T - The type of the wrapped value.public interface ObservableValue<T>
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.
ObservableBooleanValue,
ObservableDoubleValue,
ObservableFloatValue,
ObservableIntegerValue,
ObservableLongValue,
ObservableNumberValue,
ObservableObjectValue,
ObservableStringValue| 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. |
void addListener(ChangeListener<? super T> listener)
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.
listener - The listener to registerjava.lang.NullPointerException - if the listener is nullremoveListener(ChangeListener)void removeListener(ChangeListener<? super T> listener)
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.
listener - The listener to removejava.lang.NullPointerException - if the listener is nulladdListener(ChangeListener)T getValue()
ObservableValue