首先自定义一个RecyclerViewDivider 继承 RecyclerView.ItemDecoration，实现自定义。

public class RecyclerViewDivider extends RecyclerView.ItemDecoration {
private Paint mPaint;
private Drawable mDivider;
private int mDividerSize = 2;//分割线高度，默认为1px
private int mOffsetStart = 0;
private int mOffsetEnd = 0;
private int mOrientation;//列表的方向：LinearLayoutManager.VERTICAL或LinearLayoutManager.HORIZONTAL
private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

/**
* 默认分割线：高度为2px，颜色为灰色
*
* @param context
* @param orientation 列表方向
*/
private RecyclerViewDivider(Context context, int orientation) {
if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
throw new IllegalArgumentException("请输入正确的参数！");
}
mOrientation = orientation;

final TypedArray a = context.obtainStyledAttributes(ATTRS);
mDivider = a.getDrawable(0);
a.recycle();
}

/**
* 自定义分割线
*
* @param context
* @param orientation 列表方向
* @param drawableId 分割线图片
*/
public RecyclerViewDivider(Context context, int orientation, int drawableId) {
this(context, orientation);
mDivider = ContextCompat.getDrawable(context, drawableId);
mDividerSize = mDivider.getIntrinsicHeight();
}

/**
* 自定义分割线
*
* @param context
* @param orientation 列表方向
* @param dividerSize 分割线高度
* @param dividerColor 分割线颜色
*/
public RecyclerViewDivider(Context context, int orientation, int dividerSize, @ColorRes int dividerColor) {
this(context, orientation);
mDividerSize = dividerSize;
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

mPaint.setColor(context.getResources().getColor(dividerColor));
mPaint.setStyle(Paint.Style.FILL);
}

/**
* 自定义分割线
*
* @param context context
* @param orientation 列表方向
* @param dividerHeight 分割线高度
* @param dividerColor 分割线颜色
* @param offsetStart 起始偏移量
* @param offsetEnd 结束偏移量
*/
public RecyclerViewDivider(Context context, int orientation, int dividerHeight, @ColorRes int dividerColor, int offsetStart, int offsetEnd) {
this(context, orientation);
mDividerSize = dividerHeight;
mOffsetStart = Util.dp2px(context, offsetStart);
mOffsetEnd = Util.dp2px(context, offsetEnd);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
if (dividerColor == 0) {
dividerColor = R.color.lightGray;
}
mPaint.setColor(context.getResources().getColor(dividerColor));
mPaint.setStyle(Paint.Style.FILL);
}

//重写此方法，防止设置的波纹背景把分隔线覆盖掉。
@Override
public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
RecyclerView.ViewHolder childViewHolder = parent.getChildViewHolder(view);
if (childViewHolder.getItemViewType() != 0) {
outRect.set(0, 0, 0, 0);
return;
}
if (mOrientation == LinearLayoutManager.HORIZONTAL) {
outRect.set(0, 0, 0, mDividerSize);
} else {
outRect.set(0, 0, mDividerSize, 0);
}
}

//绘制分割线
@Override
public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
if (mOrientation == LinearLayoutManager.VERTICAL) {
drawVertical(c, parent);
} else {
drawHorizontal(c, parent);
}
}

//绘制横向 item 分割线
private void drawHorizontal(Canvas canvas, RecyclerView parent) {
final int left = parent.getPaddingLeft() + mOffsetStart;
final int right = parent.getMeasuredWidth() - (parent.getPaddingRight() + mOffsetEnd);
final int childSize = parent.getChildCount();
for (int i = 0; i < childSize - 1; i++) {
final View child = parent.getChildAt(http://www.my516.com);

RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int top = child.getBottom() + layoutParams.bottomMargin;
final int bottom = top + mDividerSize;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}

//绘制纵向 item 分割线
private void drawVertical(Canvas canvas, RecyclerView parent) {
final int top = parent.getPaddingTop() + mDividerSize;
final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom() + mDividerSize;
final int childSize = parent.getChildCount();
for (int i = 0; i < childSize; i++) {
final View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int left = child.getRight() + layoutParams.rightMargin;
final int right = left + mDividerSize;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}
}
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举个例子：

rcyDetailsDelegation.addItemDecoration(new RecyclerViewDivider(getContext(), LinearLayoutManager.HORIZONTAL,
5, R.color.white, 8, 8));
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其中提供一个 RecyclerViewDivider：
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