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Choice defines an API for a user interface components implementing
selection from predefined number of choices. Such UI components are
List
and ChoiceGroup
.
The contents of the Choice are represented
with strings and optional images.
Each element of a Choice is composed of a static text string and an
optional image. The application may provide null
for the
image if the element does not have an image part. If the application
provides an image, the implementation may choose to ignore the image if it
exceeds the capacity of the device to display it. If the implementation
displays the image, it will be displayed adjacent to the text string and
the pair will be treated as a unit.
If an element is too long to be displayed on one line it wraps onto multiple lines to fit the width of the display. When an element wraps to multiple lines, the second and subsequent lines show a clear indication to the user that they are part of the same element and are not a new element. For example, the second and subsequent lines may be shown indented.
There are three types of Choices: implicit-choice (valid only for
List
), exclusive-choice,
and multiple-choice.
The exclusive-choice presents a series of elements and interacts with the user in object-action mode. That is, when the user selects an element, that element is shown to be selected using a distinct visual representation. Exactly one element must be selected at any given time. If at any time a situation would result where there are elements in the exclusive-choice but none is selected, the implementation will choose an element and select it. This situation can arise when an element is added to an empty Choice, or when the selected element is deleted from the Choice. There is no way for the user to unselect an element within an Exclusive Choice.
The implicit choice is an exclusive choice where the focused element is implicitly selected when a command is initiated.
A multiple-choice presents a series of elements and allows the user to select any number of elements in any combination. As with exclusive-choice, the multiple-choice interacts with the user in object-operation mode. The visual appearance of a multiple-choice will likely have a visual representation distinct from the exclusive-choice that shows the selected state of each element as well as indicating to the user that multiple elements may be selected.
When a Choice is present on the display the user can interact with it
indefinitely (for instance, traversing from element to element
and possibly
scrolling). These traversing and scrolling operations do not cause
application-visible events. The system notifies
the application either when some application-defined
Command
is fired, or when selection state of
ChoiceGroup
is changed.
When command is fired
a high-level event is delivered to the listener of the Screen.
The event delivery is done with
commandAction
.
In the case of ChoiceGroup
the
ItemStateListener
is called
when the user changes the selection state of the ChoiceGroup.
At this time the application can query the Choice for
information about the currently selected element(s).
The implementation may have keyboard shortcuts for focusing and selecting the choice elements, but the use of these shortcuts is not visible to the application program.
Field Summary | |
static int |
EXCLUSIVE
EXCLUSIVE is a choice having exactly one element selected at time. |
static int |
IMPLICIT
IMLICIT is a choice in which the currently focused item is selected when a Command is initiated. |
static int |
MULTIPLE
MULTIPLE is a choice that can have arbitrary number of elements selected at a time. |
Method Summary | |
int |
appendElement(String stringPart,
Image imagePart)
Appends an element to the Choice. |
void |
deleteElement(int elementNum)
Deletes the element referenced by elementNum. |
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. |
int |
getSize()
Gets the number of elements present in the Choice. |
String |
getString(int elementNum)
Gets the String part of the element referenced by elementNum. |
void |
insertElement(int elementNum,
String stringPart,
Image imagePart)
Inserts an element into the Choice just before to the element specified. |
boolean |
isSelected(int elementNum)
Gets a boolean value indicating whether this element is selected. |
void |
setElement(int elementNum,
String stringPart,
Image imagePart)
Sets the element referenced by elementNum to the specified element, replacing the previous contents of the element. |
void |
setSelectedFlags(boolean[] selectedArray)
Attempts to set the selected state of every element in the Choice. |
void |
setSelectedIndex(int elementNum,
boolean selected)
For MULTIPLE, this simply sets an individual element's selected state. |
Field Detail |
public static final int EXCLUSIVE
Value 1 is assigned to EXCLUSIVE.
public static final int MULTIPLE
Value 2 is assigned to MULTIPLE.
public static final int IMPLICIT
Command
is initiated.
(Note: IMPLICIT is not accepted by
ChoiceGroup
)
Value 3 is assigned to IMPLICIT.
Method Detail |
public int getSize()
public String getString(int elementNum)
elementNum
- the number of the elementgetImage(int)
public Image getImage(int elementNum)
elementNum
- the number of the elementgetString(int)
public int appendElement(String stringPart, Image imagePart)
stringPart
- 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 partpublic void insertElement(int elementNum, String stringPart, Image imagePart)
elementNum
- the number of the elementstringPart
- 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 void deleteElement(int elementNum)
elementNum
- the number of the element to be deletedpublic void setElement(int elementNum, String stringPart, Image imagePart)
elementNum
- the number of the elementstringPart
- the string part of the new elementimagePart
- the image part of the element, or null if there is
no image partpublic boolean isSelected(int elementNum)
elementNum
- index to element of interestpublic int getSelectedIndex()
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
.
public int getSelectedFlags(boolean[] selectedArray_return)
selectedArray_return
- array to contain the results.
It must be at least as long as the size
of the Choice as returned by getSize().
If the array is longer, the extra
elements are set to false.public void setSelectedIndex(int elementNum, boolean selected)
For MULTIPLE, this simply sets an individual element's selected state.
For EXCLUSIVE,
this can be used only to select any
element, that is, the selected
parameter must be
true
. When an element is selected, the previously selected element
is deselected. If selected
is false
, this
call is ignored.
For IMPLICIT,
this can be used only to select any
element, that is, the selected
parameter must be
true
. When an element is selected, the previously selected element
is deselected. If selected
is false
, this
call is ignored.
The call to setSelectedIndex does not cause implicit activation of
any Command.
elementNum
- the number of the element. Indexing of the elements is zero-based.selected
- the new state of the element true=selected, false=not selected.public void setSelectedFlags(boolean[] selectedArray)
For Choice objects of type MULTIPLE, this sets the selected state of every element in the Choice. An arbitrary number of elements may be selected.
For Choice objects of type EXCLUSIVE and IMPLICIT, exactly one array element must have the value true. If no element is true, the first element in the Choice will be selected. If two or more elements are true, the implementation will choose the first true element and select it.
selectedArray
- an array in which the method collect the selection status
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