CompositeOnPageChangeCallback.java
/*
* Copyright 2019 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 androidx.viewpager2.widget;
import androidx.annotation.NonNull;
import androidx.annotation.Px;
import androidx.viewpager2.widget.ViewPager2.OnPageChangeCallback;
import java.util.ArrayList;
import java.util.ConcurrentModificationException;
import java.util.List;
/**
* Dispatches {@link OnPageChangeCallback} events to subscribers.
*/
final class CompositeOnPageChangeCallback extends OnPageChangeCallback {
@NonNull
private final List<OnPageChangeCallback> mCallbacks;
CompositeOnPageChangeCallback(int initialCapacity) {
mCallbacks = new ArrayList<>(initialCapacity);
}
/**
* Adds the given callback to the list of subscribers
*/
void addOnPageChangeCallback(OnPageChangeCallback callback) {
mCallbacks.add(callback);
}
/**
* Removes the given callback from the list of subscribers
*/
void removeOnPageChangeCallback(OnPageChangeCallback callback) {
mCallbacks.remove(callback);
}
/**
* @see OnPageChangeCallback#onPageScrolled(int, float, int)
*/
@Override
public void onPageScrolled(int position, float positionOffset, @Px int positionOffsetPixels) {
try {
for (OnPageChangeCallback callback : mCallbacks) {
callback.onPageScrolled(position, positionOffset, positionOffsetPixels);
}
} catch (ConcurrentModificationException ex) {
throwCallbackListModifiedWhileInUse(ex);
}
}
/**
* @see OnPageChangeCallback#onPageSelected(int)
*/
@Override
public void onPageSelected(int position) {
try {
for (OnPageChangeCallback callback : mCallbacks) {
callback.onPageSelected(position);
}
} catch (ConcurrentModificationException ex) {
throwCallbackListModifiedWhileInUse(ex);
}
}
/**
* @see OnPageChangeCallback#onPageScrollStateChanged(int)
*/
@Override
public void onPageScrollStateChanged(@ViewPager2.ScrollState int state) {
try {
for (OnPageChangeCallback callback : mCallbacks) {
callback.onPageScrollStateChanged(state);
}
} catch (ConcurrentModificationException ex) {
throwCallbackListModifiedWhileInUse(ex);
}
}
private void throwCallbackListModifiedWhileInUse(ConcurrentModificationException parent) {
throw new IllegalStateException(
"Adding and removing callbacks during dispatch to callbacks is not supported",
parent
);
}
}