Eclipse Community Forums: Eclipse Platform » Why is it needed for java bean to implement property change support

Help

Home

Home » Eclipse Projects » Eclipse Platform » Why is it needed for java bean to implement property change support

Show: Today's Messages :: Show Polls :: Message Navigator

Why is it needed for java bean to implement property change support [message #328349]

Thu, 22 May 2008 15:49

Hao Missing name

Messages: 115
Registered: July 2009

Senior Member

jface databinding framwork has provided a lot of help classes, such as
BeansObservables and WritableValue. Why is it still needed for java bean
to implement property change support, such as

public class Message extends ModelObject {
...
}

public class ModelObject {

private final PropertyChangeSupport propertyChangeSupport = new
PropertyChangeSupport(
this);

public void addPropertyChangeListener(PropertyChangeListener listener) {
propertyChangeSupport.addPropertyChangeListener(listener);
}

public void addPropertyChangeListener(String propertyName,
PropertyChangeListener listener) {
propertyChangeSupport.addPropertyChangeListener(propertyName , listener);
}

public void removePropertyChangeListener(PropertyChangeListener listener)
{
propertyChangeSupport.removePropertyChangeListener(listener) ;
}

public void removePropertyChangeListener(String propertyName,
PropertyChangeListener listener) {
propertyChangeSupport.removePropertyChangeListener(propertyN ame,
listener);
}

protected void firePropertyChange(String propertyName, Object oldValue,
Object newValue) {
propertyChangeSupport.firePropertyChange(propertyName, oldValue,
newValue);
}
protected void fireIndexedPropertyChange(String propertyName, int index,
Object oldValue, Object newValue) {
propertyChangeSupport.fireIndexedPropertyChange( propertyName, index,
oldValue, newValue);
}
}

Report message to a moderator

Re: Why is it needed for java bean to implement property change support [message #328350 is a reply to message #328349]

Thu, 22 May 2008 17:17

Matthew Hall

Messages: 368
Registered: July 2009

Senior Member

hao wrote:
> jface databinding framwork has provided a lot of help classes, such as
> BeansObservables and WritableValue. Why is it still needed for java bean
> to implement property change support, such as
> <<snip>>

DataBinding is based around the observer pattern. If there is no
property change support on your bean, then BeansObservables has no way
to add property change listeners, and therefore cannot detect when your
bean properties change.

If property change support is not critical to your application, you can
use PojoObservables instead. PojoObservables are identical to
BeansObservables except that they do not use property change listeners.

Matthew

Report message to a moderator

[DataBinding] Re: Why is it needed for java bean to implement property change support [message #328351 is a reply to message #328349]

Thu, 22 May 2008 16:19

Eclipse User

Originally posted by: eclipse-news.rizzoweb.com

hao wrote:
> jface databinding framwork has provided a lot of help classes, such as
> BeansObservables and WritableValue. Why is it still needed for java bean
> to implement property change support

In Eclipse 3.4, there is a new class,
org.eclipse.core.databinding.beans.PojoObservables, that supports
creating observables on objects that do not fire property change events.
The limitation, of course, is that the framework isn't notified if the
underlying objects are changed directly - that's what the property
change events provide. So if your model objects don't do that they can't
tell the data binding framework when their properties have changed.

Hope this helps,
Eric

Report message to a moderator