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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.mozilla.thirdparty.com.google.android.exoplayer2.util;
import android.os.Handler;
import java.util.concurrent.CopyOnWriteArrayList;
/**
* Event dispatcher which allows listener registration.
*
* @param <T> The type of listener.
*/
public final class EventDispatcher<T> {
/** Functional interface to send an event. */
public interface Event<T> {
/**
* Sends the event to a listener.
*
* @param listener The listener to send the event to.
*/
void sendTo(T listener);
}
/** The list of listeners and handlers. */
private final CopyOnWriteArrayList<HandlerAndListener<T>> listeners;
/** Creates an event dispatcher. */
public EventDispatcher() {
listeners = new CopyOnWriteArrayList<>();
}
/** Adds a listener to the event dispatcher. */
public void addListener(Handler handler, T eventListener) {
Assertions.checkArgument(handler != null && eventListener != null);
removeListener(eventListener);
listeners.add(new HandlerAndListener<>(handler, eventListener));
}
/** Removes a listener from the event dispatcher. */
public void removeListener(T eventListener) {
for (HandlerAndListener<T> handlerAndListener : listeners) {
if (handlerAndListener.listener == eventListener) {
handlerAndListener.release();
listeners.remove(handlerAndListener);
}
}
}
/**
* Dispatches an event to all registered listeners.
*
* @param event The {@link Event}.
*/
public void dispatch(Event<T> event) {
for (HandlerAndListener<T> handlerAndListener : listeners) {
handlerAndListener.dispatch(event);
}
}
private static final class HandlerAndListener<T> {
private final Handler handler;
private final T listener;
private boolean released;
public HandlerAndListener(Handler handler, T eventListener) {
this.handler = handler;
this.listener = eventListener;
}
public void release() {
released = true;
}
public void dispatch(Event<T> event) {
handler.post(
() -> {
if (!released) {
event.sendTo(listener);
}
});
}
}
}
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