Eclipse Platform
Release 3.3

org.eclipse.core.databinding.observable.value
Class ComputedValue

java.lang.Object
  extended byorg.eclipse.core.databinding.observable.ChangeManager
      extended byorg.eclipse.core.databinding.observable.AbstractObservable
          extended byorg.eclipse.core.databinding.observable.value.AbstractObservableValue
              extended byorg.eclipse.core.databinding.observable.value.ComputedValue
All Implemented Interfaces:
IObservable, IObservableValue

public abstract class ComputedValue
extends AbstractObservableValue

A Lazily calculated value that automatically computes and registers listeners on its dependencies as long as all of its dependencies are IObservable objects

This class is thread safe. All state accessing methods must be invoked from the current realm. Methods for adding and removing listeners may be invoked from any thread.

Since:
1.0

Constructor Summary
ComputedValue()
           
ComputedValue(Object valueType)
           
ComputedValue(Realm realm)
           
ComputedValue(Realm realm, Object valueType)
           
 
Method Summary
 void addChangeListener(IChangeListener listener)
          Adds the given change listener to the list of change listeners.
 void addValueChangeListener(IValueChangeListener listener)
           
protected abstract  Object calculate()
          Subclasses must override this method to provide the object's value.
 void dispose()
          Disposes of this observable object, removing all listeners registered with this object, and all listeners this object might have registered on other objects.
protected  Object doGetValue()
           
 Object getValueType()
          The value type of this observable value, or null if this observable value is untyped.
 boolean isStale()
          Returns whether the state of this observable is stale and is expected to change soon.
protected  void makeDirty()
           
 
Methods inherited from class org.eclipse.core.databinding.observable.value.AbstractObservableValue
doSetValue, fireChange, fireValueChange, getValue, removeValueChangeListener, setValue
 
Methods inherited from class org.eclipse.core.databinding.observable.AbstractObservable
addListener, addStaleListener, checkRealm, fireEvent, fireStale, firstListenerAdded, getRealm, hasListeners, lastListenerRemoved, removeChangeListener, removeListener, removeStaleListener
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface org.eclipse.core.databinding.observable.IObservable
addStaleListener, getRealm, removeChangeListener, removeStaleListener
 

Constructor Detail

ComputedValue

public ComputedValue()

ComputedValue

public ComputedValue(Object valueType)
Parameters:
valueType - can be null

ComputedValue

public ComputedValue(Realm realm)
Parameters:
realm -

ComputedValue

public ComputedValue(Realm realm,
                     Object valueType)
Parameters:
realm -
valueType -
Method Detail

doGetValue

protected final Object doGetValue()
Specified by:
doGetValue in class AbstractObservableValue

calculate

protected abstract Object calculate()
Subclasses must override this method to provide the object's value.

Returns:
the object's value

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

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

addValueChangeListener

public void addValueChangeListener(IValueChangeListener listener)
Specified by:
addValueChangeListener in interface IObservableValue
Overrides:
addValueChangeListener in class AbstractObservableValue

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 AbstractObservableValue

Eclipse Platform
Release 3.3

Guidelines for using Eclipse APIs.

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