Package org.eclipse.core.databinding.observable.value

Class DuplexingObservableValue<T>

  • Type Parameters:
    T - the type of value being observed
    All Implemented Interfaces:
    IObservable, IObservableValue<T>
    public abstract class DuplexingObservableValue<T>
extends AbstractObservableValue<T>
    A class to reduce an observable list to a single value in an implementation specific way.

    A concrete implementation must implement coalesceElements(Collection) to specify how the current state of the observed list is reduced to a single value.

    For example the default implementation in withDefaults(IObservableList, Object, Object) will return a predefined empty value in case the observed list is empty, an predefined multi value if the list contains multiple different values and the list value if it is the only value or all list values are equal.

    Since:
    1.2

    • Constructor Detail

      • DuplexingObservableValue

        public DuplexingObservableValue​(IObservableList<T> target)
        Parameters:
        target - the observed target list

      • DuplexingObservableValue

        public DuplexingObservableValue​(IObservableList<T> target,
                                Object valueType)
        Parameters:
        target - the observed target list
        valueType - the value type or null

    • Method Detail

      • withDefaults

        public static <T> DuplexingObservableValue<T> withDefaults​(IObservableList<T> target,
                                                           T emptyValue,
                                                           T multiValue)
        Returns a DuplexingObservableValue implementation with predefined values to use if the list is empty or contains multiple different values.
        Type Parameters:
        T - the type of value being observed
        Parameters:
        target - the observable list
        emptyValue - the value to use when the target list is empty
        multiValue - the value to use when the target list contains multiple values that are not equivalent to each other.
        Returns:
        a DuplexingObservableValue implementation with predefined values to use if the list is empty or contains multiple different values.

      • firstListenerAdded

        protected void firstListenerAdded()

      • lastListenerRemoved

        protected void lastListenerRemoved()

      • makeDirty

        protected final void makeDirty()

      • isStale

        public boolean isStale()
        Description copied from interface: IObservable
        Returns whether the state of this observable is stale and is expected to change soon. A non-stale observable that becomes stale will notify its stale listeners. A stale object that becomes non-stale does so by changing its state and notifying its change listeners, it does not notify its stale listeners about becoming non-stale. Clients that do not expect asynchronous changes may ignore staleness of observable objects.
        Specified by:
        isStale in interface IObservable
        Overrides:
        isStale in class AbstractObservableValue<T>
        Returns:
        true if this observable's state is stale and will change soon.

      • coalesceElements

        protected abstract T coalesceElements​(Collection<T> elements)
        Called when the current value of this class is requested. The implementation must calculate a single value which should represent the given elements.
        Parameters:
        elements - the collection of elements to be coalesced
        Returns:
        the value representing the elements

      • getValueType

        public Object getValueType()
        Description copied from interface: IObservableValue
        The value type of this observable value, or null if this observable value is untyped.
        Returns:
        the value type, or null

      • addChangeListener

        public void addChangeListener​(IChangeListener listener)
        Description copied from interface: IObservable
        Adds the given change listener to the list of change listeners. Change listeners are notified about changes of the state of this observable in a generic way, without specifying the change that happened. To get the changed state, a change listener needs to query for the current state of this observable.
        Specified by:
        addChangeListener in interface IObservable
        Overrides:
        addChangeListener in class AbstractObservable
        Parameters:
        listener - the listener to add; not null

      • dispose

        public void dispose()
        Description copied from interface: IObservable
        Disposes of this observable object, removing all listeners registered with this object, and all listeners this object might have registered on other objects.
        Specified by:
        dispose in interface IObservable
        Overrides:
        dispose in class AbstractObservable

      • addListener

        protected void addListener​(Object listenerType,
                           IObservablesListener listener)
        Parameters:
        listenerType - arbitrary object to identify a type of the listener
        listener - the listener to add; not null

      • removeListener

        protected void removeListener​(Object listenerType,
                              IObservablesListener listener)
        Parameters:
        listenerType - arbitrary object to identify a type of the listener
        listener - the listener to remove; not null

      • hasListeners

        protected boolean hasListeners()

      • getRealm

        public Realm getRealm()
        Returns:
        Returns the realm.