A
JList
is the interface to the Java Swing JList Component.
Yoix programs normally interact with a
JList
using event handlers and by reading or writing the following fields:
| background |
The
Color
that is used to paint the background of the list.
Reading returns a snapshot of the current color.
Writing immediately changes the background to the new color.
Storing
NULL
in
background
is special and means the list uses its preferred color, which is white.
| | border |
An
Object
that should be a
Border,
Insets,
Number,
or
String
that describes the border that is drawn around this list.
A
NULL
value, which is the default, means no border.
A
border
that is an
Insets
or
Number
is an easy way to describe margins
(i.e., an
EmptyBorder),
in units of 72 dots per inch, that are left around the sides of this list.
A
border
that is a
String
is a quick way to surround this list with a border that uses the
String
as its title.
Reading returns a snapshot of the current border.
Writing immediately sets the list's border to the new value.
| | columns |
An
int
that specifies the number of columns that you want in the list.
Layout managers usually get the final say, so setting
columns
should be viewed as a request that will not always be honored.
The value should be zero, which is the default, when you want
the list's width reference to be determined by the
items
loaded in the list.
| | cursor |
An
Object
that should be an
int,
Image,
or
String
that selects the cursor shown when the pointer is over the list.
A
cursor
that is an
int
should be one of the cursors defined in the
yoix.awt.Cursor
dictionary.
A
cursor
that is an
Image
can describe the cursor using its
size
and
hotspot
fields and often draws it using its
paint
function.
A
cursor
that is a
String
should be the name of a cursor that is already defined in
yoix.awt.Cursor
or the name a local a file or URL that contains a GIF or JPEG image
that will be used as the cursor.
Reading returns the current cursor.
Writing immediately changes the list's cursor to the new value.
Storing
STANDARD_CURSOR
(the default) or
NULL
in
cursor
is special and means use the cursor assigned to the nearest component
that contains the list and was assigned a cursor other than
STANDARD_CURSOR;
if no component qualifies the list uses
DEFAULT_CURSOR.
| | doublebuffered |
An
int
that is
1
when the list uses double-buffering to draw itself,
0
when it does not, and starts with a default value that is
selected by Java for the list.
Reading returns the current double-buffering behavior.
Writing immediately sets the list's double-buffering behavior to the new value.
Note that double-buffering may be required when transparent components are used.
| | dragenabled |
An
int
that should be set to
1
when this list wants to use the automatic drag handling that Swing provides
for some components, and
0
(the default)
when it does not.
Components that do not provide automatic drag handling always return
0
when their
dragenabled
field is read, so storing
1
in
dragenabled
should only be viewed as a request for a service that may not be available.
Swing components can always take complete control of their drag and drop
handling using their
transferhandler
field or special drag and drop event handlers.
| | enabled |
An
Object
that is
1
when the list can respond to user input,
0
when it can not respond, and
NULL
(the default)
when the list inherits the value from the nearest lightweight container,
like a
JPanel,
that contains the list and has its
enabled
field set to something other than
NULL.
The top-level application window that contains the list always gets the
final say, so disabling that window always disables the list.
Reading returns the current state.
Writing immediately sets the list's state to the new value.
| | focusable |
An
int
that is non-zero (the default)
when the list can accept the keyboard focus and zero
when it can not.
Reading returns the list's current focusable state.
Writing immediately changes the list's focusable state to the new value,
which means the focus is automatically transferred if the new value is zero
and the list is the current focus owner.
| | focusowner |
A read-only
int
that is non-zero when the list has the focus.
| | font |
The
Font,
or font name if it is a
String,
used to paint the text strings displayed by the list.
Reading returns a snapshot of the current font.
Writing immediately repaints the text strings displayed by the list
in the new font.
| | foreground |
The
Color
that is used to paint text strings displayed by the list.
Reading returns a snapshot of the current color.
Writing immediately repaints the text strings displayed by the list
in the new color.
Storing
NULL
in
foreground
is special and means use the foreground of the nearest component
that contains the list and was assigned a foreground color other than
NULL;
if no component qualifies the list uses
VM.screen.foreground.
| | index |
An
int
that can be used to adjust the view of the list.
Writing tries to reposition the list so the specified item is visible.
Reading usually provides the last number stored in
index,
which unfortunately is not particularly useful because the value
may have no relationship to the items that are currently visible.
| | items |
An
Array
of strings, usually organized in pairs, that determines what is loaded
in the list (i.e., what users see) and what is returned by
the list when reading the
selected
field.
Strings at even indices in
items
are loaded in the list;
strings at odd indices are return values.
A
NULL
at an odd index means the return value is the string at the
corresponding even index
(i.e., the one that was loaded in the list).
The grouping has to be changed slightly if you want to display images in the list.
The change happens automatically when the first element in
items
is
NULL
or an
Image
(actually anything other than a
String)
and in that case the elements in the array are assumed to be organized in triples with the
Image
being the first element, the text string displayed by the list the second element,
and the value returned when
selected
is read the third element.
Setting this field to
NULL
clears the list completely.
Reading this value will always return an
Array
of at least size 0.
This field affects the values of the
labels
and
mappings
fields (and vice versa).
| | labels |
An
Array
of strings that determines what is loaded
in the list and what is returned by
the list when reading the
selected
field.
All the strings are loaded into the list and the same values are returned
in the
selected
field.
The result is equivalent to using the
items
field with alternating
NULL
values.
Setting this field to
NULL
clears the list completely.
Reading this value will always return an
Array
of at least size 0.
This field affects the values of the
items
and
mappings
fields.
| | layer |
An
int,
often a small number between 0 and 99,
that identifies the depth of this list when it is added to a
JLayeredPane
or
JDesktopPane.
Components assigned to lower numbered layers are drawn before
the components in higher numbered layers.
Writing immediately changes the list's layer, which usually means the
JLayeredPane
or
JDesktopPane
that contains the list will be repainted.
| | location |
A
Point
that determines the location of the list
in a coordinate system that has its origin at the upper left corner
of the container closest to the list (in the component hierarchy)
that actually contains it, positive x to the right, positive y down,
and a resolution of 72 dots per inch.
Reading returns a snapshot of the current location.
Writing is allowed, but layout managers usually get the final say, so setting
location
should be viewed as a request that may not be honored.
| | mappings |
An
Array
of strings that determines what is returned by
the list when reading the
selected
field.
This field must be set after the
labels
or
items
field is set and the length of the
Array
must match the length of the
Array
returned by the
labels
field.
The strings are assigned to be the return values for corresponding element,
positionally, in the labels
Array.
This field can be used to replace existing mappings, even those set by the
items
field.
Setting this field to
NULL
is equivalent to using the
items
field with alternating
NULL
values or the
labels
field alone.
Reading this value will always return an
Array
of at least size 0.
| | multiplemode |
An
int
that is
1
when more than one item can be selected, and
0
otherwise.
Reading returns the current mode.
Writing immediately sets a new mode, which may also mean deselecting
all but one of the currently selected items.
| | nextfocus |
An
Object
that identifies the component that receives the focus after this list
when the focus traverses from one component to the next
(usually by means of the keyboard
TAB
character).
When
nextfocus
is a
String
it is assumed to be the tag associated with the target component,
which must belong to the same top-level container (e.g., the same
JFrame)
as this list.
A
NULL
value means the component that gets the focus after this list will be
selected by Java's default focus traversal policy.
Reading returns the value last stored or
NULL
if the value was a
String
that did not reference a component.
Writing immediately changes the component that gets the focus after this list.
| | opaque |
An
Object
that is
1
when the list is opaque,
0
when it is transparent, and
NULL
(the default)
when the list inherits the value from the nearest component that
contains the list and has its
opaque
field set to something other than
NULL.
| | popup |
A
JPopupMenu
that is associated with the list.
Reading returns the current popup menu.
Writing immediately shows the popup menu at the point in the list's coordinate
system specified by the popup menu's
location
field, assuming of course that the list is showing on the screen.
Storing
TRUE
in the popup menu's
visible
field, which was added in release 1.2.0, is an easy way to show the
popup menu that currently belongs to the list.
| | preferredsize |
A
Dimension
that is used by layout managers when they need to know the list's
preferred size in units of 72 dots per inch.
A
NULL
value means the list has no preference.
A non-positive height or width is allowed and simply means the list
has no preference for that dimension.
Reading returns the current preferred size.
Writing changes the preferred size and immediately notifies
root.layoutmanager,
which means the components contained in
root
may be repositioned and resized.
| | prototypevalue |
An
Object,
usually a
String,
that Swing can use to compute the maximum width and height the cells displayed
by the list.
A value of
NULL,
which is the default, means all items displayed by the list are measured
and used to calculate the appropriate cell width and height.
A value that's the empty string (i.e.,
"")
is special and means all text strings that can be displayed by the list
are measured once and the widest one is handed to Swing as the prototype.
Even though all strings are measured, it only happens once, so in practice
the empty string really does turn out to be a reasonable choice.
| | requestfocus |
An
int
that can be used to request or transfer the keyboard focus.
Storing a non-zero value in
requestfocus
tries to get the focus.
Storing
0
tries to transfer the focus.
Reading
requestfocus
does not currently return any useful information.
| | requestfocusenabled |
An
int
that is
1
(the default)
when actions, like mouse clicks or changes to the
requestfocus
field, can steal the keyboard focus and
0
when they can not.
Note that this field does not affect acceptance of the keyboard focus
during normal focus traversal.
Reading returns the current state.
Writing immediately sets the list's state to the new value.
| | root |
An
Object
that is automatically updated by the interpreter's layout machinery
so it is always the top-level object that contains the list.
For example, put a list in a panel and
root
will be set to that panel;
add the panel to a frame and the list's
root
field will be set to that frame.
A list's event handlers can use
root
when they need to interact with the other components in the container.
| | rows |
An
int
that specifies the number of rows in a new list.
Layout managers usually get the final say, so setting
rows
should be viewed as a request that will not always be honored.
Changing
rows
after a list has been created has no effect and eventually may
trigger an
invalidaccess
error.
| | scroll |
An
int
that controls how scrollbars are added to a new list.
The value should normally be one of
NONE,
HORIZONTAL,
VERTICAL,
BOTH,
or
AS_NEEDED
(the default), which are all defined in
yoix.swing.
Fancier controls described in the
JScrollPane
reference page are allowed here, but in practice they are rarely needed.
In addition you can explicitly set
scroll
to zero to permanently disable scrolling in this list.
| | selected |
A
String,
int,
or
Array
of strings and integers that refer to the items currently selected
by the list.
Reading always returns an array of strings that correspond to
the currently selected items:
the array is empty, but not
NULL,
when no items are selected.
Storing an integer in
selected
picks the item at that index.
Storing a string in
selected
picks the item that has that string as its return value,
or if there is no match, the item that has that string as its actual value.
Storing an array of strings or integers in
selected
is how you set several items in a
multiplemode
list.
The selected items in a list are cleared when
NULL
is assigned to
selected.
| | selectedindex |
A read-only
int
that is the smallest index of the selected items or
-1
when no items are selected.
| | selectedlabel |
A read-only
Array
of strings that are the labels of the currently selected items
in the list.
The array is empty, but not
NULL,
when no items are selected.
When no
mapping
is in effect, it returns the same value as
selected.
| | showing |
A read-only
int
that is non-zero when the list is showing on the screen.
| | size |
A
Dimension
that determines the size of the list
in units of 72 dots per inch.
Reading returns a snapshot of the current size.
Writing is allowed, but layout managers usually get the final say, so setting
size
should be viewed as a request that may not be honored.
| | tag |
A
String
used to identify the list that is either supplied when
the list is declared, or automatically generated otherwise.
Add a list to a container, like a
JFrame
or
JPanel,
and the interpreter's layout machinery updates the
root
field so it points at the top-level container and then adds the list, as
tag,
to the
root.components
dictionary.
| | tooltiptext |
A
String
of characters that is displayed in a tightly sized pop-up window that
appears near the cursor whenever the cursor lingers over the list.
Setting this value to
NULL
(the default)
disables the tooltip mechanism.
Reading returns the current tooltip text.
Writing immediately sets the new tooltip text.
| | transferhandler |
An
Object
that should be a
TransferHandler
or
String
that determines how the list handles data transfer operations
like drag and drop.
A value that is a
String
but not
""
means the field named by the
String
should be used as the source and sink of the data that is transferred by
the list.
The result is the same as assigning the
String
to the
property
field in a
TransferHandler
and then assigning that
TransferHandler
to
transferhandler.
The empty
String
""
is special and refers to the
TransferHandler
that Swing uses for automatic drag handling, if there is one.
Swing components that provide automatic drag handling start out with a
transferhandler
field that is not
NULL,
but the automatic drag handling is not enabled until
1
is stored in
dragenabled.
Swing components that provide their own drag and drop event handlers
currently must store
NULL
in
transferhandler
before those event handlers will start working.
| | visible |
An
int
that is
1
when the list is visible, and
0
otherwise.
Reading returns the current visibility.
Writing immediately sets the list's visibility to the new state.
|
Several permanent fields have not been documented and should not be
used in Yoix applications.
Event handlers are functions that must be added to a list when it is
declared.
The handlers that work with lists are listed below;
the names should be familiar if you have done some Java programming.
The
actionPerformed
and
itemStateChanged
event handlers are only for menus.
| |
| Event Handlers: |
actionPerformed,
adjustmentValueChanged,
componentHidden,
componentMoved,
componentResized,
componentShown,
dragDropEnd,
dragEnter,
dragExit,
dragGestureRecognized,
dragMouseMoved,
dragOver,
drop,
dropActionChanged,
focusGained,
focusLost,
invocationRun,
itemStateChanged,
keyPressed,
keyReleased,
keyTyped,
mouseClicked,
mouseDragged,
mouseEntered,
mouseExited,
mouseMoved,
mousePressed,
mouseReleased,
mouseWheelMoved,
valueChanged
| | |
| Example: |
The program,
import yoix.*.*;
JFrame f = {
FlowLayout layoutmanager = {
int hgap = 10;
int vgap = 72;
};
Array layout = {
new JList {
Array items = {
"one", "1",
"two", NULL,
"three", "3",
"four", NULL,
"five", "5"
};
int rows = 2;
int multiplemode = 1;
valueChanged(ListSelectionEvent e) {
if (!e.sequence)
printf("selected=%O\n", selected);
}
},
new JList {
Array items = {" ", NULL, "Continue", NULL, "Quit", NULL};
int selected = 1;
valueChanged(ListSelectionEvent e) {
if (!e.sequence) {
printf("selected=%O\n", selected);
if (strcmp(selected[0], "Quit") == 0)
exit(0);
}
}
},
};
};
f.visible = TRUE;
adds two lists to a frame,
prints the selected value when either one is changed,
and quits when the last item in the right list is
selected.
| | |
| See Also: |
BevelBorder,
Border,
EmptyBorder,
EtchedBorder,
invokeLater,
JButton,
JCanvas,
JCheckBox,
JCheckBoxMenuItem,
JChoice,
JColorChooser,
JComboBox,
JDesktopPane,
JDialog,
JFileChooser,
JFileDialog,
JFrame,
JInternalFrame,
JLabel,
JLayeredPane,
JMenu,
JMenuBar,
JMenuItem,
JPanel,
JPasswordField,
JPopupMenu,
JProgressBar,
JRadioButton,
JRadioButtonMenuItem,
JScrollBar,
JScrollPane,
JSeparator,
JSlider,
JSplitPane,
JTabbedPane,
JTable,
JTextArea,
JTextCanvas,
JTextField,
JTextPane,
JTextTerm,
JToggleButton,
JToolBar,
JTree,
JWindow,
LineBorder,
MatteBorder,
postEvent,
SoftBevelBorder,
TransferHandler
|
|
