer that corresponds to
one of the KeyEvent key codes. |
static String |
NAME
The key used for storing the
String name
for the action, used for a menu or button. |
static String |
SELECTED_KEY
The key used for storing a
Boolean that corresponds
to the selected state. |
static String |
SHORT_DESCRIPTION
The key used for storing a short
String
description for the action, used for tooltip text. |
static String |
SMALL_ICON
The key used for storing a small
Icon, such
as ImageIcon. |
| Modifier and Type | Method and Description |
|---|---|
void |
addPropertyChangeListener(PropertyChangeListener listener)
Adds a
PropertyChange listener. |
Object |
getValue(String key)
Gets one of this object's properties
using the associated key.
|
boolean |
isEnabled()
Returns 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)
Removes a
PropertyChange listener. |
void |
setEnabled(boolean b)
Sets the enabled state of the
Action. |
actionPerformedstatic final String DEFAULT
static final String NAME
String name
for the action, used for a menu or button.static final String SHORT_DESCRIPTION
String
description for the action, used for tooltip text.static final String LONG_DESCRIPTION
String
description for the action, could be used for context-sensitive help.static final String SMALL_ICON
Icon, such
as ImageIcon. This is typically used with
menus such as JMenuItem.
If the same Action is used with menus and buttons you'll
typically specify both a SMALL_ICON and a
LARGE_ICON_KEY. The menu will use the
SMALL_ICON and the button will use the
LARGE_ICON_KEY.
static final String ACTION_COMMAND_KEY
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.static final String ACCELERATOR_KEY
KeyStroke to be used as the
accelerator for the action.static final String MNEMONIC_KEY
Integer that corresponds to
one of the KeyEvent key codes. The value is
commonly used to specify a mnemonic. For example:
myAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_A)
sets the mnemonic of myAction to 'a'.static final String SELECTED_KEY
Boolean that corresponds
to the selected state. This is typically used only for components
that have a meaningful selection state. For example,
JRadioButton and JCheckBox make use of
this but instances of JMenu don't.
This property differs from the others in that it is both read
by the component and set by the component. For example,
if an Action is attached to a JCheckBox
the selected state of the JCheckBox will be set from
that of the Action. If the user clicks on the
JCheckBox the selected state of the JCheckBox
and the Action will both be updated.
Note: the value of this field is prefixed with 'Swing' to
avoid possible collisions with existing Actions.
static final String DISPLAYED_MNEMONIC_INDEX_KEY
Integer that corresponds
to the index in the text (identified by the NAME
property) that the decoration for a mnemonic should be rendered at. If
the value of this property is greater than or equal to the length of
the text, it will treated as -1.
Note: the value of this field is prefixed with 'Swing' to
avoid possible collisions with existing Actions.
AbstractButton.setDisplayedMnemonicIndex(int),
Constant Field Valuesstatic final String LARGE_ICON_KEY
Icon. This is typically
used by buttons, such as JButton and
JToggleButton.
If the same Action is used with menus and buttons you'll
typically specify both a SMALL_ICON and a
LARGE_ICON_KEY. The menu will use the
SMALL_ICON and the button the LARGE_ICON_KEY.
Note: the value of this field is prefixed with 'Swing' to
avoid possible collisions with existing Actions.
void putValue(String key, Object value)
PropertyChangeEvent is sent
to listeners.key - a String containing the keyvalue - an Object valuevoid setEnabled(boolean b)
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.b - true to enable this Action, false to disable itboolean isEnabled()
Action. When enabled,
any component associated with this object is active and
able to fire this object's actionPerformed method.Action is enabledvoid addPropertyChangeListener(PropertyChangeListener listener)
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.listener - a PropertyChangeListener objectvoid removePropertyChangeListener(PropertyChangeListener listener)
PropertyChange listener.listener - a PropertyChangeListener objectaddPropertyChangeListener(java.beans.PropertyChangeListener)