精准计算RecyclerView滑动距离

最近遇到需求，要计算RecyclerView滑动距离，用提供的computeVerticalScrollOffset()方法得到的值不是很准确。是基于item的平均高度算得，如果列表中item高度一致可以用此方法。问题来了，我的应用场景是各item高度不一，这时就只能另找方法了。

简单粗暴，直接上代码：

public class OffSetLinearLayoutManager extends LinearLayoutManager {

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

private Map<Integer, Integer> heightMap = new HashMap<>();

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

public int computeVerticalScrollOffsetExact() {
    if (getChildCount() == 0) {
        return 0;
    }
    try {
        int firstVisiablePosition = findFirstVisibleItemPosition();
        if (firstVisiablePosition == -1) {
            return 0;
        }
        View firstVisiableView = findViewByPosition(firstVisiablePosition);
        int offsetY = -(int) (firstVisiableView.getY());
        for (int i = 0; i < firstVisiablePosition; i++) {
            offsetY += heightMap.get(i) == null ? 0 : heightMap.get(i);
        }
        return offsetY;
    } catch (Exception e) {
        return 0;
    }
}

}