Eclipse Platform
Release 3.7

org.eclipse.swt.widgets
Class Button

java.lang.Object
  extended by org.eclipse.swt.widgets.Widget
      extended by org.eclipse.swt.widgets.Control
          extended by org.eclipse.swt.widgets.Button
All Implemented Interfaces:
Drawable

public class Button
extends Control

Instances of this class represent a selectable user interface object that issues notification when pressed and released.

Styles:
ARROW, CHECK, PUSH, RADIO, TOGGLE, FLAT
UP, DOWN, LEFT, RIGHT, CENTER
Events:
Selection

Note: Only one of the styles ARROW, CHECK, PUSH, RADIO, and TOGGLE may be specified.

Note: Only one of the styles LEFT, RIGHT, and CENTER may be specified.

Note: Only one of the styles UP, DOWN, LEFT, and RIGHT may be specified when the ARROW style is specified.

IMPORTANT: This class is not intended to be subclassed.

See Also:
Button snippets, SWT Example: ControlExample, Sample code and further information
Restriction:
This class is not intended to be subclassed by clients.

Field Summary
 
Fields inherited from class org.eclipse.swt.widgets.Control
handle
 
Constructor Summary
Button(Composite 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 control is selected by the user, by sending it one of the messages defined in the SelectionListener interface.
 Point computeSize(int wHint, int hHint, boolean changed)
          Returns the preferred size of the receiver.
 int getAlignment()
          Returns a value which describes the position of the text or image in the receiver.
 boolean getGrayed()
          Returns true if the receiver is grayed, and false otherwise.
 Image getImage()
          Returns the receiver's image if it has one, or null if it does not.
 boolean getSelection()
          Returns true if the receiver is selected, and false otherwise.
 String getText()
          Returns the receiver's text, which will be an empty string if it has never been set or if the receiver is an ARROW button.
 void removeSelectionListener(SelectionListener listener)
          Removes the listener from the collection of listeners who will be notified when the control is selected by the user.
 void setAlignment(int alignment)
          Controls how text, images and arrows will be displayed in the receiver.
 boolean setFocus()
          Causes the receiver to have the keyboard focus, such that all keyboard events will be delivered to it.
 void setGrayed(boolean grayed)
          Sets the grayed state of the receiver.
 void setImage(Image image)
          Sets the receiver's image to the argument, which may be null indicating that no image should be displayed.
 void setSelection(boolean selected)
          Sets the selection state of the receiver, if it is of type CHECK, RADIO, or TOGGLE.
 void setText(String string)
          Sets the receiver's text.
 
Methods inherited from class org.eclipse.swt.widgets.Control
addControlListener, addDragDetectListener, addFocusListener, addGestureListener, addHelpListener, addKeyListener, addMenuDetectListener, addMouseListener, addMouseMoveListener, addMouseTrackListener, addMouseWheelListener, addPaintListener, addTouchListener, addTraverseListener, computeSize, dragDetect, dragDetect, forceFocus, getAccessible, getBackground, getBackgroundImage, getBorderWidth, getBounds, getCursor, getDragDetect, getEnabled, getFont, getForeground, getLayoutData, getLocation, getMenu, getMonitor, getOrientation, getParent, getRegion, getShell, getSize, getToolTipText, getTouchEnabled, getVisible, internal_dispose_GC, internal_new_GC, isEnabled, isFocusControl, isReparentable, isVisible, moveAbove, moveBelow, pack, pack, print, redraw, redraw, removeControlListener, removeDragDetectListener, removeFocusListener, removeGestureListener, removeHelpListener, removeKeyListener, removeMenuDetectListener, removeMouseListener, removeMouseMoveListener, removeMouseTrackListener, removeMouseWheelListener, removePaintListener, removeTouchListener, removeTraverseListener, setBackground, setBackgroundImage, setBounds, setBounds, setCapture, setCursor, setDragDetect, setEnabled, setFont, setForeground, setLayoutData, setLocation, setLocation, setMenu, setOrientation, setParent, setRedraw, setRegion, setSize, setSize, setToolTipText, setTouchEnabled, setVisible, toControl, toControl, toDisplay, toDisplay, traverse, traverse, traverse, update
 
Methods inherited from class org.eclipse.swt.widgets.Widget
addDisposeListener, addListener, checkSubclass, checkWidget, dispose, getData, getData, getDisplay, getListeners, getStyle, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, removeListener, reskin, setData, setData, toString
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Button

public Button(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:
SWT.ARROW, SWT.CHECK, SWT.PUSH, SWT.RADIO, SWT.TOGGLE, SWT.FLAT, SWT.UP, SWT.DOWN, SWT.LEFT, SWT.RIGHT, SWT.CENTER, Widget.checkSubclass(), Widget.getStyle()
Method Detail

addSelectionListener

public void addSelectionListener(SelectionListener listener)
Adds the listener to the collection of listeners who will be notified when the control is selected by the user, by sending it one of the messages defined in the SelectionListener interface.

widgetSelected is called when the control is selected by the user. widgetDefaultSelected is not called.

When the SWT.RADIO style bit is set, the widgetSelected method is also called when the receiver loses selection because another item in the same radio group was selected by the user. During widgetSelected the application can use getSelection() to determine the current selected state of the receiver.

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

computeSize

public Point computeSize(int wHint,
                         int hHint,
                         boolean changed)
Description copied from class: Control
Returns the preferred size of the receiver.

The preferred size of a control is the size that it would best be displayed at. The width hint and height hint arguments allow the caller to ask a control questions such as "Given a particular width, how high does the control need to be to show all of the contents?" To indicate that the caller does not wish to constrain a particular dimension, the constant SWT.DEFAULT is passed for the hint.

If the changed flag is true, it indicates that the receiver's contents have changed, therefore any caches that a layout manager containing the control may have been keeping need to be flushed. When the control is resized, the changed flag will be false, so layout manager caches can be retained.

Overrides:
computeSize in class Control
Parameters:
wHint - the width hint (can be SWT.DEFAULT)
hHint - the height hint (can be SWT.DEFAULT)
changed - true if the control's contents have changed, and false otherwise
Returns:
the preferred size of the control.
See Also:
Layout, Control.getBorderWidth(), Control.getBounds(), Control.getSize(), Control.pack(boolean), "computeTrim, getClientArea for controls that implement them"

getAlignment

public int getAlignment()
Returns a value which describes the position of the text or image in the receiver. The value will be one of LEFT, RIGHT or CENTER unless the receiver is an ARROW button, in which case, the alignment will indicate the direction of the arrow (one of LEFT, RIGHT, UP or DOWN).

Returns:
the alignment
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

getGrayed

public boolean getGrayed()
Returns true if the receiver is grayed, and false otherwise. When the widget does not have the CHECK style, return false.

Returns:
the grayed state of the checkbox
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

getImage

public Image getImage()
Returns the receiver's image if it has one, or null if it does not.

Returns:
the receiver's image
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 boolean getSelection()
Returns true if the receiver is selected, and false otherwise.

When the receiver is of type CHECK or RADIO, it is selected when it is checked. When it is of type TOGGLE, it is selected when it is pushed in. If the receiver is of any other type, this method returns false.

Returns:
the selection 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

getText

public String getText()
Returns the receiver's text, which will be an empty string if it has never been set or if the receiver is an ARROW button.

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

removeSelectionListener

public void removeSelectionListener(SelectionListener listener)
Removes the listener from the collection of listeners who will be notified when the control is selected by the user.

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)

setAlignment

public void setAlignment(int alignment)
Controls how text, images and arrows will be displayed in the receiver. The argument should be one of LEFT, RIGHT or CENTER unless the receiver is an ARROW button, in which case, the argument indicates the direction of the arrow (one of LEFT, RIGHT, UP or DOWN).

Parameters:
alignment - the new alignment
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

setFocus

public boolean setFocus()
Description copied from class: Control
Causes the receiver to have the keyboard focus, such that all keyboard events will be delivered to it. Focus reassignment will respect applicable platform constraints.

Overrides:
setFocus in class Control
Returns:
true if the control got focus, and false if it was unable to.
See Also:
Control.forceFocus()

setImage

public void setImage(Image image)
Sets the receiver's image to the argument, which may be null indicating that no image should be displayed.

Note that a Button can display an image and text simultaneously on Windows (starting with XP), GTK+ and OSX. On other platforms, a Button that has an image and text set into it will display the image or text that was set most recently.

Parameters:
image - the image to display on the receiver (may be null)
Throws:
IllegalArgumentException -
  • ERROR_INVALID_ARGUMENT - if the image has been disposed
SWTException -
  • ERROR_WIDGET_DISPOSED - if the receiver has been disposed
  • ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

setGrayed

public void setGrayed(boolean grayed)
Sets the grayed state of the receiver. This state change only applies if the control was created with the SWT.CHECK style.

Parameters:
grayed - the new grayed 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

setSelection

public void setSelection(boolean selected)
Sets the selection state of the receiver, if it is of type CHECK, RADIO, or TOGGLE.

When the receiver is of type CHECK or RADIO, it is selected when it is checked. When it is of type TOGGLE, it is selected when it is pushed in.

Parameters:
selected - the new selection 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

setText

public void setText(String string)
Sets the receiver's text.

This method sets the button label. The label may include the mnemonic character but must not contain line delimiters.

Mnemonics are indicated by an '&' that causes the next character to be the mnemonic. When the user presses a key sequence that matches the mnemonic, a selection event occurs. On most platforms, the mnemonic appears underlined but may be emphasized in a platform specific manner. The mnemonic indicator character '&' can be escaped by doubling it in the string, causing a single '&' to be displayed.

Note that a Button can display an image and text simultaneously on Windows (starting with XP), GTK+ and OSX. On other platforms, a Button that has an image and text set into it will display the image or text that was set most recently.

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

Eclipse Platform
Release 3.7

Guidelines for using Eclipse APIs.

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