com.sun.javafx.binding.FlatMappedBinding Maven / Gradle / Ivy
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package com.sun.javafx.binding;
import java.util.Objects;
import java.util.function.Function;
import javafx.beans.value.ObservableValue;
import javafx.util.Subscription;
/**
* A binding holding the value of an indirect source. The indirect source results from
* applying a mapping to the given source.
*
* Implementation:
*
*
In a flat mapped binding there are always two subscriptions involved:
*
* - The subscription on its source
* - The subscription on the value resulting from the mapping of the source: the indirect source
*
* The subscription on its given source is present when this binding itself is observed and not present otherwise.
*
* The subscription on the indirect source must change whenever the value of the given source changes or is invalidated. More
* specifically, when the given source is invalidated the indirect subscription should be removed, and when it is revalidated it
* should resubscribe to the newly calculated indirect source. The binding avoids resubscribing when only the value of
* the indirect source changes.
*
* @param the type of the source
* @param the type of the resulting binding
*/
public class FlatMappedBinding extends LazyObjectBinding {
private final ObservableValue source;
private final Function> mapper;
private Subscription indirectSourceSubscription = Subscription.EMPTY;
private ObservableValue indirectSource;
public FlatMappedBinding(ObservableValue source, Function> mapper) {
this.source = Objects.requireNonNull(source, "source cannot be null");
this.mapper = Objects.requireNonNull(mapper, "mapper cannot be null");
}
@Override
protected T computeValue() {
S value = source.getValue();
ObservableValue newIndirectSource = value == null ? null : mapper.apply(value);
if (isObserved() && indirectSource != newIndirectSource) { // only resubscribe when observed and the indirect source changed
indirectSourceSubscription.unsubscribe();
indirectSourceSubscription = newIndirectSource == null ? Subscription.EMPTY : newIndirectSource.subscribe(this::invalidate);
indirectSource = newIndirectSource;
}
return newIndirectSource == null ? null : newIndirectSource.getValue();
}
@Override
protected Subscription observeSources() {
Subscription subscription = source.subscribe(this::invalidateAll);
return () -> {
subscription.unsubscribe();
unsubscribeIndirectSource();
};
}
/**
* Called when the primary source changes. Invalidates this binding and unsubscribes the indirect source
* to avoid holding a strong reference to it. If the binding becomes valid later, {@link #computeValue()} will
* subscribe to a newly calculated indirect source.
*
* Note that this only needs to be called for changes of the primary source; changes in the indirect
* source only need to invalidate this binding without also unsubscribing, as it would be wasteful to resubscribe
* to the same indirect source for each invalidation of that source.
*/
private void invalidateAll() {
unsubscribeIndirectSource();
invalidate();
}
private void unsubscribeIndirectSource() {
indirectSourceSubscription.unsubscribe();
indirectSourceSubscription = Subscription.EMPTY;
indirectSource = null;
}
}