android控件RecyclerView中，如何显示自定义分割线以及最后一项去除分割线

在控件RecyclerView中，分割线DividerItemDecoration类的使用经常见，如果是使用自带的分割线，只需要这样写即可

   RecyclerView mRecyclerView;
 mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));

会出现一条1pd的灰色的分割线，但是我如果想自己写自定义的分割线呢，这个时候需要我们自定义一个shape，在里面进行自定义样式然后进行引用

代码如下：divider.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="#CB8589" />
    <size android:height="15dp" />
</shape>

那我怎么在我的java里面用呢，代码如下：

        //添加自定义的分割线
      DividerItemDecoration divider = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
     divider.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
     mRecyclerView.addItemDecoration(divider);

如此，我的模拟器上就出现了又粗又红的分割线

但是这个时候又有问题，我每个子项都有，那么我如果想最后一个不要分割线呢，这个时候，我打开了DividerItemDecoration类的源码，发现了循环的地方

我只需要把这个地方减1，那么我不就可以删去最后一个子项的分割线了吗，显然，改源码是很不合理的，于是，我新建一个GridItemDecoration的类，修改如下：

GridItemDecoration.java

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.example.administrator.myapplication;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.RecyclerView.ItemDecoration;
import android.support.v7.widget.RecyclerView.State;
import android.util.Log;
import android.view.View;

public class GridItemDecoration extends ItemDecoration {
    public static final int HORIZONTAL = 0;
    public static final int VERTICAL = 1;
    private static final String TAG = "DividerItem";
    private static final int[] ATTRS = new int[]{16843284};
    private Drawable mDivider;
    private int mOrientation;
    private final Rect mBounds = new Rect();

    public GridItemDecoration(Context context, int orientation) {
        TypedArray a = context.obtainStyledAttributes(ATTRS);
        this.mDivider = a.getDrawable(0);
        if (this.mDivider == null) {
            Log.w("DividerItem", "@android:attr/listDivider was not set in the theme used for this DividerItemDecoration. Please set that attribute all call setDrawable()");
        }

        a.recycle();
        this.setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != 0 && orientation != 1) {
            throw new IllegalArgumentException("Invalid orientation. It should be either HORIZONTAL or VERTICAL");
        } else {
            this.mOrientation = orientation;
        }
    }

    public void setDrawable(@NonNull Drawable drawable) {
        if (drawable == null) {
            throw new IllegalArgumentException("Drawable cannot be null.");
        } else {
            this.mDivider = drawable;
        }
    }

    public void onDraw(Canvas c, RecyclerView parent, State state) {
        if (parent.getLayoutManager() != null && this.mDivider != null) {
            if (this.mOrientation == 1) {
                this.drawVertical(c, parent);
            } else {
                this.drawHorizontal(c, parent);
            }

        }
    }

    private void drawVertical(Canvas canvas, RecyclerView parent) {
        canvas.save();
        int left;
        int right;
        if (parent.getClipToPadding()) {
            left = parent.getPaddingLeft();
            right = parent.getWidth() - parent.getPaddingRight();
            canvas.clipRect(left, parent.getPaddingTop(), right, parent.getHeight() - parent.getPaddingBottom());
        } else {
            left = 0;
            right = parent.getWidth();
        }

        int childCount = parent.getChildCount();

        //当最后一个子项的时候去除下划线
        for (int i = 0; i < childCount - 1; ++i) {
            View child = parent.getChildAt(i);
            parent.getDecoratedBoundsWithMargins(child, this.mBounds);
            int bottom = this.mBounds.bottom + Math.round(child.getTranslationY());
            int top = bottom - this.mDivider.getIntrinsicHeight();
            this.mDivider.setBounds(left, top, right, bottom);
            this.mDivider.draw(canvas);
        }

        canvas.restore();
    }

    private void drawHorizontal(Canvas canvas, RecyclerView parent) {
        canvas.save();
        int top;
        int bottom;
        if (parent.getClipToPadding()) {
            top = parent.getPaddingTop();
            bottom = parent.getHeight() - parent.getPaddingBottom();
            canvas.clipRect(parent.getPaddingLeft(), top, parent.getWidth() - parent.getPaddingRight(), bottom);
        } else {
            top = 0;
            bottom = parent.getHeight();
        }

        int childCount = parent.getChildCount();

        for (int i = 0; i < childCount; ++i) {
            View child = parent.getChildAt(i);
            parent.getLayoutManager().getDecoratedBoundsWithMargins(child, this.mBounds);
            int right = this.mBounds.right + Math.round(child.getTranslationX());
            int left = right - this.mDivider.getIntrinsicWidth();
            this.mDivider.setBounds(left, top, right, bottom);
            this.mDivider.draw(canvas);
        }

        canvas.restore();
    }

    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
        if (this.mDivider == null) {
            outRect.set(0, 0, 0, 0);
        } else {
            if (this.mOrientation == 1) {
                outRect.set(0, 0, 0, this.mDivider.getIntrinsicHeight());
            } else {
                outRect.set(0, 0, this.mDivider.getIntrinsicWidth(), 0);
            }

        }
    }
}

如此，我在activity里面把这个类引进就可以：

  //最后一个不显示分割线且自定义分割线
        GridItemDecoration gridItemDecoration = new GridItemDecoration(this, DividerItemDecoration.VERTICAL);
        gridItemDecoration.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
        mRecyclerView.addItemDecoration(gridItemDecoration);

完整代码如下：

package com.example.administrator.myapplication;

import android.content.ContextWrapper;
import android.graphics.Paint;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.DividerItemDecoration;
import android.support.v7.widget.RecyclerView;

import java.util.List;
import java.util.ArrayList;

public class BodyActivity extends AppCompatActivity {
    RecyclerView mRecyclerView;
    public Paint paint;

    @Override
    protected void onCreate(Bundle saveInstanceState) {
        super.onCreate(saveInstanceState);
        setContentView(R.layout.activity_body);
        //1.获取控件
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //设置布局方式
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));//线性布局
//        mRecyclerView.setLayoutManager(new GridLayoutManager(this,2));//网格布局
        mRecyclerView.setHasFixedSize(true); //是否重新计算大小

        //3.准备数据
        List<News> newsList = new ArrayList<>();
        News news;
        for (int i = 1; i <= 20; i++) {
            news = new News();
            news.setNewsTitle("java是世界上最好的语言" + i);
            news.setNewsSource("新华网" + i);
            news.setPublishTime("2018-8-6");
            newsList.add(news);
        }

        //添加Android自带的分割线
//    mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));

        //添加自定义的分割线
//        DividerItemDecoration divider = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
//        divider.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
//        mRecyclerView.addItemDecoration(divider);

        //最后一个不显示分割线且自定义分割线
        GridItemDecoration gridItemDecoration = new GridItemDecoration(this, DividerItemDecoration.VERTICAL);
        gridItemDecoration.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
        mRecyclerView.addItemDecoration(gridItemDecoration);

        //4.准备适配器
        NewsAdapter newsAdapter = new NewsAdapter(newsList);
        mRecyclerView.setAdapter(newsAdapter);

    }
}