com.jfoenix.controls.pannable.base.ResilientObservable Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 com.jfoenix.controls.pannable.base;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.function.Consumer;
import java.util.stream.Collectors;
/**
* Implementation of observer pattern using weak references
*
* @author Shadi Shaheen
* @version 1.0
* @since 2020-04-30
*/
public class ResilientObservable implements IObservableObject {
private CopyOnWriteArrayList> listeners = new CopyOnWriteArrayList<>();
public ResilientObservable() {
}
public boolean addListener(L observer) {
return listeners.add(new WeakObject<>(observer));
}
public boolean removeListener(L observer) {
return listeners.remove(new WeakObject<>(observer));
}
public void fireEvent(Consumer listenerConsumer) {
ArrayList> toBeRemoved = new ArrayList<>();
for (Iterator> itr = listeners.iterator(); itr.hasNext(); ) {
WeakObject ref = itr.next();
try {
// notify
L listener = ref.get();
if (listener != null) {
listenerConsumer.accept(listener);
} else {
toBeRemoved.add(ref);
}
} catch (RuntimeException e) {
e.printStackTrace();
toBeRemoved.add(ref);
}
}
// remove null / invalid references
listeners.removeAll(toBeRemoved);
}
public Collection listeners() {
return Collections.unmodifiableCollection(
listeners.stream().map(Reference::get).collect(Collectors.toList()));
}
private static class WeakObject extends WeakReference {
private WeakObject(T referent) {
super(referent);
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (obj == this) {
return true;
}
if (!(obj instanceof WeakObject)) {
return false;
}
return ((WeakObject) obj).get() == this.get();
}
}
}