javafx.beans.value

Interface ObservableValue<T>

Type Parameters:

T - The type of the wrapped value.

All Superinterfaces:

All Known Subinterfaces:

Binding<T>, JavaBeanProperty<T>, NumberBinding, NumberExpression, ObservableBooleanValue, ObservableDoubleValue, ObservableFloatValue, ObservableIntegerValue, ObservableListValue<E>, ObservableLongValue, ObservableMapValue<K,V>, ObservableNumberValue, ObservableObjectValue<T>, ObservableSetValue<E>, ObservableStringValue, Property<T>, ReadOnlyJavaBeanProperty<T>, ReadOnlyProperty<T>, TextInputControl.Content

All Known Implementing Classes:

public interface ObservableValue<T>
extends Observable

An ObservableValue is an entity that wraps a value and allows to observe the value for changes. In general this interface should not be implemented directly but one of its sub-interfaces ( ObservableBooleanValue etc.).

The value of the ObservableValue can be requested with getValue().

An implementation of ObservableValue may support lazy evaluation, which means that the value is not immediately recomputed after changes, but lazily the next time the value is requested. All bindings and properties in this library support lazy evaluation.

An ObservableValue generates two types of events: change events and invalidation events. A change event indicates that the value has changed. An invalidation event is generated, if the current value is not valid anymore. This distinction becomes important, if the ObservableValue supports lazy evaluation, because for a lazily evaluated value one does not know if an invalid value really has changed until it is recomputed. For this reason, generating change events requires eager evaluation while invalidation events can be generated for eager and lazy implementations.

Implementations of this class should strive to generate as few events as possible to avoid wasting too much time in event handlers. Implementations in this library mark themselves as invalid when the first invalidation event occurs. They do not generate anymore invalidation events until their value is recomputed and valid again.

Two types of listeners can be attached to an ObservableValue: InvalidationListener to listen to invalidation events and ChangeListener to listen to change events.

Important note: attaching a ChangeListener enforces eager computation even if the implementation of the ObservableValue supports lazy evaluation.

Since:

JavaFX 2.0

Method Summary

All MethodsInstance MethodsAbstract Methods
Modifier and Type	Method and Description
`void`	`addListener(ChangeListener<? super T> listener)` Adds a `ChangeListener` which will be notified whenever the value of the `ObservableValue` changes.
`T`	`getValue()` Returns the current value of this `ObservableValue`
`void`	`removeListener(ChangeListener<? super T> listener)` Removes the given listener from the list of listeners, that are notified whenever the value of the `ObservableValue` changes.

Methods inherited from interface javafx.beans.Observable
addListener, removeListener

Method Detail
- addListener
```
void addListener(ChangeListener<? super T> listener)
```
  Adds a ChangeListener which will be notified whenever the value of the ObservableValue changes. If the same listener is added more than once, then it will be notified more than once. That is, no check is made to ensure uniqueness.
  Note that the same actual ChangeListener instance may be safely registered for different ObservableValues.
  
  The ObservableValue stores a strong reference to the listener which will prevent the listener from being garbage collected and may result in a memory leak. It is recommended to either unregister a listener by calling removeListener after use or to use an instance of WeakChangeListener avoid this situation.
  
  Parameters:
  
  listener - The listener to register
  
  Throws:
  
  NullPointerException - if the listener is null
  
  See Also:
  
  removeListener(ChangeListener)
- removeListener
```
void removeListener(ChangeListener<? super T> listener)
```
  Removes the given listener from the list of listeners, that are notified whenever the value of the ObservableValue changes.
  If the given listener has not been previously registered (i.e. it was never added) then this method call is a no-op. If it had been previously added then it will be removed. If it had been added more than once, then only the first occurrence will be removed.
  
  Parameters:
  
  listener - The listener to remove
  
  Throws:
  
  NullPointerException - if the listener is null
  
  See Also:
  
  addListener(ChangeListener)
- getValue
```
T getValue()
```
  Returns the current value of this ObservableValue
  
  Returns:
  
  The current value

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Documentation extracted from JavaFX API Documentation.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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Interface ObservableValue<T>

Method Summary

Methods inherited from interface javafx.beans.Observable

Method Detail

addListener

removeListener

getValue