javafx.event.WeakEventHandler Maven / Gradle / Ivy
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package javafx.event;
import java.lang.ref.WeakReference;
import javafx.beans.NamedArg;
/**
* Used in event handler registration in place of its associated event handler.
* Its sole purpose is to break the otherwise strong reference between an event
* handler container and its associated event handler. While the container still
* holds strong reference to the registered {@code WeakEventHandler} proxy, the
* proxy itself references the original handler only weakly and so doesn't
* prevent it from being garbage collected. Until this weak reference is broken,
* any event notification received by the proxy is forwarded to the original
* handler.
*
* @param the event class this handler can handle
* @since JavaFX 8.0
*/
public final class WeakEventHandler
implements EventHandler {
private final WeakReference> weakRef;
/**
* Creates a new instance of {@code WeakEventHandler}.
*
* @param eventHandler the original event handler to which to forward event
* notifications
*/
public WeakEventHandler(final @NamedArg("eventHandler") EventHandler eventHandler) {
weakRef = new WeakReference<>(eventHandler);
}
/**
* Indicates whether the associated event handler has been garbage
* collected. Used by containers to detect when the storage of corresponding
* references to this {@code WeakEventHandler} is no longer necessary.
*
* @return {@code true} if the associated handler has been garbage
* collected, {@code false} otherwise
*/
public boolean wasGarbageCollected() {
return weakRef.get() == null;
}
/**
* Forwards event notification to the associated event handler.
*
* @param event the event which occurred
*/
@Override
public void handle(final T event) {
final EventHandler eventHandler = weakRef.get();
if (eventHandler != null) {
eventHandler.handle(event);
}
}
/* Used for testing. */
void clear() {
weakRef.clear();
}
}