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Release 3.0

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org.eclipse.swt.widgets
Class Widget

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

Direct Known Subclasses:

Caret, Control, DragSource, DropTarget, Item, Menu, ScrollBar, Tracker, Tray

public abstract class Widget

extends Object

This class is the abstract superclass of all user interface objects. Widgets are created, disposed and issue notification to listeners when events occur which affect them.

Styles:

(none)

Events:

Dispose

IMPORTANT: This class is intended to be subclassed only within the SWT implementation. However, it has not been marked final to allow those outside of the SWT development team to implement patched versions of the class in order to get around specific limitations in advance of when those limitations can be addressed by the team. Any class built using subclassing to access the internals of this class will likely fail to compile or run between releases and may be strongly platform specific. Subclassing should not be attempted without an intimate and detailed understanding of the workings of the hierarchy. No support is provided for user-written classes which are implemented as subclasses of this class.

See Also:

checkSubclass()

Constructor Summary

Widget(Widget 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	addDisposeListener(DisposeListener listener) Adds the listener to the collection of listeners who will be notifed when the widget is disposed.
void	addListener(int eventType, Listener listener) Adds the listener to the collection of listeners who will be notifed when an event of the given type occurs.
protected void	checkSubclass() Checks that this class can be subclassed.
protected void	checkWidget() Throws an SWTException if the receiver can not be accessed by the caller.
void	dispose() Disposes of the operating system resources associated with the receiver and all its descendents.
Object	getData() Returns the application defined widget data associated with the receiver, or null if it has not been set.
Object	getData(String key) Returns the application defined property of the receiver with the specified name, or null if it has not been set.
Display	getDisplay() Returns the Display that is associated with the receiver.
int	getStyle() Returns the receiver's style information.
boolean	isDisposed() Returns true if the widget has been disposed, and false otherwise.
protected boolean	isListening(int eventType) Returns true if there are any listeners for the specified event type associated with the receiver, and false otherwise.
void	notifyListeners(int eventType, Event event) Notifies all of the receiver's listeners for events of the given type that one such event has occurred by invoking their handleEvent() method.
void	removeDisposeListener(DisposeListener listener) Removes the listener from the collection of listeners who will be notifed when the widget is disposed.
void	removeListener(int eventType, Listener listener) Removes the listener from the collection of listeners who will be notifed when an event of the given type occurs.
protected void	removeListener(int eventType, org.eclipse.swt.internal.SWTEventListener listener) Removes the listener from the collection of listeners who will be notifed when an event of the given type occurs.
void	setData(Object data) Sets the application defined widget data associated with the receiver to be the argument.
void	setData(String key, Object value) Sets the application defined property of the receiver with the specified name to the given value.
String	toString() Returns a string containing a concise, human-readable description of the receiver.

Methods inherited from class java.lang.Object

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

Constructor Detail

Widget

public Widget(Widget 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 widget which will be the parent of the new instance (cannot be null)

style - the style of widget 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, checkSubclass(), getStyle()

Method Detail

addListener

public void addListener(int eventType,
                        Listener listener)

Adds the listener to the collection of listeners who will be notifed when an event of the given type occurs. When the event does occur in the widget, the listener is notified by sending it the handleEvent() message.

Parameters:

eventType - the type of event to listen for

listener - the listener which should be notified when the event occurs

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:

Listener, removeListener(int, org.eclipse.swt.widgets.Listener)

addDisposeListener

public void addDisposeListener(DisposeListener listener)

Adds the listener to the collection of listeners who will be notifed when the widget is disposed. When the widget is disposed, the listener is notified by sending it the widgetDisposed() message.

Parameters:

listener - the listener which should be notified when the receiver is disposed

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:

DisposeListener, removeDisposeListener(org.eclipse.swt.events.DisposeListener)

checkSubclass

protected void checkSubclass()

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.

Throws:

SWTException -

• ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass

checkWidget

protected void checkWidget()

Throws an SWTException if the receiver can not be accessed by the caller. This may include both checks on the state of the receiver and more generally on the entire execution context. This method should be called by widget implementors to enforce the standard SWT invariants.

Currently, it is an error to invoke any method (other than isDisposed()) on a widget that has had its dispose() method called. It is also an error to call widget methods from any thread that is different from the thread that created the widget.

In future releases of SWT, there may be more or fewer error checks and exceptions may be thrown for different reasons.

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

dispose

public void dispose()

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.

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

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

getData

public Object getData()

Returns the application defined widget data associated with the receiver, or null if it has not been set. The widget data is a single, unnamed field that is stored with every widget.

Applications may put arbitrary objects in this field. If the object stored in the widget data needs to be notified when the widget is disposed of, it is the application's responsibility to hook the Dispose event on the widget and do so.

Returns:

the widget data

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - when the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - when called from the wrong thread

See Also:

setData(java.lang.Object)

getData

public Object getData(String key)

Returns the application defined property of the receiver with the specified name, or null if it has not been set.

Applications may have associated arbitrary objects with the receiver in this fashion. If the objects stored in the properties need to be notified when the widget is disposed of, it is the application's responsibility to hook the Dispose event on the widget and do so.

Parameters:

key - the name of the property

Returns:

the value of the property or null if it has not been set

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the key 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:

setData(java.lang.Object)

getDisplay

public Display getDisplay()

Returns the Display that is associated with the receiver.

A widget's display is either provided when it is created (for example, top level Shells) or is the same as its parent's display.

Returns:

the receiver's display

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

getStyle

public int getStyle()

Returns the receiver's style information.

Note that the value which is returned by this method may not match the value which was provided to the constructor when the receiver was created. This can occur when the underlying operating system does not support a particular combination of requested styles. For example, if the platform widget used to implement a particular SWT widget always has scroll bars, the result of calling this method would always have the SWT.H_SCROLL and SWT.V_SCROLL bits set.

Returns:

the style bits

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

isDisposed

public boolean isDisposed()

Returns true if the widget has been disposed, and false otherwise.

This method gets the dispose state for the widget. When a widget has been disposed, it is an error to invoke any other method using the widget.

Returns:

true when the widget is disposed and false otherwise

isListening

protected boolean isListening(int eventType)

Returns true if there are any listeners for the specified event type associated with the receiver, and false otherwise.

Parameters:

eventType - the type of event

Returns:

true if the event is hooked

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

notifyListeners

public void notifyListeners(int eventType,
                            Event event)

Notifies all of the receiver's listeners for events of the given type that one such event has occurred by invoking their handleEvent() method.

Parameters:

eventType - the type of event which has occurred

event - the event data

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

removeListener

public void removeListener(int eventType,
                           Listener listener)

Removes the listener from the collection of listeners who will be notifed when an event of the given type occurs.

Parameters:

eventType - the type of event to listen for

listener - the listener which should no longer be notified when the event occurs

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:

Listener, addListener(int, org.eclipse.swt.widgets.Listener)

removeListener

protected void removeListener(int eventType,
                              org.eclipse.swt.internal.SWTEventListener listener)

Removes the listener from the collection of listeners who will be notifed when an event of the given type occurs.

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

Parameters:

eventType - the type of event to listen for

listener - the listener which should no longer be notified when the event occurs

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:

Listener, addListener(int, org.eclipse.swt.widgets.Listener)

removeDisposeListener

public void removeDisposeListener(DisposeListener listener)

Removes the listener from the collection of listeners who will be notifed when the widget is disposed.

Parameters:

listener - the listener which should no longer be notified when the receiver is disposed

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:

DisposeListener, addDisposeListener(org.eclipse.swt.events.DisposeListener)

setData

public void setData(Object data)

Sets the application defined widget data associated with the receiver to be the argument. The widget data is a single, unnamed field that is stored with every widget.

Applications may put arbitrary objects in this field. If the object stored in the widget data needs to be notified when the widget is disposed of, it is the application's responsibility to hook the Dispose event on the widget and do so.

Parameters:

data - the widget data

Throws:

SWTException -

• ERROR_WIDGET_DISPOSED - when the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - when called from the wrong thread

setData

public void setData(String key,
                    Object value)

Sets the application defined property of the receiver with the specified name to the given value.

Applications may associate arbitrary objects with the receiver in this fashion. If the objects stored in the properties need to be notified when the widget is disposed of, it is the application's responsibility to hook the Dispose event on the widget and do so.

Parameters:

key - the name of the property

value - the new value for the property

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the key 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:

getData()

toString

public String toString()

Returns a string containing a concise, human-readable description of the receiver.

Returns:

a string representation of the receiver