上面写了一篇自定义分割线，重在理解分割线的绘制原理，这篇侧重于项目实战中应用。

1.创建继承ItemDecoration

构造创建，这次使用attrs 的方式

 private Drawable mDivider;
  private int[] attrs = new int[]{
        android.R.attr.listDivider
   };
public DividerGridItemDecoration(Context context) {
    TypedArray typedArray = context.obtainStyledAttributes(attrs);
    mDivider = typedArray.getDrawable(0);
    typedArray.recycle();
}

在清单文件中配置主题

   <activity android:name=".fenline.RecyclerViewActivity"
        android:theme="@style/AppTheme"/>

在主题中配置listDivider属性

 <!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="android:listDivider">@drawable/list_item_divider</item>
</style>

然而list_item_divider自己绘制的分割线样式，举个例子：

 <?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
<size android:height="0.5dp"
    android:width="0.5dp"
    />
 <solid android:color="@color/login_color" />
</shape>

2.onDraw方法区分逻辑

onDraw方法区分是水平还是竖直分割线

   @Override
   public void onDraw(Canvas c, RecyclerView parent, State state) {
    drawVertical(c, parent);
    drawHorizontal(c, parent);
   }

绘制竖直分割线方法

private void drawVertical(Canvas c, RecyclerView parent) {
    //绘制垂直间隔线(垂直的矩形)
    int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        View child = parent.getChildAt(i);
        RecyclerView.LayoutParams params = (LayoutParams) child.getLayoutParams();
        int left = child.getRight() + params.rightMargin;
        int right = left + mDivider.getIntrinsicWidth();
        int top = child.getTop() - params.topMargin;
        int bottom = child.getBottom() + params.bottomMargin;
        mDivider.setBounds(left, top, right, bottom);
        mDivider.draw(c);
    }
}

绘制水平分割线方法

  private void drawHorizontal(Canvas c, RecyclerView parent) {
    // 绘制水平间隔线
    int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        View child = parent.getChildAt(i);
        RecyclerView.LayoutParams params = (LayoutParams) child.getLayoutParams();
        int left = child.getLeft() - params.leftMargin;
        int right = child.getRight() + params.rightMargin + mDivider.getIntrinsicWidth();
        int top = child.getBottom() + params.bottomMargin;
        int bottom = top + mDivider.getIntrinsicHeight();
        mDivider.setBounds(left, top, right, bottom);
        mDivider.draw(c);
    }
}

3.getItemOffsets逻辑实现

  @Override
   public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
    // 四个方向的偏移值
    int right = mDivider.getIntrinsicWidth();
    int bottom = mDivider.getIntrinsicHeight();

    int position = ((LayoutParams) view.getLayoutParams()).getViewLayoutPosition();

    if (isLastColumn(position, parent)) {// 是否是最后一列
        right = 0;
    }
    if (isLastRow(position, parent)) {// 是否是最后一行
        bottom = 0;
    }
    outRect.set(0, 0, right, bottom);
}

其他方法

 /**
 * 是否是最后一列
 */
public boolean isLastColumn(int itemPosition, RecyclerView parent) {
    int spanCount = getSpanCount(parent);
    if ((itemPosition + 1) % spanCount == 0) {
        return true;
    } else {
        return false;
    }
}

/**
 * 是否是最后一行
 */
public boolean isLastRow(int itemPosition, RecyclerView parent) {

    int spanCount = getSpanCount(parent);

    int childCount = parent.getAdapter().getItemCount();

    int rowNumber = childCount % spanCount == 0 ? childCount / spanCount : (childCount / spanCount) + 1;

    if (itemPosition > ((rowNumber - 1) * spanCount - 1)) {
        return true;
    }

    return false;
}

/**
 * 获取一行有多少列
 */
public int getSpanCount(RecyclerView parent) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();

    if (layoutManager instanceof GridLayoutManager) {
        // 获取一行的spanCount
        GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
        int spanCount = gridLayoutManager.getSpanCount();
        return spanCount;
    }
    return 1;
}

4.使用

使用方法很简单，只需添加如下这句：

   mRecyclerView.addItemDecoration(new DividerGridItemDecoration(this));