WeakChangeListener (JavaFX 12)

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 which can occur if observers are not unregistered from observed objects after use.
WeakChangeListener instances 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 for as long as it is in use, otherwise it will be garbage collected too soon.

Since:

JavaFX 2.0

See Also:

ChangeListener, ObservableValue

Constructor Summary

Constructors
Constructor Description

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

Method Summary

All Methods Instance Methods Concrete Methods
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 Detail
  - WeakChangeListener
```
public WeakChangeListener(ChangeListener<T> listener)
```
    The constructor of WeakChangeListener.
    
    Parameters:
    
    listener - The original listener that should be notified
- Method Detail
  - 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, it 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