Package javafx.beans.value

Class WeakChangeListener<T>

java.lang.Object

javafx.beans.value.WeakChangeListener<T>

Type Parameters:

T - The type of the observed value

All Implemented Interfaces:

ChangeListener<T>, WeakListener

public final class WeakChangeListener<T>
extends Object
implements ChangeListener<T>, WeakListener

A WeakChangeListener can be used, if an ObservableValue should only maintain a weak reference to the listener. This helps to avoid memory leaks, that can occur if observers are not unregistered from observed objects after use.

WeakChangeListener are created by passing in the original ChangeListener. The WeakChangeListener should then be registered to listen for changes of the observed object.

Note: You have to keep a reference to the ChangeListener, that was passed in as long as it is in use, otherwise it will be garbage collected to soon.

Since:

JavaFX 2.0

See Also:

• ChangeListener
• ObservableValue

Constructor Summary

Constructors

Constructor	Description
WeakChangeListener(ChangeListener<T> listener)	The constructor of WeakChangeListener.

Method Summary

Modifier and Type	Method	Description
void	changed(ObservableValue<? extends T> observable, T oldValue, T newValue)	This method needs to be provided by an implementation of ChangeListener.
boolean	wasGarbageCollected()	Returns true if the linked listener was garbage-collected.

Methods inherited from class java.lang.Object

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

Constructor Details

WeakChangeListener

public WeakChangeListener(ChangeListener<T> listener)

The constructor of WeakChangeListener.

Parameters:

listener - The original listener that should be notified

Method Details

wasGarbageCollected

public boolean wasGarbageCollected()

Returns true if the linked listener was garbage-collected. In this case, the listener can be removed from the observable.

Specified by:

wasGarbageCollected in interface WeakListener

Returns:

true if the linked listener was garbage-collected.

changed

public void changed(ObservableValue<? extends T> observable,
 T oldValue,
 T newValue)

This method needs to be provided by an implementation of ChangeListener. It is called if the value of an ObservableValue changes.

In general is is considered bad practice to modify the observed value in this method.

Specified by:

changed in interface ChangeListener<T>

Parameters:

observable - The ObservableValue which value changed

oldValue - The old value

newValue - The new value