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：