修复当 RecyclerView 被其他透明或半透明 View 遮挡时，LinearLayoutManager#findFirstVisibleItemPosition 等方法会失效的问题。

AdvancedLinearLayoutManager.java

import android.annotation.SuppressLint;
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;

import java.util.HashMap;
import java.util.Map;

import androidx.annotation.Nullable;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

/**
 * @author heruoxin @ CatchingNow Inc.
 * @since 2019-08-04
 */
public class AdvancedLinearLayoutManager extends LinearLayoutManager {

    @Nullable
    private RecyclerView rv;

    public AdvancedLinearLayoutManager(Context context) {
        super(context);
    }

    public AdvancedLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    public AdvancedLinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    public void onAttachedToWindow(RecyclerView view) {
        super.onAttachedToWindow(view);
        rv = view;
    }

    @Override
    public void onDetachedFromWindow(RecyclerView view, RecyclerView.Recycler recycler) {
        super.onDetachedFromWindow(view, recycler);
        rv = null;
    }

    // map of child adapter position to its height.
    @SuppressLint("UseSparseArrays")
    private Map<Integer, Integer> childSizesMap = new HashMap<>();

    @Override
    public void onLayoutCompleted(RecyclerView.State state) {
        super.onLayoutCompleted(state);
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            if (child != null) childSizesMap.put(getPosition(child), getDecoratedMeasuredHeight(child));
        }
    }

    @Override
    public int computeVerticalScrollOffset(RecyclerView.State state) {
        //return super.computeVerticalScrollOffset(state);

        if (getChildCount() == 0) return 0;
        int firstChildPosition = findFirstVisibleItemPosition();
        View firstChild = findViewByPosition(firstChildPosition);
        if (firstChild == null) return super.computeVerticalScrollOffset(state);
        int scrolledY = - getDecoratedTop(firstChild);
        for (int i = 0; i < firstChildPosition; i++) {
            Integer size = childSizesMap.get(i);
            scrolledY += size != null ? size : 0;
        }
        return scrolledY + getPaddingTop();
    }

    private int calcItemPosition(Operator operator) {
        if (rv == null) return RecyclerView.NO_POSITION;
        boolean vertical = getOrientation() == RecyclerView.VERTICAL;
        int length = vertical ? rv.getHeight() : rv.getWidth();
        int paddingStart = vertical ? rv.getPaddingTop() : rv.getPaddingStart();
        int paddingEnd = vertical ? rv.getPaddingBottom() : rv.getPaddingEnd();
        View item = null;
        for (int i = 0; i < rv.getChildCount(); i++) {
            item = operator.apply(vertical, paddingStart, paddingEnd, length, rv.getChildAt(i), item);
        }
        if (item == null) return RecyclerView.NO_POSITION;
        return getPosition(item);
    }

    private interface Operator {
        View apply(boolean vertical,int paddingStart, int paddingEnd, int length, View v1, View v2);
    }

    @Override
    public int findFirstVisibleItemPosition() {
        return findFirstVisibleItemPosition(false);
    }

    public int findFirstVisibleItemPosition(boolean ignorePadding) {
        return calcItemPosition((vertical, paddingStart, paddingEnd, length, v1, v2) -> {
            int actuallyLength = ignorePadding ? 0 : paddingStart;
            float v1Position = v1 == null ? Float.MAX_VALUE : (vertical ? v1.getY() + v1.getHeight() : v1.getX() + v1.getWidth());
            float v2Position = v2 == null ? Float.MAX_VALUE : (vertical ? v2.getY() + v2.getHeight() : v2.getX() + v2.getWidth());
            v1Position = v1Position < actuallyLength ? Float.MAX_VALUE : v1Position;
            v2Position = v2Position < actuallyLength ? Float.MAX_VALUE : v2Position;
            return v1Position < v2Position ? v1 : v2;
        });
    }

    @Override
    public int findFirstCompletelyVisibleItemPosition() {
        return findFirstCompletelyVisibleItemPosition(false);
    }

    public int findFirstCompletelyVisibleItemPosition(boolean ignorePadding) {
        return calcItemPosition((vertical, paddingStart, paddingEnd, length, v1, v2) -> {
            int actuallyLength = ignorePadding ? 0 : paddingStart;
            float v1Position = v1 == null ? Float.MAX_VALUE : (vertical ? v1.getY() : v1.getX());
            float v2Position = v2 == null ? Float.MAX_VALUE : (vertical ? v2.getY() : v2.getX());
            v1Position = v1Position < actuallyLength ? Float.MAX_VALUE : v1Position;
            v2Position = v2Position < actuallyLength ? Float.MAX_VALUE : v2Position;
            return v1Position < v2Position ? v1 : v2;
        });
    }

    @Override
    public int findLastVisibleItemPosition() {
        return findLastVisibleItemPosition(false);
    }

    public int findLastVisibleItemPosition(boolean ignorePadding) {
        return calcItemPosition((vertical, paddingStart, paddingEnd, length, v1, v2) -> {
            int actuallyLength = ignorePadding ? length : length - paddingEnd;
            float v1Position = v1 == null ? Float.MIN_VALUE : (vertical ? v1.getY() : v1.getX());
            float v2Position = v2 == null ? Float.MIN_VALUE : (vertical ? v2.getY() : v2.getX());
            v1Position = v1Position > actuallyLength ? Float.MIN_VALUE : v1Position;
            v2Position = v2Position > actuallyLength ? Float.MIN_VALUE : v2Position;
            return v1Position > v2Position ? v1 : v2;
        });
    }

    @Override
    public int findLastCompletelyVisibleItemPosition() {
        return findLastCompletelyVisibleItemPosition(false);
    }

    public int findLastCompletelyVisibleItemPosition(boolean ignorePadding) {
        return calcItemPosition((vertical, paddingStart, paddingEnd, length, v1, v2) -> {
            int actuallyLength = ignorePadding ? length : length - paddingEnd;
            float v1Position = v1 == null ? Float.MIN_VALUE : (vertical ? v1.getY() + v1.getHeight() : v1.getX() + v1.getWidth());
            float v2Position = v2 == null ? Float.MIN_VALUE : (vertical ? v2.getY() + v2.getHeight() : v2.getX() + v2.getWidth());
            v1Position = v1Position > actuallyLength ? Float.MIN_VALUE : v1Position;
            v2Position = v2Position > actuallyLength ? Float.MIN_VALUE : v2Position;
            return v1Position > v2Position ? v1 : v2;
        });
    }
}