Class ObjectBinding<T>

java.lang.Object
javafx.beans.binding.ObjectExpression<T>
javafx.beans.binding.ObjectBinding<T>
Type Parameters:
T - the type of the wrapped Object
All Implemented Interfaces:
Binding<T>, Observable, ObservableObjectValue<T>, ObservableValue<T>
public abstract class ObjectBinding<T> extends ObjectExpression<T> implements Binding<T>
Base class that provides most of the functionality needed to implement a Binding of an Object.

ObjectBinding provides a simple invalidation-scheme. An extending class can register dependencies by calling bind(Observable...). If One of the registered dependencies becomes invalid, this ObjectBinding is marked as invalid. With unbind(Observable...) listening to dependencies can be stopped.

To provide a concrete implementation of this class, the method computeValue() has to be implemented to calculate the value of this binding based on the current state of the dependencies. It is called when get() is called for an invalid binding.

See DoubleBinding for an example how this base class can be extended.

Since:
JavaFX 2.0
See Also:

  • Constructor Details

    • ObjectBinding

      public ObjectBinding()
      Creates a default ObjectBinding.

  • Method Details

    • addListener

      public void addListener(InvalidationListener listener)
      Description copied from interface: Observable
      Adds an InvalidationListener which will be notified whenever the Observable becomes invalid. 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 InvalidationListener instance may be safely registered for different Observables.

      The Observable 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 WeakInvalidationListener avoid this situation.

      Specified by:
      addListener in interface Observable
      Parameters:
      listener - The listener to register
      See Also:

    • removeListener

      public void removeListener(InvalidationListener listener)
      Description copied from interface: Observable
      Removes the given listener from the list of listeners, that are notified whenever the value of the Observable becomes invalid.

      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.

      Specified by:
      removeListener in interface Observable
      Parameters:
      listener - The listener to remove
      See Also:

    • addListener

      public void addListener(ChangeListener<? super T> listener)
      Description copied from interface: ObservableValue
      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.

      Specified by:
      addListener in interface ObservableValue<T>
      Parameters:
      listener - The listener to register
      See Also:

    • removeListener

      public void removeListener(ChangeListener<? super T> listener)
      Description copied from interface: ObservableValue
      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.

      Specified by:
      removeListener in interface ObservableValue<T>
      Parameters:
      listener - The listener to remove
      See Also:

    • bind

      protected final void bind(Observable... dependencies)
      Start observing the dependencies for changes. If the value of one of the dependencies changes, the binding is marked as invalid.
      Parameters:
      dependencies - the dependencies to observe

    • unbind

      protected final void unbind(Observable... dependencies)
      Stop observing the dependencies for changes.
      Parameters:
      dependencies - the dependencies to stop observing

    • dispose

      public void dispose()
      A default implementation of dispose() that is empty.
      Specified by:
      dispose in interface Binding<T>

    • getDependencies

      public ObservableList<?> getDependencies()
      A default implementation of getDependencies() that returns an empty ObservableList.
      Specified by:
      getDependencies in interface Binding<T>
      Returns:
      an empty ObservableList

    • get

      public final T get()
      Returns the result of computeValue(). The method computeValue() is only called if the binding is invalid. The result is cached and returned if the binding did not become invalid since the last call of get().
      Specified by:
      get in interface ObservableObjectValue<T>
      Returns:
      the current value

    • onInvalidating

      protected void onInvalidating()
      Called when this binding becomes invalid. Can be overridden by extending classes to react to the invalidation. The default implementation is empty.

    • invalidate

      public final void invalidate()
      Description copied from interface: Binding
      Mark a binding as invalid. This forces the recalculation of the value of the Binding next time it is request.
      Specified by:
      invalidate in interface Binding<T>

    • isValid

      public final boolean isValid()
      Description copied from interface: Binding
      Checks if a binding is valid.
      Specified by:
      isValid in interface Binding<T>
      Returns:
      true if the Binding is valid, false otherwise

    • isObserved

      protected final boolean isObserved()
      Checks if the binding has at least one listener registered on it. This is useful for subclasses which want to conserve resources when not observed.
      Returns:
      true if this binding currently has one or more listeners registered on it, otherwise false
      Since:
      19

    • allowValidation

      protected boolean allowValidation()
      Checks if the binding is allowed to become valid. Overriding classes can prevent a binding from becoming valid. This is useful in subclasses which do not always listen for invalidations of their dependencies and prefer to recompute the current value instead. This can also be useful if caching of the current computed value is not desirable.

      The default implementation always allows bindings to become valid.

      Returns:
      true if this binding is allowed to become valid, otherwise false
      Since:
      19

    • computeValue

      protected abstract T computeValue()
      Calculates the current value of this binding.

      Classes extending ObjectBinding have to provide an implementation of computeValue.

      Returns:
      the current value

    • toString

      public String toString()
      Returns a string representation of this ObjectBinding object.
      Overrides:
      toString in class Object
      Returns:
      a string representation of this ObjectBinding object.