Android RecyclerView（瀑布流）水平/垂直方向分割线

Android RecyclerView不像过去的ListView那样随意的设置水平方向的分割线，如果要实现RecyclerView的水平/垂直分割线，则需要继承自RecyclerView.ItemDecoration重写getItemOffsets方法，从而增加水平/垂直分割线。
写一个例子。
MainActivity.java：

package zhangphil.app;

import android.content.Context;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RecyclerView mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);

        // 两列
        int spanCount = 2;

        // StaggeredGridLayoutManager管理RecyclerView的布局。
        StaggeredGridLayoutManager mLayoutManager = new StaggeredGridLayoutManager(spanCount, StaggeredGridLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(mLayoutManager);

        //为RecyclerView增加分割线，水平和垂直方向都有。增加分割线值比如为32。
        RecyclerViewItemDecoration decoration = new RecyclerViewItemDecoration(32);
        mRecyclerView.addItemDecoration(decoration);

        RecyclerViewAdapter mAdapter = new RecyclerViewAdapter(this);
        mRecyclerView.setAdapter(mAdapter);
    }

    private class ItemViewHolder extends RecyclerView.ViewHolder {
        private TextView text;

        public ItemViewHolder(View itemView) {
            super(itemView);
            text = (TextView) itemView.findViewById(android.R.id.text1);
            text.setTextColor(Color.WHITE);
        }
    }

    public class RecyclerViewAdapter extends RecyclerView.Adapter<ItemViewHolder> {
        private Context context;

        public RecyclerViewAdapter(Context context) {
            super();
            this.context = context;
        }

        @Override
        public ItemViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
            View view = View.inflate(context, android.R.layout.simple_list_item_1, null);
            view.setBackgroundColor(Color.RED);
            ItemViewHolder holder = new ItemViewHolder(view);
            return holder;
        }

        @Override
        public void onBindViewHolder(ItemViewHolder viewHolder, int pos) {
            viewHolder.text.setText(String.valueOf(pos));
        }

        @Override
        public int getItemCount() {
            return 15;
        }
    }
}

布局文件，很简单，就放一个RecyclerView，注意背景颜色的设置：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/holo_orange_light">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v7.widget.RecyclerView>

</RelativeLayout>

最关键的RecyclerViewItemDecoration.java：

package zhangphil.app;

/**
 * Created by Phil on 2016/10/8.
 */

import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * 为RecyclerView增加间距
 * 预设2列，如果是3列，则左右值不同
 */
public class RecyclerViewItemDecoration extends RecyclerView.ItemDecoration {
    private int space = 0;
    private int pos;

    public RecyclerViewItemDecoration(int space) {
        this.space = space;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

        outRect.top = space;

        //该View在整个RecyclerView中位置。
        pos = parent.getChildAdapterPosition(view);

        //取模

        //两列的左边一列
        if (pos % 2 == 0) {
            outRect.left = space;
            outRect.right = space / 2;
        }

        //两列的右边一列
        if (pos % 2 == 1) {
            outRect.left = space / 2;
            outRect.right = space;
        }
    }
}

代码运行结果：