org.eclipse.swt.widgets
Class ScrollBar

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

All Implemented Interfaces:

Adaptable

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.

Since:

1.0

See Also:

(current) limitations:

• minimum, maximum, thumb, increment and pageIncrement properties are not rendered (no corresponding client-side property)

Constructor Summary

ScrollBar(Scrollable parent, int style)
Constructs a new instance of this class given its parent and a style value describing its behavior and appearance.

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.
boolean	getEnabled() Returns true if the receiver is enabled, and false otherwise.
int	getMaximum() Returns the maximum value which the receiver will allow.
int	getMinimum() Returns the minimum value which the receiver will allow.
Scrollable	getParent() Returns the receiver's parent, which must be a 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() Returns 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	setMaximum(int maximum) Sets the maximum.
void	setMinimum(int minimum) Sets the minimum value.
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 thumb) Sets the size of the receiver's thumb relative to the difference between its maximum and minimum values.
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, dispose, getAdapter, getData, getData, getDisplay, getListeners, getStyle, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, reskin, setData, setData, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

ScrollBar

public ScrollBar(Scrollable parent,
                 int style)

Constructs a new instance of this class given its parent and a style value describing its behavior and appearance.

The style value is either one of the style constants defined in class SWT which is applicable to instances of this class, or must be built by bitwise OR'ing together (that is, using the int "|" operator) two or more of those SWT style constants. The class description lists the style constants that are applicable to the class. Style bits are also inherited from superclasses.

Parameters:

parent - a composite control which will be the parent of the new instance (cannot be null)

style - the style of control to construct

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the parent is null

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent
• ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass

IMPORTANT: This method is not part of the RWT public API. It is marked public only so that it can be shared within the packages provided by RWT. It should never be accessed from application code.

See Also:

SWT.HORIZONTAL, SWT.VERTICAL, Widget.checkSubclass(), Widget.getStyle()

Method Detail

getParent

public Scrollable getParent()

Returns the receiver's parent, which must be a 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

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

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

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()

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

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()

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()

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()

Returns 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

setThumb

public void setThumb(int thumb)

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:

thumb - 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

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

setMaximum

public void setMaximum(int maximum)

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:

maximum - 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

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

setMinimum

public void setMinimum(int minimum)

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:

minimum - 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

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

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

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: SWT.NONE - 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

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)