Class Combo

All Implemented Interfaces:
Drawable

public class Combo extends Composite
Instances of this class are controls that allow the user to choose an item from a list of items, or optionally enter a new value by typing it into an editable text field. Often, Combos are used in the same place where a single selection List widget could be used but space is limited. A Combo takes less space than a List widget and shows similar information.

Note: Since Combos can contain both a list and an editable text field, it is possible to confuse methods which access one versus the other (compare for example, clearSelection() and deselectAll()). The API documentation is careful to indicate either "the receiver's list" or the "the receiver's text field" to distinguish between the two cases.

Note that although this class is a subclass of Composite, it does not make sense to add children to it, or set a layout on it.

Styles:
DROP_DOWN, READ_ONLY, SIMPLE
Events:
DefaultSelection, Modify, Selection, Verify, OrientationChange

Note: Only one of the styles DROP_DOWN and SIMPLE may be specified.

IMPORTANT: This class is not intended to be subclassed.

See Also:
Restriction:
This class is not intended to be subclassed by clients.
  • Field Details

    • LIMIT

      public static final int LIMIT
      the operating system limit for the number of characters that the text field in an instance of this class can hold
  • Constructor Details

    • Combo

      public Combo(Composite 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
      See Also:
  • Method Details

    • add

      public void add(String string)
      Adds the argument to the end of the receiver's list.

      Note: If control characters like '\n', '\t' etc. are used in the string, then the behavior is platform dependent.

      Parameters:
      string - the new item
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string 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:
    • add

      public void add(String string, int index)
      Adds the argument to the receiver's list at the given zero-relative index.

      Note: To add an item at the end of the list, use the result of calling getItemCount() as the index or use add(String).

      Also note, if control characters like '\n', '\t' etc. are used in the string, then the behavior is platform dependent.

      Parameters:
      string - the new item
      index - the index for the item
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string is null
      • ERROR_INVALID_RANGE - if the index is not between 0 and the number of elements in the list (inclusive)
      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:
    • addModifyListener

      public void addModifyListener(ModifyListener listener)
      Adds the listener to the collection of listeners who will be notified when the receiver's text is modified, by sending it one of the messages defined in the ModifyListener interface.
      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:
    • addSegmentListener

      public void addSegmentListener(SegmentListener listener)
      Adds a segment listener.

      A SegmentEvent is sent whenever text content is being modified or a segment listener is added or removed. You can customize the appearance of text by indicating certain characters to be inserted at certain text offsets. This may be used for bidi purposes, e.g. when adjacent segments of right-to-left text should not be reordered relative to each other. E.g., multiple Java string literals in a right-to-left language should generally remain in logical order to each other, that is, the way they are stored.

      Warning: This API is currently only implemented on Windows. SegmentEvents won't be sent on GTK and Cocoa.

      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
      Since:
      3.103
      See Also:
    • addSelectionListener

      public void addSelectionListener(SelectionListener listener)
      Adds the listener to the collection of listeners who will be notified when the user changes the receiver's selection, by sending it one of the messages defined in the SelectionListener interface.

      widgetSelected is called when the user changes the combo's list selection. widgetDefaultSelected is typically called when ENTER is pressed the combo's text area.

      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:
    • addVerifyListener

      public void addVerifyListener(VerifyListener listener)
      Adds the listener to the collection of listeners who will be notified when the receiver's text is verified, by sending it one of the messages defined in the VerifyListener interface.
      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
      Since:
      3.1
      See Also:
    • checkSubclass

      protected void checkSubclass()
      Description copied from class: Widget
      Checks that this class can be subclassed.

      The SWT class library is intended to be subclassed only at specific, controlled points (most notably, Composite and Canvas when implementing new widgets). This method enforces this rule unless it is overridden.

      IMPORTANT: By providing an implementation of this method that allows a subclass of a class which does not normally allow subclassing to be created, the implementer agrees to be fully responsible for the fact that any such subclass will likely fail between SWT releases and will be strongly platform specific. No support is provided for user-written classes which are implemented in this fashion.

      The ability to subclass outside of the allowed SWT classes is intended purely to enable those not on the SWT development team to implement patches in order to get around specific limitations in advance of when those limitations can be addressed by the team. Subclassing should not be attempted without an intimate and detailed understanding of the hierarchy.

      Overrides:
      checkSubclass in class Composite
    • clearSelection

      public void clearSelection()
      Sets the selection in the receiver's text field to an empty selection starting just before the first character. If the text field is editable, this has the effect of placing the i-beam at the start of the text.

      Note: To clear the selected items in the receiver's list, use deselectAll().

      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:
    • copy

      public void copy()
      Copies the selected text.

      The current selection is copied to the clipboard.

      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
      Since:
      2.1
    • cut

      public void cut()
      Cuts the selected text.

      The current selection is first copied to the clipboard and then deleted from the widget.

      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
      Since:
      2.1
    • deselect

      public void deselect(int index)
      Deselects the item at the given zero-relative index in the receiver's list. If the item at the index was already deselected, it remains deselected. Indices that are out of range are ignored.
      Parameters:
      index - the index of the item to deselect
      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
    • deselectAll

      public void deselectAll()
      Deselects all selected items in the receiver's list.

      Note: To clear the selection in the receiver's text field, use clearSelection().

      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:
    • getCaretLocation

      public Point getCaretLocation()
      Returns a point describing the location of the caret relative to the receiver.
      Returns:
      a point, the location of the caret
      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
      Since:
      3.8
    • getCaretPosition

      public int getCaretPosition()
      Returns the character position of the caret.

      Indexing is zero based.

      Returns:
      the position of the caret
      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
      Since:
      3.8
    • getItem

      public String getItem(int index)
      Returns the item at the given, zero-relative index in the receiver's list. Throws an exception if the index is out of range.
      Parameters:
      index - the index of the item to return
      Returns:
      the item at the given index
      Throws:
      IllegalArgumentException -
      • ERROR_INVALID_RANGE - if the index is not between 0 and the number of elements in the list minus 1 (inclusive)
      SWTException -
      • ERROR_WIDGET_DISPOSED - if the receiver has been disposed
      • ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
    • getItemCount

      public int getItemCount()
      Returns the number of items contained in the receiver's list.
      Returns:
      the number of items
      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
    • getItemHeight

      public int getItemHeight()
      Returns the height of the area which would be used to display one of the items in the receiver's list.
      Returns:
      the height of one item
      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
    • getItems

      public String[] getItems()
      Returns a (possibly empty) array of Strings which are the items in the receiver's list.

      Note: This is not the actual structure used by the receiver to maintain its list of items, so modifying the array will not affect the receiver.

      Returns:
      the items in the receiver's list
      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
    • getListVisible

      public boolean getListVisible()
      Returns true if the receiver's list 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 list'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
      Since:
      3.4
    • setListVisible

      public void setListVisible(boolean visible)
      Marks the receiver's list 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
      Since:
      3.4
    • getOrientation

      public int getOrientation()
      Returns the orientation of the receiver.
      Overrides:
      getOrientation in class Control
      Returns:
      the orientation style
      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
      Since:
      2.1.2
    • getSelection

      public Point getSelection()
      Returns a Point whose x coordinate is the character position representing the start of the selection in the receiver's text field, and whose y coordinate is the character position representing the end of the selection. An "empty" selection is indicated by the x and y coordinates having the same value.

      Indexing is zero based. The range of a selection is from 0..N where N is the number of characters in the widget.

      Returns:
      a point representing the selection start and end
      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
    • getSelectionIndex

      public int getSelectionIndex()
      Returns the zero-relative index of the item which is currently selected in the receiver's list, or -1 if no item is selected.
      Returns:
      the index of the selected item
      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
    • getText

      public String getText()
      Returns a string containing a copy of the contents of the receiver's text field, or an empty string if there are no contents.
      Returns:
      the receiver's text
      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
    • getTextHeight

      public int getTextHeight()
      Returns the height of the receivers's text field.
      Returns:
      the text height
      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
    • getTextLimit

      public int getTextLimit()
      Returns the maximum number of characters that the receiver's text field is capable of holding. If this has not been changed by setTextLimit(), it will be the constant Combo.LIMIT.
      Returns:
      the text limit
      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:
    • getVisibleItemCount

      public int getVisibleItemCount()
      Gets the number of items that are visible in the drop down portion of the receiver's list.

      Note: This operation is a hint and is not supported on platforms that do not have this concept.

      Returns:
      the number of items that are visible
      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
      Since:
      3.0
    • indexOf

      public int indexOf(String string)
      Searches the receiver's list starting at the first item (index 0) until an item is found that is equal to the argument, and returns the index of that item. If no item is found, returns -1.
      Parameters:
      string - the search item
      Returns:
      the index of the item
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string 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
    • indexOf

      public int indexOf(String string, int start)
      Searches the receiver's list starting at the given, zero-relative index until an item is found that is equal to the argument, and returns the index of that item. If no item is found or the starting index is out of range, returns -1.
      Parameters:
      string - the search item
      start - the zero-relative index at which to begin the search
      Returns:
      the index of the item
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string 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
    • paste

      public void paste()
      Pastes text from clipboard.

      The selected text is deleted from the widget and new text inserted from the clipboard.

      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
      Since:
      2.1
    • remove

      public void remove(int index)
      Removes the item from the receiver's list at the given zero-relative index.
      Parameters:
      index - the index for the item
      Throws:
      IllegalArgumentException -
      • ERROR_INVALID_RANGE - if the index is not between 0 and the number of elements in the list minus 1 (inclusive)
      SWTException -
      • ERROR_WIDGET_DISPOSED - if the receiver has been disposed
      • ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
    • remove

      public void remove(int start, int end)
      Removes the items from the receiver's list which are between the given zero-relative start and end indices (inclusive).
      Parameters:
      start - the start of the range
      end - the end of the range
      Throws:
      IllegalArgumentException -
      • ERROR_INVALID_RANGE - if either the start or end are not between 0 and the number of elements in the list minus 1 (inclusive)
      SWTException -
      • ERROR_WIDGET_DISPOSED - if the receiver has been disposed
      • ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
    • remove

      public void remove(String string)
      Searches the receiver's list starting at the first item until an item is found that is equal to the argument, and removes that item from the list.
      Parameters:
      string - the item to remove
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string is null
      • ERROR_INVALID_ARGUMENT - if the string is not found in the list
      SWTException -
      • ERROR_WIDGET_DISPOSED - if the receiver has been disposed
      • ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
    • removeAll

      public void removeAll()
      Removes all of the items from the receiver's list and clear the contents of receiver's text field.
      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
    • removeModifyListener

      public void removeModifyListener(ModifyListener listener)
      Removes the listener from the collection of listeners who will be notified when the receiver's text is modified.
      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:
    • removeSegmentListener

      public void removeSegmentListener(SegmentListener listener)
      Removes the listener from the collection of listeners who will be notified when the receiver's text is modified.
      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
      Since:
      3.103
      See Also:
    • removeSelectionListener

      public void removeSelectionListener(SelectionListener listener)
      Removes the listener from the collection of listeners who will be notified when the user changes the receiver's selection.
      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:
    • removeVerifyListener

      public void removeVerifyListener(VerifyListener listener)
      Removes the listener from the collection of listeners who will be notified when the control is verified.
      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
      Since:
      3.1
      See Also:
    • select

      public void select(int index)
      Selects the item at the given zero-relative index in the receiver's list. If the item at the index was already selected, it remains selected. Indices that are out of range are ignored.
      Parameters:
      index - the index of the item to select
      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
    • setFont

      public void setFont(Font font)
      Description copied from class: Control
      Sets the font that the receiver will use to paint textual information to the font specified by the argument, or to the default font for that kind of control if the argument is null.
      Overrides:
      setFont in class Control
      Parameters:
      font - the new font (or null)
    • setItem

      public void setItem(int index, String string)
      Sets the text of the item in the receiver's list at the given zero-relative index to the string argument.
      Parameters:
      index - the index for the item
      string - the new text for the item
      Throws:
      IllegalArgumentException -
      • ERROR_INVALID_RANGE - if the index is not between 0 and the number of elements in the list minus 1 (inclusive)
      • ERROR_NULL_ARGUMENT - if the string 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
    • setItems

      public void setItems(String... items)
      Sets the receiver's list to be the given array of items.
      Parameters:
      items - the array of items
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the items array is null
      • ERROR_INVALID_ARGUMENT - if an item in the items array 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
    • setOrientation

      public void setOrientation(int orientation)
      Sets the orientation of the receiver, which must be one of the constants SWT.LEFT_TO_RIGHT or SWT.RIGHT_TO_LEFT.
      Overrides:
      setOrientation in class Control
      Parameters:
      orientation - new orientation style
      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
      Since:
      2.1.2
    • setSelection

      public void setSelection(Point selection)
      Sets the selection in the receiver's text field to the range specified by the argument whose x coordinate is the start of the selection and whose y coordinate is the end of the selection.
      Parameters:
      selection - a point representing the new selection start and end
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the point 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
    • setText

      public void setText(String string)
      Sets the contents of the receiver's text field to the given string.

      This call is ignored when the receiver is read only and the given string is not in the receiver's list.

      Note: The text field in a Combo is typically only capable of displaying a single line of text. Thus, setting the text to a string containing line breaks or other special characters will probably cause it to display incorrectly.

      Also note, if control characters like '\n', '\t' etc. are used in the string, then the behavior is platform dependent.

      Parameters:
      string - the new text
      Throws:
      IllegalArgumentException -
      • ERROR_NULL_ARGUMENT - if the string 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
    • setTextLimit

      public void setTextLimit(int limit)
      Sets the maximum number of characters that the receiver's text field is capable of holding to be the argument.

      To reset this value to the default, use setTextLimit(Combo.LIMIT). Specifying a limit value larger than Combo.LIMIT sets the receiver's limit to Combo.LIMIT.

      Parameters:
      limit - new text limit
      Throws:
      IllegalArgumentException -
      • ERROR_CANNOT_BE_ZERO - if the limit is zero
      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:
    • setVisibleItemCount

      public void setVisibleItemCount(int count)
      Sets the number of items that are visible in the drop down portion of the receiver's list.

      Note: This operation is a hint and is not supported on platforms that do not have this concept.

      Parameters:
      count - the new number of items to be visible
      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
      Since:
      3.0