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Eclipse Platform
Release 3.0

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org.eclipse.swt.widgets
Class ScrollBar

java.lang.Object
  org.eclipse.swt.widgets.Widget
      org.eclipse.swt.widgets.ScrollBar

public class ScrollBar

extends Widget

Instances of this class are selectable user interface objects that represent a range of positive, numeric values.

At any given moment, a given scroll bar will have a single selection that is considered to be its value, which is constrained to be within the range of values the scroll bar represents (that is, between its minimum and maximum values).

Typically, scroll bars will be made up of five areas:

1. an arrow button for decrementing the value
2. a page decrement area for decrementing the value by a larger amount
3. a thumb for modifying the value by mouse dragging
4. a page increment area for incrementing the value by a larger amount
5. an arrow button for incrementing the value

Based on their style, scroll bars are either HORIZONTAL (which have a left facing button for decrementing the value and a right facing button for incrementing it) or VERTICAL (which have an upward facing button for decrementing the value and a downward facing buttons for incrementing it).

On some platforms, the size of the scroll bar's thumb can be varied relative to the magnitude of the range of values it represents (that is, relative to the difference between its maximum and minimum values). Typically, this is used to indicate some proportional value such as the ratio of the visible area of a document to the total amount of space that it would take to display it. SWT supports setting the thumb size even if the underlying platform does not, but in this case the appearance of the scroll bar will not change.

Scroll bars are created by specifying either H_SCROLL, V_SCROLL or both when creating a Scrollable. They are accessed from the Scrollable using getHorizontalBar and getVerticalBar.

Note: Scroll bars are not Controls. On some platforms, scroll bars that appear as part of some standard controls such as a text or list have no operating system resources and are not children of the control. For this reason, scroll bars are treated specially. To create a control that looks like a scroll bar but has operating system resources, use Slider.

Styles:

HORIZONTAL, VERTICAL

Events:

Selection

Note: Only one of the styles HORIZONTAL and VERTICAL may be specified.

IMPORTANT: This class is not intended to be subclassed.

See Also:

Slider, Scrollable, Scrollable.getHorizontalBar(), Scrollable.getVerticalBar()

Method Summary

void	addSelectionListener(SelectionListener listener) Adds the listener to the collection of listeners who will be notified when the receiver's value changes, by sending it one of the messages defined in the SelectionListener interface.
void	dispose() Disposes of the operating system resources associated with the receiver and all its descendents.
boolean	getEnabled() Returns true if the receiver is enabled, and false otherwise.
int	getIncrement() Returns the amount that the receiver's value will be modified by when the up/down (or right/left) arrows are pressed.
int	getMaximum() Returns the maximum value which the receiver will allow.
int	getMinimum() Returns the minimum value which the receiver will allow.
int	getPageIncrement() Returns the amount that the receiver's value will be modified by when the page increment/decrement areas are selected.
Scrollable	getParent() Returns the receiver's parent, which must be scrollable.
int	getSelection() Returns the single selection that is the receiver's value.
Point	getSize() Returns a point describing the receiver's size.
int	getThumb() Answers the size of the receiver's thumb relative to the difference between its maximum and minimum values.
boolean	getVisible() Returns true if the receiver is visible, and false otherwise.
boolean	isEnabled() Returns true if the receiver is enabled and all of the receiver's ancestors are enabled, and false otherwise.
boolean	isVisible() Returns true if the receiver is visible and all of the receiver's ancestors are visible and false otherwise.
void	removeSelectionListener(SelectionListener listener) Removes the listener from the collection of listeners who will be notified when the receiver's value changes.
void	setEnabled(boolean enabled) Enables the receiver if the argument is true, and disables it otherwise.
void	setIncrement(int value) Sets the amount that the receiver's value will be modified by when the up/down (or right/left) arrows are pressed to the argument, which must be at least one.
void	setMaximum(int value) Sets the maximum.
void	setMinimum(int value) Sets the minimum value.
void	setPageIncrement(int value) Sets the amount that the receiver's value will be modified by when the page increment/decrement areas are selected to the argument, which must be at least one.
void	setSelection(int selection) Sets the single selection that is the receiver's value to the argument which must be greater than or equal to zero.
void	setThumb(int value) Sets the size of the receiver's thumb relative to the difference between its maximum and minimum values.
void	setValues(int selection, int minimum, int maximum, int thumb, int increment, int pageIncrement) Sets the receiver's selection, minimum value, maximum value, thumb, increment and page increment all at once.
void	setVisible(boolean visible) Marks the receiver as visible if the argument is true, and marks it invisible otherwise.

Methods inherited from class org.eclipse.swt.widgets.Widget

addDisposeListener, addListener, checkSubclass, checkWidget, getData, getData, getDisplay, getStyle, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, removeListener, setData, setData, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

addSelectionListener

public void addSelectionListener(SelectionListener listener)

Adds the listener to the collection of listeners who will be notified when the receiver's value changes, by sending it one of the messages defined in the SelectionListener interface.

When widgetSelected is called, the event object detail field contains one of the following values: 0 - for the end of a drag. SWT.DRAG. SWT.HOME. SWT.END. SWT.ARROW_DOWN. SWT.ARROW_UP. SWT.PAGE_DOWN. SWT.PAGE_UP. widgetDefaultSelected is not called.

Parameters:

listener - the listener which should be notified

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

SelectionListener, removeSelectionListener(org.eclipse.swt.events.SelectionListener), SelectionEvent

dispose

public void dispose()

Description copied from class: Widget

Disposes of the operating system resources associated with the receiver and all its descendents. After this method has been invoked, the receiver and all descendents will answer true when sent the message isDisposed(). Any internal connections between the widgets in the tree will have been removed to facilitate garbage collection.

NOTE: This method is not called recursively on the descendents of the receiver. This means that, widget implementers can not detect when a widget is being disposed of by re-implementing this method, but should instead listen for the Dispose event.

Overrides:

dispose in class Widget

See Also:

Widget.addDisposeListener(org.eclipse.swt.events.DisposeListener), Widget.removeDisposeListener(org.eclipse.swt.events.DisposeListener), Widget.checkWidget()

getEnabled

public boolean getEnabled()

Returns true if the receiver is enabled, and false otherwise. A disabled control is typically not selectable from the user interface and draws with an inactive or "grayed" look.

Returns:

the receiver's enabled state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

isEnabled()

getIncrement

public int getIncrement()

Returns the amount that the receiver's value will be modified by when the up/down (or right/left) arrows are pressed.

Returns:

the increment

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getMaximum

public int getMaximum()

Returns the maximum value which the receiver will allow.

Returns:

the maximum

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getMinimum

public int getMinimum()

Returns the minimum value which the receiver will allow.

Returns:

the minimum

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getPageIncrement

public int getPageIncrement()

Returns the amount that the receiver's value will be modified by when the page increment/decrement areas are selected.

Returns:

the page increment

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getParent

public Scrollable getParent()

Returns the receiver's parent, which must be scrollable.

Returns:

the receiver's parent

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getSelection

public int getSelection()

Returns the single selection that is the receiver's value.

Returns:

the selection

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getSize

public Point getSize()

Returns a point describing the receiver's size. The x coordinate of the result is the width of the receiver. The y coordinate of the result is the height of the receiver.

Returns:

the receiver's size

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

getThumb

public int getThumb()

Answers the size of the receiver's thumb relative to the difference between its maximum and minimum values.

Returns:

the thumb value

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

ScrollBar

getVisible

public boolean getVisible()

Returns true if the receiver is visible, and false otherwise.

If one of the receiver's ancestors is not visible or some other condition makes the receiver not visible, this method may still indicate that it is considered visible even though it may not actually be showing.

Returns:

the receiver's visibility state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

isEnabled

public boolean isEnabled()

Returns true if the receiver is enabled and all of the receiver's ancestors are enabled, and false otherwise. A disabled control is typically not selectable from the user interface and draws with an inactive or "grayed" look.

Returns:

the receiver's enabled state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

getEnabled()

isVisible

public boolean isVisible()

Returns true if the receiver is visible and all of the receiver's ancestors are visible and false otherwise.

Returns:

the receiver's visibility state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

getVisible()

removeSelectionListener

public void removeSelectionListener(SelectionListener listener)

Removes the listener from the collection of listeners who will be notified when the receiver's value changes.

Parameters:

listener - the listener which should no longer be notified

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

SelectionListener, addSelectionListener(org.eclipse.swt.events.SelectionListener)

setEnabled

public void setEnabled(boolean enabled)

Enables the receiver if the argument is true, and disables it otherwise. A disabled control is typically not selectable from the user interface and draws with an inactive or "grayed" look.

Parameters:

enabled - the new enabled state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setIncrement

public void setIncrement(int value)

Sets the amount that the receiver's value will be modified by when the up/down (or right/left) arrows are pressed to the argument, which must be at least one.

Parameters:

value - the new increment (must be greater than zero)

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setMaximum

public void setMaximum(int value)

Sets the maximum. If this value is negative or less than or equal to the minimum, the value is ignored. If necessary, first the thumb and then the selection are adjusted to fit within the new range.

Parameters:

value - the new maximum

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setMinimum

public void setMinimum(int value)

Sets the minimum value. If this value is negative or greater than or equal to the maximum, the value is ignored. If necessary, first the thumb and then the selection are adjusted to fit within the new range.

Parameters:

value - the new minimum

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setPageIncrement

public void setPageIncrement(int value)

Sets the amount that the receiver's value will be modified by when the page increment/decrement areas are selected to the argument, which must be at least one.

Parameters:

value - the page increment (must be greater than zero)

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setSelection

public void setSelection(int selection)

Sets the single selection that is the receiver's value to the argument which must be greater than or equal to zero.

Parameters:

selection - the new selection (must be zero or greater)

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setThumb

public void setThumb(int value)

Sets the size of the receiver's thumb relative to the difference between its maximum and minimum values. This new value will be ignored if it is less than one, and will be clamped if it exceeds the receiver's current range.

Parameters:

value - the new thumb value, which must be at least one and not larger than the size of the current range

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setValues

public void setValues(int selection,
                      int minimum,
                      int maximum,
                      int thumb,
                      int increment,
                      int pageIncrement)

Sets the receiver's selection, minimum value, maximum value, thumb, increment and page increment all at once.

Note: This is equivalent to setting the values individually using the appropriate methods, but may be implemented in a more efficient fashion on some platforms.

Parameters:

selection - the new selection value

minimum - the new minimum value

maximum - the new maximum value

thumb - the new thumb value

increment - the new increment value

pageIncrement - the new pageIncrement value

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setVisible

public void setVisible(boolean visible)

Marks the receiver as visible if the argument is true, and marks it invisible otherwise.

If one of the receiver's ancestors is not visible or some other condition makes the receiver not visible, marking it visible may not actually cause it to be displayed.

Parameters:

visible - the new visibility state

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver