Responding to Keyboard Input

parent InputMap

· ·

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3.6.1.2 Constructor

public InputMap( )

The default constructor is the only constructor available. It creates an empty

InputMap

with no

parent

.

3.6.1.3 Methods

public KeyStroke[] allKeys( )

Return an array of all

KeyStroke

s defined in the

InputMap

, either directly or anywhere along the

parent

chain. If there are no mappings, this method returns either an empty array or

null

, depending on the history of the

InputMap

(s). Each key appears only once even if it overrides another on the parent chain.

public void clear( )

Remove all keystroke mappings from this

InputMap

(does not affect any mappings in the

parent

chain).

public Object get(KeyStroke keyStroke)

Look up the specified

keyStroke

in the

InputMap

(and the

parent

chain), returning a value that represents the logical action that should be taken in response. If no match is found, returns

null

. The result is generally used immediately to look up an

Action

in the

ActionMap

of the component that owns this

InputMap

. Convention dictates that the values returned are

String

s describing the nature of the action to perform.

public KeyStroke[] keys

Return an array of

KeyStroke

s locally defined in this

InputMap

. That is to say, it does not follow the

parent

chain. If there are no mappings, this returns either an empty array or

null

, depending on the history of the

InputMap

.

public void put(KeyStroke keyStroke, Object actionMapKey)

Define a new mapping for the specified

keyStroke

. Future calls to the

get( )

method return

actionMapKey

as the logical action associated with

keyStroke

. As suggested by the parameter name,

actionMapKey

is

intended to be used to look up an

Action

in an

ActionMap

. By convention, it should be a

String

whose value is descriptive of the action. (Appendix B lists the standard

ActionMap

keys supported by Swing components; your own classes can use these or define their own as appropriate.) Passing a

null actionMapKey

has the same effect as calling

remove(keyStroke)

.

public void remove(KeyStroke keyStroke)

Remove the mapping defined for the specified

keyStroke

from this

InputMap

. Looking up that

keyStroke

in the future returns a value that is determined by the

parent

chain (which is not affected by this method). If you want to "block" a mapping in a shared

InputMap

that is part of your

parent

chain, define a mapping for that

KeyStroke

to the string

none

. By convention, there is never an

Action

associated with

none

in any

ActionMap

, so its presence in your

InputMap

causes the

parent

check to be skipped without allowing any action to take place.

public int size( )

Return the number of mappings defined in this

InputMap

(not counting any that might be defined in the

parent

chain). For a new or newly cleared

InputMap

, this returns

0

.

3.6.2 The ActionMap Class

ActionMap

is responsible for mapping logical action names to concrete

Action

instances that carry them out. When the user types a key combination, it's looked up in the

InputMap

of a component, and the result is looked up as a key in the corresponding

ActionMap

.

Although any object can be used as a key in an

ActionMap

, in practice they are

String

s. By convention, their content is a descriptive name for the action to be performed (such as

copy

,

print

,

save

, or the like), often obtained by calling

getName( )

on the corresponding

Action

.

ActionMap

s can be chained together so that common functionality can be shared in a basic

ActionMap

; specialized components can add unique actions to their own

ActionMap

and delegate the common cases to the shared map through the

parent

property.

A component's

ActionMap

can also be used to configure auditory cues to be played at appropriate points by the component, as described in Chapter 26.

3.6.2.1 Property

The single property defined by

ActionMap

is shown in Table 3-11. The

parent

property establishes a fallback

ActionMap

that is consulted if an action name is not found in the current map, much as the inheritance chain is followed when looking up the members of Java classes. If you create a cycle in the

parent

chain (for example, by setting two

ActionMaps

to be

parent

s of each other), many of the method calls crash with a

StackOverflowError

.

Table 3-11. ActionMap property

Property Data type get is set Default value

parent ActionMap

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3.6.2.2 Constructor

public ActionMap( )

The default constructor is the only constructor available. It creates an empty

ActionMap

with no

parent

.

3.6.2.3 Methods

public Object[] allKeys( )

Return an array of all logical action names defined in the

ActionMap

, either directly or anywhere along the

parent

chain. If there are no mappings, this method returns either an empty array or

null

, depending on the history of the

ActionMap

(s). Each key appears only once even if it overrides another on the parent chain.

public void clear( )

Remove all action mappings from the local

ActionMap

(does not affect any in the

parent

chain).

public Action get(Object key)

Look up the specified action name in the

ActionMap

(and the

parent

chain), returning the corresponding

Action

to be executed. If no match is found, returns

null

. The keys are often obtained by looking up a

KeyStroke

in an

InputMap

.

public Object[] keys

Return an array of the logical action names locally defined in this

ActionMap

. That is to say, it does not follow the

parent

chain. If there are no mappings, this returns either an empty array or

null

, depending on the history of the

ActionMap

.

public void put(Object key, Action action)

Define a new mapping for the specified

action

. Future calls to the

get( )

method return it as the

Action

associated with the logical name

key

. By convention,

key

should be a

String

whose value is descriptive of the action. Appendix B lists the standard

ActionMap

keys supported by Swing components; your own classes can use these as well, or define their own, as appropriate. Passing a

null key

has the same effect as calling

remove(action)

.

public void remove(Object Key)

Remove the mapping defined for the specified

key

from this

ActionMap

. Looking up that logical action name in the future returns a value determined by the

parent

chain (which is not affected by this method).

public int size( )

Return the number of mappings defined in this

ActionMap

(not counting any that might be defined in the

parent

chain). For a new or newly cleared

ActionMap

, this method returns

0

.

I l@ve RuBoard

I l@ve RuBoard

在文檔中 Java™ Swing, 2nd Edition (頁 115-120)