PageTransformerAdapter.java
/*
* Copyright 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 androidx.viewpager2.widget;
import android.view.View;
import androidx.annotation.Nullable;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.viewpager2.widget.ViewPager2.OnPageChangeCallback;
import androidx.viewpager2.widget.ViewPager2.PageTransformer;
import java.util.Locale;
/**
* Translates {@link OnPageChangeCallback} events to {@link PageTransformer} events.
*/
final class PageTransformerAdapter extends OnPageChangeCallback {
private final LinearLayoutManager mLayoutManager;
private PageTransformer mPageTransformer;
PageTransformerAdapter(LinearLayoutManager layoutManager) {
mLayoutManager = layoutManager;
}
PageTransformer getPageTransformer() {
return mPageTransformer;
}
/**
* Sets the PageTransformer. The page transformer will be called for each attached page whenever
* the scroll position is changed.
*
* @param transformer The PageTransformer
*/
void setPageTransformer(@Nullable PageTransformer transformer) {
// TODO: add support for reverseDrawingOrder: b/112892792
// TODO: add support for pageLayerType: b/112893074
mPageTransformer = transformer;
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
if (mPageTransformer == null) {
return;
}
float transformOffset = -positionOffset;
for (int i = 0; i < mLayoutManager.getChildCount(); i++) {
View view = mLayoutManager.getChildAt(i);
if (view == null) {
throw new IllegalStateException(String.format(Locale.US,
"LayoutManager returned a null child at pos %d/%d while transforming pages",
i, mLayoutManager.getChildCount()));
}
int currPos = mLayoutManager.getPosition(view);
float viewOffset = transformOffset + (currPos - position);
mPageTransformer.transformPage(view, viewOffset);
}
}
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
}