public class 初一LayoutManager extends RecyclerView.LayoutManager {

    @Override
    public RecyclerView.LayoutParams generateDefaultLayoutParams() {
        return new RecyclerView.LayoutParams(
                RecyclerView.LayoutParams.WRAP_CONTENT,
                RecyclerView.LayoutParams.WRAP_CONTENT);
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
        try {
            super.onLayoutChildren(recycler, state);

            //分离和废弃附加的视图
            detachAndScrapAttachedViews(recycler);
            //获取屏幕宽度
            int sumWidth = getWidth();


            //recyclerview行宽
            int curLineWidth = 0；
            //recyclerview行高
            int  curLineTop = 0;
            //最后一个item的最大可行高度
            int lastLineMaxHeight = 0;
            for (int i = 0; i < getItemCount(); i++) {
                //获取第i 个位置的item的view
                View view = recycler.getViewForPosition(i);
                //添加这个item到recyclerview中
                addView(view);
                //获取添加了item后的recyclerview
                measureChildWithMargins(view, 0, 0)
               //获取添加了item后recyclerview的宽度;
                int width = getDecoratedMeasuredWidth(view);
              //获取添加了item后recyclerview的宽度;
                int height = getDecoratedMeasuredHeight(view);
              //recyclerview行宽+item.getWidth
                curLineWidth += width;
                if (curLineWidth <= sumWidth) {
                    //不需要换行
                    layoutDecorated(view, curLineWidth - width, curLineTop, curLineWidth, curLineTop + height);
                    //比较当前行多有item的最大高度
                    lastLineMaxHeight = Math.max(lastLineMaxHeight, height);
                } else {
                    //换行
                    curLineWidth = width;
                    if (lastLineMaxHeight == 0) {
                        lastLineMaxHeight = height;
                    }
                    //记录当前行top
                    curLineTop += lastLineMaxHeight;

                    layoutDecorated(view, 0, curLineTop, width, curLineTop + height);
                    lastLineMaxHeight = height;
                }
            }
        } catch (IndexOutOfBoundsException e) {
            
        }

    }

}