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java.lang.Object
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+--javax.microedition.lcdui.Displayable
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+--javax.microedition.lcdui.Screen
|
+--javax.microedition.lcdui.List
A Screen containing list of choices. Most of its
behavior is common with
class ChoiceGroup, and their common API. The
different List types in particular, are defined in
interface Choice. When a List is present on the display, the
user can interact with
it by selecting elements and possibly by traversing and scrolling among
them. Traversing and scrolling operations do not cause application-visible
events. The system notifies the application only when a Command is invoked by notifying its CommandListener. The
List
class also supports a select command that may be invoked specially
depending upon the capabilities of the device.
The notion of a select operation on a List
element is central
to the user's interaction with the List. On devices
that have a dedicated
hardware "select" or "go" key, the select
operation is implemented with
that key. Devices that do not have a dedicated key must provide another
means to do the select operation, for example, using a soft key. The
behavior of the select operation within the different types of lists is
described in the following sections.
List objects may be created with Choice types of
Choice.EXCLUSIVE, Choice.MULTIPLE, and
Choice.IMPLICIT. The Choice type Choice.POPUP
is not allowed on List objects.
EXCLUSIVE and MULTIPLE ListsThe select operation is not associated with a
Command object, so the
application has no means of setting a label for it or being notified when
the operation is performed. In Lists of type
EXCLUSIVE, the select
operation selects the target element and deselects the previously selected
element. In Lists of type MULTIPLE, the
select operation toggles the
selected state of the target element, leaving the selected state of other
elements unchanged. Devices that implement the select operation using a
soft key will need to provide a label for it. The label should be something
similar to "Select" for Lists of type
EXCLUSIVE, and it should be something
similar to "Mark" or "Unmark" for
Lists of type MULTIPLE.
IMPLICIT ListsThe select operation is associated with a Command
object referred to as
the select command. When the user performs the select operation,
the system will invoke the select command by notifying the
List's CommandListener. The default select command is the
system-provided command SELECT_COMMAND. The select
command may be modified
by the application through use of the setSelectCommand method. Devices that implement the select
operation using a soft key will use the label from the select command. If
the select command is SELECT_COMMAND, the device may
choose to provide its
own label instead of using the label attribute of
SELECT_COMMAND.
Applications should generally provide their own select command to replace
SELECT_COMMAND. This allows applications to provide a
meaningful label,
instead of relying on the one provided by the system for
SELECT_COMMAND.
The implementation must not invoke the select command if there are
no elements in the List, because if the
List is empty the selection does
not exist. In this case the implementation should remove or disable the
select command if it would appear explicitly on a soft button or in a menu.
Other commands can be invoked normally when the List
is empty.
IMPLICIT Lists IMPLICIT Lists can be used to
construct menus by providing operations
as List elements. The application provides a
Command that is used to
select a List element and then defines this
Command to be used as the
select command. The application must also register a
CommandListener that
is called when the user selects or activates the Command:
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The listener can query the List to determine which
element is selected
and then perform the corresponding action. Note that setting a command as
the select command adds it to the List as a side effect.
The select command should be considered as a default operation
that takes place when a select key is pressed. For example, a
List
displaying email headers might have three operations: read, reply, and
delete. Read is considered to be the default operation.
|
On a device with a dedicated select key, pressing this key will invoke
readCommand. On a device without a select key, the user is
still able to invoke the read command, since it is also provided as an
ordinary Command.
It should be noted that this kind of default operation must be used carefully, and the usability of the resulting user interface must always kept in mind. The default operation should always be the most intuitive operation on a particular List.
| Field Summary | |
static Command |
SELECT_COMMAND
The default select command for IMPLICIT Lists.
|
| Fields inherited from interface javax.microedition.lcdui.Choice |
EXCLUSIVE, IMPLICIT, MULTIPLE, POPUP, TEXT_WRAP_DEFAULT, TEXT_WRAP_OFF, TEXT_WRAP_ON |
| Constructor Summary | |
List(String title,
int listType)
Creates a new, empty List, specifying its title
and the type of the
list. |
|
List(String title,
int listType,
String[] stringElements,
Image[] imageElements)
Creates a new List, specifying its title, the type
of the List, and
an array of Strings and Images to be
used as its initial contents.
|
|
| Method Summary | |
int |
append(String stringPart,
Image imagePart)
Appends an element to the Choice. |
void |
delete(int elementNum)
Deletes the element referenced by elementNum.
|
void |
deleteAll()
Deletes all elements from this List. |
int |
getFitPolicy()
Gets the application's preferred policy for fitting Choice element
contents to the available screen space. |
Font |
getFont(int elementNum)
Gets the application's preferred font for rendering the specified element of this Choice. |
Image |
getImage(int elementNum)
Gets the Image part of the element referenced by
elementNum.
|
int |
getSelectedFlags(boolean[] selectedArray_return)
Queries the state of a Choice and returns the
state of all elements
in the
boolean array
selectedArray_return. |
int |
getSelectedIndex()
Returns the index number of an element in the Choice that is
selected. |
String |
getString(int elementNum)
Gets the String part of the element referenced by
elementNum.
|
void |
insert(int elementNum,
String stringPart,
Image imagePart)
Inserts an element into the Choice just prior to
the element specified.
|
boolean |
isSelected(int elementNum)
Gets a boolean value indicating whether this element is selected. |
void |
removeCommand(Command cmd)
The same as Displayable.removeCommand
but with the following additional semantics.
|
void |
set(int elementNum,
String stringPart,
Image imagePart)
Sets the String and Image parts of the
element referenced by elementNum,
replacing the previous contents of the element.
|
void |
setFitPolicy(int fitPolicy)
Sets the application's preferred policy for fitting Choice element
contents to the available screen space. |
void |
setFont(int elementNum,
Font font)
Sets the application's preferred font for rendering the specified element of this Choice.
|
void |
setSelectCommand(Command command)
Sets the Command to be used for an
IMPLICIT List selection
action.
|
void |
setSelectedFlags(boolean[] selectedArray)
Sets the selected state of all elements of the List. |
void |
setSelectedIndex(int elementNum,
boolean selected)
Sets the selected state of an element. |
int |
size()
Gets the number of elements in the List. |
| Methods inherited from class javax.microedition.lcdui.Displayable |
addCommand, getHeight, getTicker, getTitle, getWidth, isShown, setCommandListener, setTicker, setTitle, sizeChanged |
| Methods inherited from class java.lang.Object |
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
public static final Command SELECT_COMMAND
IMPLICIT Lists.
Applications using an IMPLICIT List
should set their own select command
using
setSelectCommand.
The field values of SELECT_COMMAND are:
- label = "" (an empty string)
- type = SCREEN
- priority = 0
(It would be more appropriate if the type were
ITEM, but the type of
SCREEN is retained for historical purposes.)
The application should not use these values for recognizing
the SELECT_COMMAND. Instead, object identities of
the Command and
Displayable (List) should be used.
SELECT_COMMAND is treated as an ordinary
Command if it is used with other Displayable
types.
| Constructor Detail |
public List(String title,
int listType)
List, specifying its title
and the type of the
list.
title - the screen's title (see Displayable)listType - one of IMPLICIT, EXCLUSIVE,
or MULTIPLE
IllegalArgumentException - if listType is not
one of
IMPLICIT,
EXCLUSIVE, or MULTIPLEChoice
public List(String title,
int listType,
String[] stringElements,
Image[] imageElements)
List, specifying its title, the type
of the List, and
an array of Strings and Images to be
used as its initial contents.
The stringElements array must be non-null and
every array element
must also be non-null. The length of the
stringElements array
determines the number of elements in the List.
The imageElements array
may be null to indicate that the List
elements have no images. If the
imageElements array is non-null, it must be the
same length as the
stringElements array. Individual elements of the
imageElements array
may be null in order to indicate the absence of an
image for the
corresponding List element. Non-null elements of the
imageElements array may refer to mutable or
immutable images.
title - the screen's title (see Displayable)listType - one of IMPLICIT, EXCLUSIVE,
or MULTIPLEstringElements - set of strings specifying the string parts of the
List elementsimageElements - set of images specifying the image parts of
the List elements
NullPointerException - if stringElements is
null
NullPointerException - if the stringElements
array contains any null elements
IllegalArgumentException - if the imageElements
array is non-null
and has a different length from the stringElements array
IllegalArgumentException - if listType is not one
of IMPLICIT,
EXCLUSIVE, or MULTIPLEChoice.EXCLUSIVE,
Choice.MULTIPLE,
Choice.IMPLICIT| Method Detail |
public int append(String stringPart,
Image imagePart)
ChoiceChoice. The added
element will be the last
element of the Choice. The size of the
Choice grows by one.
append in interface ChoicestringPart - the string part of the element to be addedimagePart - the image part of the element to be added,
or null if
there is no image part
public void delete(int elementNum)
ChoiceelementNum.
The size of the Choice shrinks by
one. It is legal to delete all elements from a Choice.
The elementNum parameter must be within the range
[0..size()-1], inclusive.
delete in interface Choicedelete in class ScreenelementNum - the index of the element to be deletedpublic void deleteAll()
deleteAll in interface ChoicedeleteAll in class Screenpublic int getFitPolicy()
Choice element
contents to the available screen space. The value returned is the
policy that had been set by the application, even if that value had
been disregarded by the implementation.
getFitPolicy in interface ChoiceChoice.TEXT_WRAP_DEFAULT, Choice.TEXT_WRAP_ON, or
Choice.TEXT_WRAP_OFFsetFitPolicy(int)public Font getFont(int elementNum)
Choice. The
value returned is the font that had been set by the application,
even if that value had been disregarded by the implementation.
If no font had been set by the application, or if the application
explicitly set the font to null, the value is the default
font chosen by the implementation.
The elementNum parameter must be within the range
[0..size()-1], inclusive.
getFont in interface ChoiceelementNum - the index of the element, starting from zero
IndexOutOfBoundsException - if elementNum is invalidsetFont(int elementNum, Font font)public Image getImage(int elementNum)
ChoiceImage part of the element referenced by
elementNum.
The elementNum parameter must be within the range
[0..size()-1], inclusive.
getImage in interface ChoiceelementNum - the index of the element to be queried
null
if there is no imageChoice.getString(int)public int getSelectedFlags(boolean[] selectedArray_return)
ChoiceChoice and returns the
state of all elements
in the
boolean array
selectedArray_return. Note: this
is a result parameter.
It must be at least as long as the size
of the Choice as returned by size().
If the array is longer, the extra
elements are set to false.
This call is valid for all types of
Choices. For MULTIPLE, any
number of elements may be selected and set to true
in the result
array. For EXCLUSIVE, POPUP, and
IMPLICIT
exactly one element will be selected (unless there are
zero elements in the Choice).
getSelectedFlags in interface ChoiceselectedArray_return - array to contain the results
ChoiceChoice.setSelectedFlags(boolean[])public int getSelectedIndex()
ChoiceChoice that is
selected. For
Choice types EXCLUSIVE,
POPUP, and IMPLICIT
there is at most one element selected, so
this method is useful for determining the user's
choice. Returns -1 if
the Choice has no elements (and therefore has no
selected elements).
For MULTIPLE, this always returns
-1 because no single
value can in general represent the state of such a Choice.
To get the complete state of a MULTIPLE Choice,
see getSelectedFlags.
getSelectedIndex in interface Choice-1 if noneChoice.setSelectedIndex(int, boolean)public String getString(int elementNum)
ChoiceString part of the element referenced by
elementNum.
The elementNum parameter must be within the range
[0..size()-1], inclusive.
getString in interface ChoiceelementNum - the index of the element to be queried
Choice.getImage(int)
public void insert(int elementNum,
String stringPart,
Image imagePart)
ChoiceChoice just prior to
the element specified.
The size of the Choice grows by one.
The elementNum parameter must be within the range
[0..size()], inclusive. The index of the last
element is size()-1, and
so there is actually no element whose index is
size(). If this value
is used for elementNum, the new element is
inserted immediately after
the last element. In this case, the effect is identical to
append().
insert in interface ChoiceelementNum - the index of the element where insertion is to occurstringPart - the string part of the element to be insertedimagePart - the image part of the element to be inserted,
or null if there is no image partpublic boolean isSelected(int elementNum)
ChoiceelementNum parameter must be within the range
[0..size()-1], inclusive.
isSelected in interface ChoiceelementNum - the index of the element to be queried
public void removeCommand(Command cmd)
Displayable.removeCommand
but with the following additional semantics.
If the command to be removed happens to be the select command, the
List is set to have no select command, and the command is
removed from the List.
The following code:
|
is equivalent to the following code:
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removeCommand in class Displayablecmd - the command to be removedCommandpublic void setSelectedFlags(boolean[] selectedArray)
List.
setSelectedFlags in interface ChoiceselectedArray - an array in which the method collect
the selection status
IllegalArgumentException - if selectedArray is
shorter than the size of the List
NullPointerException - if selectedArray is
nullgetSelectedFlags(boolean[])
public void set(int elementNum,
String stringPart,
Image imagePart)
ChoiceString and Image parts of the
element referenced by elementNum,
replacing the previous contents of the element.
The elementNum parameter must be within the range
[0..size()-1], inclusive. The font attribute of
the element is left unchanged.
set in interface ChoiceelementNum - the index of the element to be setstringPart - the string part of the new elementimagePart - the image part of the element, or
null if there is
no image partpublic void setFitPolicy(int fitPolicy)
Choice element
contents to the available screen space. The set policy applies for all
elements of the Choice object. Valid values are
Choice.TEXT_WRAP_DEFAULT, Choice.TEXT_WRAP_ON,
and Choice.TEXT_WRAP_OFF. Fit policy is a hint, and the
implementation may disregard the application's preferred policy.
setFitPolicy in interface ChoicefitPolicy - preferred content fit policy for choice elements
IllegalArgumentException - if fitPolicy is invalidgetFitPolicy()
public void setFont(int elementNum,
Font font)
Choice.
An element's font is a hint, and the implementation may disregard
the application's preferred font.
The elementNum parameter must be within the range
[0..size()-1], inclusive.
The font parameter must be a valid Font
object or null. If the font parameter is
null, the implementation must use its default font
to render the element.
setFont in interface ChoiceelementNum - the index of the element, starting from zerofont - the preferred font to use to render the element
IndexOutOfBoundsException - if elementNum is invalidgetFont(int)public void setSelectCommand(Command command)
Command to be used for an
IMPLICIT List selection
action.
By default, an implicit selection of a List will result in the
predefined List.SELECT_COMMAND being used. This
behavior may be
overridden by calling the List.setSelectCommand()
method with an
appropriate parameter value. If a null reference
is passed, this
indicates that no "select" action is appropriate for
the contents
of this List.
If a reference to a command object is passed, and
it is not the special command List.SELECT_COMMAND, and
it is not currently present on this List object,
the command object is added to this List as if
addCommand(command) had been called
prior to the command being made the select command. This
indicates that this command
is to be invoked when the user performs the "select"
on an element of
this List.
The select command should have a command type of
ITEM to indicate
that it operates on the currently selected object. It is not an error
if the command is of some other type.
(List.SELECT_COMMAND has a type
of SCREEN for historical purposes.) For purposes
of presentation and
placement within its user interface, the implementation is allowed to
treat the select command as if it were of type ITEM.
If the select command is later removed from the List with
removeCommand(), the List's select
action behavior reverts to its
default behavior of using List.SELECT_COMMAND as
the select command.
The default behavior can be reestablished explicitly by calling
setSelectCommand() with an argument of
List.SELECT_COMMAND.
This method has no effect if the type of the
List is not IMPLICIT.
command - the command to be used for an IMPLICIT list
selection action, or null if there is none
public void setSelectedIndex(int elementNum,
boolean selected)
setSelectedIndex in interface ChoiceelementNum - the index of the element, starting from zeroselected - the state of the element, where true means
selected and false means not selected
IndexOutOfBoundsException - if elementNum is invalidgetSelectedIndex()public int size()
List.
size in interface ChoiceList
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