RecyclerView 添加分割线

RecyclerView 由于其灵活性已经被越来越多的人使用，但是其本身是没有分割线效果的。
一般有两种解决办法：
1、根据需要给item条目设置margin或者padding值。
2、用itemdecoration绘制分割线。
主要说说第二种方法。
分割线需要继承 RecyclerView.ItemDecoration类，并自己实现其中的方法。
① 线性布局的分割线：
效果图：

DividerItemDecoration.class 代码如下：

private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
// 线性列表 方向
public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;
public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;
private Drawable mDivider;
private int mOrientation;
private Paint mPaint;
private int mDividerHeight = 2;

/** * 默认样式分割线 
* 宽度为2 颜色为灰色 
* 
* @param context
 * @param orientation
 */
public DividerItemDecoration(Context context, int orientation) {   
   final TypedArray a = context.obtainStyledAttributes(ATTRS);   
   mDivider = a.getDrawable(0);   
   a.recycle();    
   setOrientation(orientation);
}
/** 
* 自定义分割线 
* 
* @param context
* @param orientation 列表方向
* @param drawableId  分割线图片 
*/
public DividerItemDecoration(Context context, int orientation, int drawableId) {    
    this(context, orientation);    
    mDivider = ContextCompat.getDrawable(context, drawableId);    
    mDividerHeight = mDivider.getIntrinsicHeight();
}
/** * 自定义分割线 
*
* @param context 
* @param orientation   列表方向 
* @param dividerHeight 分割线高度
* @param dividerColor  分割线颜色 
*/
public DividerItemDecoration(Context context, int orientation, int dividerHeight, int dividerColor) {    
    this(context, orientation);    
    mDividerHeight = dividerHeight;    
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);   
    mPaint.setColor(context.getResources().getColor(dividerColor));    
    mPaint.setStyle(Paint.Style.FILL);
}

public void setOrientation(int orientation) {   
    if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {        
         throw new IllegalArgumentException("invalid orientation");    
    }    
    mOrientation = orientation;
}

@Override
public void onDraw(Canvas c, RecyclerView parent) {    
    LogUtil.d("onDraw()");   
    if (mOrientation == VERTICAL_LIST) {        
        drawVertical(c, parent);    
    } else { 
       drawHorizontal(c, parent);    
    }
}

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

// 绘制垂直排列的分割线
public void drawVertical(Canvas c, RecyclerView parent) {
    final int left = parent.getPaddingLeft();
    final int right = parent.getWidth() - parent.getPaddingRight();
    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        RecyclerView v = new RecyclerView(parent.getContext());
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child                .getLayoutParams();
        final int top = child.getBottom() + params.bottomMargin;
        final int bottom = top + mDividerHeight;
        if (mDivider != null) {
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
        if (mPaint != null) {
            c.drawRect(left, top, right, bottom, mPaint);
        }
    }
}

// 绘制水平排列的分割线
public void drawHorizontal(Canvas c, RecyclerView parent) {
    final int top = parent.getPaddingTop();
    final int bottom = parent.getHeight() - parent.getPaddingBottom();
    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child                .getLayoutParams();
        final int left = child.getRight() + params.rightMargin;
        final int right = left + mDividerHeight;
        if (mDivider != null) {
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
        if (mPaint != null) {
            c.drawRect(left, top, right, bottom, mPaint);
        }
    }
}

@Override
public void getItemOffsets(Rect outRect, int itemPosition,RecyclerView parent) {
    if (mOrientation == VERTICAL_LIST) {
        outRect.set(0, 0, 0, mDividerHeight);
    } else {
        outRect.set(0, 0, mDividerHeight, 0);
    }
}

②网格布局的分割线
效果图：

private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
private Drawable mDivider;
private Paint mPaint;
private int mDividerHeight = 2;

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

/** * 自定义分割线
 *
 * @param context
 * @param drawableId 分割线图片
 */
public DividerGridItemDecoration(Context context, int drawableId) {
    mDivider = ContextCompat.getDrawable(context, drawableId);
    mDividerHeight = mDivider.getIntrinsicHeight();
}

/** * 自定义分割线
 *
 * @param context
 * @param dividerHeight 分割线高度
 * @param dividerColor  分割线颜色
 */
public DividerGridItemDecoration(Context context, int dividerHeight, int dividerColor) {
    mDividerHeight = dividerHeight;
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setColor(context.getResources().getColor(dividerColor));
    mPaint.setStyle(Paint.Style.FILL);
}

@Override
public void onDraw(Canvas c, RecyclerView parent, State state) {
    drawHorizontal(c, parent);
    drawVertical(c, parent);
}
private int getSpanCount(RecyclerView parent) {
    // 列数
    int spanCount = -1;
    LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        spanCount = ((StaggeredGridLayoutManager) layoutManager).getSpanCount();
    }
    return spanCount;
}

// 绘制水平线
public void drawHorizontal(Canvas c, RecyclerView parent) {
    int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
        final int left = child.getLeft() - params.leftMargin;
        final int right = child.getRight() + params.rightMargin+ mDividerHeight;
        final int top = child.getBottom() + params.bottomMargin;
        final int bottom = top + mDividerHeight;
        if (mDivider != null) {
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
        if (mPaint != null) {
            c.drawRect(left, top, right, bottom, mPaint);
        }
    }
}

// 绘制垂直线
public void drawVertical(Canvas c, RecyclerView parent) {
    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
        final int top = child.getTop() - params.topMargin;
        final int bottom = child.getBottom() + params.bottomMargin;
        final int left = child.getRight() + params.rightMargin;
        final int right = left + mDividerHeight;
        if (mDivider != null) {
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
        if (mPaint != null) {
            c.drawRect(left, top, right, bottom, mPaint);
        }
    }
}

// 判断是否是最后一列
private boolean isLastColum(RecyclerView parent, int pos, int spanCount, int childCount) {
    LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if ((pos + 1) % spanCount == 0)// 如果是最后一列，则不需要绘制右边
        {
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager).getOrientation();
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            if ((pos + 1) % spanCount == 0) {
                // 如果是最后一列，则不需要绘制右边
                return true;
            }
        } else {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最后一列，则不需要绘制右边
                return true;
        }
    }
    return false;
}

// 判断是否是最后一行
private boolean isLastRaw(RecyclerView parent, int pos, int spanCount, int childCount) {
        LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最后一行，则不需要绘制底部
                return true;
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager).getOrientation();
            // StaggeredGridLayoutManager 且纵向滚动
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                childCount = childCount - childCount % spanCount;
                // 如果是最后一行，则不需要绘制底部
                if (pos >= childCount)
                    return true;
            } else
            // StaggeredGridLayoutManager 且横向滚动
            {
                // 如果是最后一行，则不需要绘制底部
                if ((pos + 1) % spanCount == 0) {
                    return true;
                }
            }
        }
        return false;
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition,RecyclerView parent) {
        int spanCount = getSpanCount(parent);
        int childCount = parent.getAdapter().getItemCount();
        if (isLastRaw(parent, itemPosition, spanCount, childCount))// 如果是最后一行，则不需要绘制底部
        {
            outRect.set(0, 0, mDividerHeight, 0);
        } else if (isLastColum(parent, itemPosition, spanCount, childCount))// 如果是最后一列，则不需要绘制右边
        {
            outRect.set(0, 0, 0, mDividerHeight);
        } else {
            outRect.set(0, 0, mDividerHeight, mDividerHeight);
        }
    }
}

参考资料：鸿洋大神的博客：http://blog.csdn.net/lmj623565791/article/details/45059587 。