package com.tejia.lijin.app.util;
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import android.graphics.Rect;
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import androidx.recyclerview.widget.PagerSnapHelper;
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import androidx.recyclerview.widget.RecyclerView;
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import android.util.Log;
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import android.view.View;
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import android.view.ViewGroup;
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import java.lang.ref.WeakReference;
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/**
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* Created by yjwfn on 2017/9/21.
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*/
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public class ScalableCardHelper {
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private static final float STAY_SCALE = 0.88f;
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private String TAG = "ScalableCardHelper";
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private PagerSnapHelper snapHelper = new PagerSnapHelper();
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private RecyclerView recyclerView;
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private WeakReference<OnPageChangeListener> pageChangeListenerRef;
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private RecyclerView.OnScrollListener scrollListener = new RecyclerView.OnScrollListener() {
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@Override
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public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
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pageScrolled();
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}
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};
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public ScalableCardHelper(OnPageChangeListener pageChangeListener) {
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if (pageChangeListener != null)
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this.pageChangeListenerRef = new WeakReference<>(pageChangeListener);
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}
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public ScalableCardHelper() {
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this(null);
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}
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private void pageScrolled() {
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if (recyclerView == null || recyclerView.getChildCount() == 0)
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return;
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RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
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View snapingView = snapHelper.findSnapView(layoutManager);
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int snapingViewPosition = recyclerView.getChildAdapterPosition(snapingView);
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View leftSnapingView = layoutManager.findViewByPosition(snapingViewPosition - 1);
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View rightSnapingView = layoutManager.findViewByPosition(snapingViewPosition + 1);
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float leftSnapingOffset = calculateOffset(recyclerView, leftSnapingView);
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float rightSnapingOffset = calculateOffset(recyclerView, rightSnapingView);
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float currentSnapingOffset = calculateOffset(recyclerView, snapingView);
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if (snapingView != null) {
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snapingView.setScaleX(currentSnapingOffset);
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snapingView.setScaleY(currentSnapingOffset);
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}
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if (leftSnapingView != null) {
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leftSnapingView.setScaleX(leftSnapingOffset);
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leftSnapingView.setScaleY(leftSnapingOffset);
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}
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if (rightSnapingView != null) {
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rightSnapingView.setScaleX(rightSnapingOffset);
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rightSnapingView.setScaleY(rightSnapingOffset);
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}
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if (snapingView != null && currentSnapingOffset >= 1) {
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OnPageChangeListener listener = pageChangeListenerRef != null ? pageChangeListenerRef.get() : null;
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if (listener != null)
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listener.onPageSelected(snapingViewPosition);
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}
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Log.d(TAG, String.format("left: %f, right: %f, current: %f", leftSnapingOffset, rightSnapingOffset, currentSnapingOffset));
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}
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public int getCurrentPage() {
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View page = snapHelper.findSnapView(recyclerView.getLayoutManager());
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if (page == null)
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return -1;
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return recyclerView.getChildAdapterPosition(page);
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}
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public void attachToRecyclerView(final RecyclerView recyclerView) {
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this.recyclerView = recyclerView;
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snapHelper.attachToRecyclerView(recyclerView);
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recyclerView.addOnScrollListener(scrollListener);
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recyclerView.addItemDecoration(new ScalableCardItemDecoration());
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recyclerView.post(new Runnable() {
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@Override
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public void run() {
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pageScrolled();
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}
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});
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}
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/**
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* 通过计算{@code view}中间点与{@link RecyclerView}的中间点的距离，算出{@code view}的偏移量。
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*
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* @param view view
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* @return
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*/
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private float calculateOffset(RecyclerView recyclerView, View view) {
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if (view == null)
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return -1;
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RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
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boolean isVertical = layoutManager.canScrollVertically();
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int viewStart = isVertical ? view.getTop() : view.getLeft();
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int viewEnd = isVertical ? view.getBottom() : view.getRight();
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int centerX = isVertical ? recyclerView.getHeight() / 2 : recyclerView.getWidth() / 2;
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int childCenter = (viewStart + viewEnd) / 2;
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int distance = Math.abs(childCenter - centerX);
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if (distance > centerX)
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return STAY_SCALE;
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float offset = 1.f - (distance / (float) centerX);
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return (1.f - STAY_SCALE) * offset + STAY_SCALE;
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}
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public void detachFromRecyclerView(RecyclerView recyclerView) {
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if (recyclerView != null)
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recyclerView.removeOnScrollListener(scrollListener);
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this.recyclerView = null;
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}
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public interface OnPageChangeListener {
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void onPageSelected(int position);
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}
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public static int getPeekWidth(RecyclerView recyclerView, View itemView) {
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RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
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boolean isVertical = layoutManager.canScrollVertically();
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int position = recyclerView.getChildAdapterPosition(itemView);
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//TODO RecyclerView使用wrap_content时，获取的宽度可能会是0。
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int parentWidth = recyclerView.getMeasuredWidth();
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int parentHeight = recyclerView.getMeasuredHeight(); //有时会拿到0
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parentWidth = parentWidth == 0 ? recyclerView.getWidth() : parentWidth;
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parentHeight = parentHeight == 0 ? recyclerView.getHeight() : parentHeight;
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int parentEnd = isVertical ? parentHeight : parentWidth;
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int parentCenter = parentEnd / 2;
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int itemSize = isVertical ? itemView.getMeasuredHeight() : itemView.getMeasuredWidth();
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if (itemSize == 0) {
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ViewGroup.LayoutParams layoutParams = itemView.getLayoutParams();
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int widthMeasureSpec =
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RecyclerView.LayoutManager.getChildMeasureSpec(parentWidth,
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layoutManager.getWidthMode(),
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recyclerView.getPaddingLeft() + recyclerView.getPaddingRight(),
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layoutParams.width, layoutManager.canScrollHorizontally());
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int heightMeasureSpec =
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RecyclerView.LayoutManager.getChildMeasureSpec(parentHeight,
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layoutManager.getHeightMode(),
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recyclerView.getPaddingTop() + recyclerView.getPaddingBottom(),
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layoutParams.height, layoutManager.canScrollVertically());
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itemView.measure(widthMeasureSpec, heightMeasureSpec);
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itemSize = isVertical ? itemView.getMeasuredHeight() : itemView.getMeasuredWidth();
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}
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/*
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计算ItemDecoration的大小，确保插入的大小正好使view的start + itemSize / 2等于parentCenter。
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*/
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int startOffset = parentCenter - itemSize / 2;
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int endOffset = parentEnd - (startOffset + itemSize);
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return position == 0 ? startOffset : endOffset;
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}
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private static class ScalableCardItemDecoration extends RecyclerView.ItemDecoration {
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@Override
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public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
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RecyclerView.ViewHolder holder = parent.getChildViewHolder(view);
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int position = holder.getAdapterPosition() == RecyclerView.NO_POSITION ? holder.getOldPosition() : holder.getAdapterPosition();
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RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
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int itemCount = layoutManager.getItemCount();
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if (position != 0 && position != itemCount - 1) {
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return;
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}
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int peekWidth = getPeekWidth(parent, view);
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boolean isVertical = layoutManager.canScrollVertically();
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//移除item时adapter position为-1。
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if (isVertical) {
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if (position == 0) {
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outRect.set(0, peekWidth, 0, 0);
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} else if (position == itemCount - 1) {
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outRect.set(0, 0, 0, peekWidth);
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} else {
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outRect.set(0, 0, 0, 0);
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}
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} else {
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if (position == 0) {
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outRect.set(peekWidth, 0, 0, 0);
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} else if (position == itemCount - 1) {
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outRect.set(0, 0, peekWidth, 0);
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} else {
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outRect.set(0, 0, 0, 0);
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}
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}
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}
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}
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}
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