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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 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.
Images within any particular Choice object should all be of the same size, because the implementation is allowed to allocate the same amount of vertical space for every element.
If an element is too long to be displayed, the implementation will provide the user with means to see the whole element. If this is done by wrapping an element 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.
After a Choice object has been created, elements may be inserted, appended, and deleted, and each element's string part and image part may be get and set. Elements within a Choice object are referred to by their indexes, which are consecutive integers in the range from zero to size()-1, with zero referring to the first element and size()-1 to the last element.
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. 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, when the selected element is deleted from the Choice, or when a Choice is created and populated with elements by a constructor. In these cases, the choice of which element is selected is left to the implementation. Applications for which the selected element is significant should set the selection explicitly. 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.
The selected state of an element is a property of the element. This state stays with that element if other elements are inserted or deleted, causing elements to be shifted around. For example, suppose element n is selected, and a new element is inserted at index zero. The selected element would now have index n+1. A similar rule applies to deletion. Assuming n is greater than zero, deleting element zero would leave element n-1 selected. Setting the contents of an element leaves its selected state unchanged. When a new element is inserted or appended, it is always unselected (except in the special case of adding an element to an empty Exclusive Choice as mentioned above).
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).
| Field Summary | |
static int |
EXCLUSIVE
EXCLUSIVE is a choice having exactly one element selected at time. |
static int |
IMPLICIT
IMPLICIT 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 |
append(String stringPart,
Image imagePart)
Appends an element to the Choice. |
void |
delete(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. |
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 |
set(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. |
int |
size()
Gets the number of elements present. |
| 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 size()
Gets the number of elements present.
public String getString(int elementNum)
Gets the String part of the element referenced by elementNum. The elementNum parameter must be within the range [0..size()-1], inclusive.
elementNum - the index of the element to be queriedgetImage(int)public Image getImage(int elementNum)
Gets the Image part of the element referenced by elementNum. The elementNum parameter must be within the range [0..size()-1], inclusive.
elementNum - the index of the element to be queriedgetString(int)
public int append(String stringPart,
Image imagePart)
Appends an element to the Choice. The added element will be the last element of the Choice. The size of the Choice grows by one.
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 part
public void insert(int elementNum,
String stringPart,
Image imagePart)
Inserts an element into the Choice 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().
elementNum - 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 void delete(int elementNum)
Deletes the element referenced by elementNum. 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.
elementNum - the index of the element to be deleted
public void set(int elementNum,
String stringPart,
Image imagePart)
Sets the element referenced by elementNum to the specified element, replacing the previous contents of the element. The elementNum parameter must be within the range [0..size()-1], inclusive.
elementNum - 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 boolean isSelected(int elementNum)
Gets a boolean value indicating whether this element is selected. The elementNum parameter must be within the range [0..size()-1], inclusive.
elementNum - the index of the element to be queriedpublic int getSelectedIndex()
Returns the index number of an element in the Choice that is selected. For Choice types EXCLUSIVE 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.
public int getSelectedFlags(boolean[] selectedArray_return)
Queries the state of a Choice 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 and IMPLICIT exactly one element will be selected (unless there are zero elements in the Choice).
selectedArray_return - array to contain the results
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. If element was already selected, the call has no effect.
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. If element was already selected, the call has no effect.
The call to setSelectedIndex does not cause implicit activation of any Command.
For all list types, the elementNum parameter must be within the range [0..size()-1], inclusive.
elementNum - the index of the element, starting from zeroselected - the state of the element, where true means
selected and false means not selectedpublic void setSelectedFlags(boolean[] selectedArray)
Attempts to set the selected state of every element in the Choice. The array must be at least as long as the size of the Choice. If the array is longer, the additional values are ignored.
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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