javafx.beans.binding.DoubleBinding Maven / Gradle / Ivy
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package javafx.beans.binding;
import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.beans.value.ChangeListener;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import com.sun.javafx.binding.BindingHelperObserver;
import com.sun.javafx.binding.ExpressionHelper;
/**
* Base class that provides most of the functionality needed to implement a
* {@link Binding} of a {@code double} value.
*
* {@code DoubleBinding} provides a simple invalidation-scheme. An extending
* class can register dependencies by calling {@link #bind(Observable...)}.
* If One of the registered dependencies becomes invalid, this
* {@code DoubleBinding} is marked as invalid. With
* {@link #unbind(Observable...)} listening to dependencies can be stopped.
*
* To provide a concrete implementation of this class, the method
* {@link #computeValue()} has to be implemented to calculate the value of this
* binding based on the current state of the dependencies. It is called when
* {@link #get()} is called for an invalid binding.
*
* Below is a simple example of a {@code DoubleBinding} calculating the square-
* root of a {@link javafx.beans.value.ObservableNumberValue} {@code moo}.
*
*
*
* final ObservableDoubleValue moo = ...;
*
* DoubleBinding foo = new DoubleBinding() {
*
* {
* super.bind(moo);
* }
*
* @Override
* protected double computeValue() {
* return Math.sqrt(moo.getValue());
* }
* };
*
*
*
* Following is the same example with implementations for the optional methods
* {@link Binding#getDependencies()} and {@link Binding#dispose()}.
*
*
*
* final ObservableDoubleValue moo = ...;
*
* DoubleBinding foo = new DoubleBinding() {
*
* {
* super.bind(moo);
* }
*
* @Override
* protected double computeValue() {
* return Math.sqrt(moo.getValue());
* }
*
* @Override
* public ObservableList<?> getDependencies() {
* return FXCollections.singletonObservableList(moo);
* }
*
* @Override
* public void dispose() {
* super.unbind(moo);
* }
* };
*
*
*
* @see Binding
* @see NumberBinding
* @see javafx.beans.binding.DoubleExpression
*
*
* @since JavaFX 2.0
*/
public abstract class DoubleBinding extends DoubleExpression implements
NumberBinding {
private double value;
private boolean valid;
/**
* Invalidation listener used for observing dependencies. This
* is never cleared once created as there is no way to determine
* when all dependencies that were previously bound were removed
* in one or more calls to {@link #unbind(Observable...)}.
*/
private BindingHelperObserver observer;
private ExpressionHelper helper = null;
/**
* Creates a default {@code DoubleBinding}.
*/
public DoubleBinding() {
}
@Override
public void addListener(InvalidationListener listener) {
helper = ExpressionHelper.addListener(helper, this, listener);
}
@Override
public void removeListener(InvalidationListener listener) {
helper = ExpressionHelper.removeListener(helper, listener);
}
@Override
public void addListener(ChangeListener listener) {
helper = ExpressionHelper.addListener(helper, this, listener);
}
@Override
public void removeListener(ChangeListener listener) {
helper = ExpressionHelper.removeListener(helper, listener);
}
/**
* Start observing the dependencies for changes. If the value of one of the
* dependencies changes, the binding is marked as invalid.
*
* @param dependencies
* the dependencies to observe
*/
protected final void bind(Observable... dependencies) {
if ((dependencies != null) && (dependencies.length > 0)) {
if (observer == null) {
observer = new BindingHelperObserver(this);
}
for (final Observable dep : dependencies) {
dep.addListener(observer);
}
}
}
/**
* Stop observing the dependencies for changes.
*
* @param dependencies
* the dependencies to stop observing
*/
protected final void unbind(Observable... dependencies) {
if (observer != null) {
for (final Observable dep : dependencies) {
dep.removeListener(observer);
}
}
}
/**
* A default implementation of {@code dispose()} that is empty.
*/
@Override
public void dispose() {
}
/**
* A default implementation of {@code getDependencies()} that returns an
* empty {@link javafx.collections.ObservableList}.
*
* @return an empty {@code ObservableList}
*/
@Override
public ObservableList getDependencies() {
return FXCollections.emptyObservableList();
}
/**
* Returns the result of {@link #computeValue()}. The method
* {@code 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 {@code get()}.
*
* @return the current value
*/
@Override
public final double get() {
if (!valid) {
value = computeValue();
valid = true;
}
return value;
}
/**
* The method onInvalidating() can be overridden by extending classes to
* react, if this binding becomes invalid. The default implementation is
* empty.
*/
protected void onInvalidating() {
}
@Override
public final void invalidate() {
if (valid) {
valid = false;
onInvalidating();
ExpressionHelper.fireValueChangedEvent(helper);
}
}
@Override
public final boolean isValid() {
return valid;
}
/**
* Calculates the current value of this binding.
*
* Classes extending {@code DoubleBinding} have to provide an implementation
* of {@code computeValue}.
*
* @return the current value
*/
protected abstract double computeValue();
/**
* Returns a string representation of this {@code DoubleBinding} object.
* @return a string representation of this {@code DoubleBinding} object.
*/
@Override
public String toString() {
return valid ? "DoubleBinding [value: " + get() + "]"
: "DoubleBinding [invalid]";
}
}