On 25 juil, 10:50, "david.herv...@gmail.com" <david.herv...@gmail.com>
wrote:
> Hi,
>
> I'm facing a problem when using the simple implementation of the
> EventBus.
>
> // register widget B to be notified when WidgetA trigger an event
> register handler of WidgetB on WidgetA.EventType
>
> // dispatch (firingDepth is incremented)
> WidgetA.fireEvent
>
> // my widget is really called !!! that's good news
> WidgetB.onWidgetAEvent
>
> // on the WidgetA.EventType reception is decided to create a widget C
> create widgetC
>
> // this widget register himself to be notified on widgetB events ->
> here the widget is registered in the deferredDeltas map (enqueueing)
> register handler of widgetC on WidgetB.EventType
>
> // widget B fired an event which is never trapped by the widget C
> because the handler of Widget C is in the deferredDeltas AND
> firingDepth is not 0
> WidgetB.fireEvent
>
> I'm doubtful because I was expected Widget C to receive event from
> Widget B. A work around is to encapsulate the WidgetB.fireEvent into a
> DeferredCommand but it's not really a solution.
>
> An other solution is to reconsider the usage of firingDepth, I don't
> really know why it is used (actually I know, but avoid concurrency
> modification that way leads to the upper that strange behavior).
> In simple implementation (thread safe) will be to get rid of the usage
> of this firingDepth/deferredDeltas and that getHandlerList return a
> copy of the handlers to go through and that's it:
> We insert directly the handler when they request for registration and
> we fire on the current map of handlers
>
> Below is a possible implementation of what I think is a better
> implementation (behaviorally speaking) :
>
> package com.google.web.bindery.event.shared;
>
> import java.util.ArrayList;
> import java.util.Collections;
> import java.util.HashMap;
> import java.util.HashSet;
> import java.util.List;
> import java.util.ListIterator;
> import java.util.Map;
> import java.util.Set;
>
> import com.google.web.bindery.event.shared.Event.Type;
>
> public class MySimpleEventBus extends EventBus {
>
> private final boolean isReverseOrder;
>
> /**
> * Map of event type to map of event source to list of their
> handlers.
> */
> private final Map<Event.Type<?>, Map<Object, List<?>>> map =
> new HashMap<Event.Type<?>, Map<Object, List<?>>>();
>
> public MySimpleEventBus() {
> this(false);
> }
>
> /**
> * Allows creation of an instance that fires its handlers in the
> reverse of
> * the order in which they were added, although filtered handlers
> all fire
> * before unfiltered handlers.
> * <p>
> *
> * @deprecated This is a legacy feature, required by GWT's old
> HandlerManager.
> * Reverse order is not honored for handlers tied to a
> specific
> * event source (via {@link #addHandlerToSource}.
> */
> @Deprecated
> protected MySimpleEventBus(boolean fireInReverseOrder) {
> isReverseOrder = fireInReverseOrder;
> }
>
> @Override
> public <H> HandlerRegistration addHandler(Type<H> type, H handler)
> {
> return doAdd(type, null, handler);
> }
>
> @Override
> public <H> HandlerRegistration addHandlerToSource(final
> Event.Type<H> type, final Object source,
> final H handler) {
> if (source == null) {
> throw new NullPointerException("Cannot add a handler with a
> null source");
> }
>
> return doAdd(type, source, handler);
> }
>
> @Override
> public void fireEvent(Event<?> event) {
> doFire(event, null);
> }
>
> @Override
> public void fireEventFromSource(Event<?> event, Object source) {
> if (source == null) {
> throw new NullPointerException("Cannot fire from a null
> source");
> }
> doFire(event, source);
> }
>
> /**
> * @deprecated required by legacy features in GWT's old
> HandlerManager
> */
> @Deprecated
> protected <H> void doRemove(Event.Type<H> type, Object source, H
> handler) {
> doRemoveNow(type, source, handler);
> }
>
> /**
> * @deprecated required by legacy features in GWT's old
> HandlerManager
> */
> @Deprecated
> protected <H> H getHandler(Event.Type<H> type, int index) {
> assert index < getHandlerCount(type) : "handlers for " +
> type.getClass() + " have size: "
> + getHandlerCount(type) + " so do not have a handler at
> index: " + index;
>
> List<H> l = getHandlerList(type, null);
> return l.get(index);
> }
>
> /**
> * @deprecated required by legacy features in GWT's old
> HandlerManager
> */
> @Deprecated
> protected int getHandlerCount(Event.Type<?> eventKey) {
> return getHandlerList(eventKey, null).size();
> }
>
> /**
> * @deprecated required by legacy features in GWT's old
> HandlerManager
> */
> @Deprecated
> protected boolean isEventHandled(Event.Type<?> eventKey) {
> return map.containsKey(eventKey);
> }
>
> private <H> HandlerRegistration doAdd(final Event.Type<H> type,
> final Object source,
> final H handler) {
> if (type == null) {
> throw new NullPointerException("Cannot add a handler with a
> null type");
> }
> if (handler == null) {
> throw new NullPointerException("Cannot add a null handler");
> }
>
> doAddNow(type, source, handler);
>
> return new HandlerRegistration() {
> public void removeHandler() {
> doRemove(type, source, handler);
> }
> };
> }
>
> private <H> void doAddNow(Event.Type<H> type, Object source, H
> handler) {
> List<H> l = ensureHandlerList(type, source);
> l.add(handler);
> }
>
> private <H> void doFire(Event<H> event, Object source) {
> if (event == null) {
> throw new NullPointerException("Cannot fire null event");
> }
> try {
>
> if (source != null) {
> event.setSource(source);
> }
>
> List<H> handlers = getDispatchList(event.getAssociatedType(),
> source);
> Set<Throwable> causes = null;
>
> ListIterator<H> it =
> isReverseOrder ? handlers.listIterator(handlers.size()) :
> handlers.listIterator();
> while (isReverseOrder ? it.hasPrevious() : it.hasNext()) {
> H handler = isReverseOrder ? it.previous() : it.next();
>
> try {
> event.dispatch(handler);
> } catch (Throwable e) {
> if (causes == null) {
> causes = new HashSet<Throwable>();
> }
> causes.add(e);
> }
> }
>
> if (causes != null) {
> throw new UmbrellaException(causes);
> }
> } finally {
> // no more to do
> }
> }
>
> private <H> void doRemoveNow(Event.Type<H> type, Object source, H
> handler) {
> List<H> l = getHandlerList(type, source);
>
> boolean removed = l.remove(handler);
> assert removed : "redundant remove call";
> if (removed && l.isEmpty()) {
> prune(type, source);
> }
> }
>
> private <H> List<H> ensureHandlerList(Event.Type<H> type, Object
> source) {
> Map<Object, List<?>> sourceMap = map.get(type);
> if (sourceMap == null) {
> sourceMap = new HashMap<Object, List<?>>();
> map.put(type, sourceMap);
> }
>
> // safe, we control the puts.
> @SuppressWarnings("unchecked")
> List<H> handlers = (List<H>) sourceMap.get(source);
> if (handlers == null) {
> handlers = new ArrayList<H>();
> sourceMap.put(source, handlers);
> }
>
> return handlers;
> }
>
> /**
> * Return a copy of handlers to dispatch event to
> */
> private <H> List<H> getDispatchList(Event.Type<H> type, Object
> source) {
> List<H> directHandlers = getHandlerList(type, source);
> if (source == null) {
> return new ArrayList<H>(directHandlers);
> }
>
> List<H> globalHandlers = getHandlerList(type, null);
>
> List<H> rtn = new ArrayList<H>(directHandlers);
> rtn.addAll(globalHandlers);
> return rtn;
> }
>
> private <H> List<H> getHandlerList(Event.Type<H> type, Object
> source) {
> Map<Object, List<?>> sourceMap = map.get(type);
> if (sourceMap == null) {
> return Collections.emptyList();
> }
>
> // safe, we control the puts.
> @SuppressWarnings("unchecked")
> List<H> handlers = (List<H>) sourceMap.get(source);
> if (handlers == null) {
> return Collections.emptyList();
> }
>
> return handlers;
> }
>
> private void prune(Event.Type<?> type, Object source) {
> Map<Object, List<?>> sourceMap = map.get(type);
>
> List<?> pruned = sourceMap.remove(source);
>
> assert pruned != null : "Can't prune what wasn't there";
> assert pruned.isEmpty() : "Pruned unempty list!";
>
> if (sourceMap.isEmpty()) {
> map.remove(type);
> }
> }
>
> }
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