安卓RecyclerView灵活适配：带“头”的RecyclerView

项目小模块功能实现的差不多了，近几日在做体验，其中有个页面使用了RecyclerView，并设有头布局独占两格！！！

像这样

那么每个Item之间的空隙调节就回出现很大的问题，头布局两边距离屏幕的宽度显然和下边两列是不一样的当然，如果你还对头布局的设置存在一定问题，请参考：

https://blog.csdn.net/zxt0601/article/details/52267325

RecyclerView的万能适配器：https://www.cnblogs.com/liushilin/p/5720926.html（后续将给出详细的讲解），欢迎关注订阅博客https://blog.csdn.net/Sailor_luo

为RecyclerView添加Header和Footer：https://www.jianshu.com/p/991062d964cf

问题来了，到底如何适配这个页面呢？padding？margin？显然有点不太行

网上有一些解决方案是：

MyItemDecoration myItemDecoration = new MyItemDecoration(2, 60,true);

动态设置是对的，但是如何做到头和身体分开灵活控制呢？直接上工具吧！

import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.view.View;
public class MyItemDecoration extends RecyclerView.ItemDecoration {

        private int spanCount;
        private int spacing;
        private boolean includeEdge;

        /**
         * 从哪个位置开始设置间距，有的宫格视图有头视图
         */
        private int startFrom;

        public MyItemDecoration(int spanCount, int spacing, boolean includeEdge) {
            this.spanCount = spanCount;
            this.spacing = spacing;
            this.includeEdge = includeEdge;
        }

        /**
         * 设置从哪个位置开始设置间距
         *
         * @param position
         */
        public void setStartFrom(int position) {
            this.startFrom = position;
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            int position = parent.getChildAdapterPosition(view); // item position
            if (position < startFrom) {
                return;
            }

            // position - startFrom排除不考虑的位置这样算才正确
            position = position - startFrom;
            int column = position % spanCount; // item column

            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }
        }
    }

用法可想而知：

就调用他

public void setStartFrom(int position) {
            this.startFrom = position;
        }

问题解决！