[转] 原文
自定义RecyclerView.ItemDecoration,实现RecyclerView的分割线效果
1.背景
RecyclerView是谷歌V7包下新增的控件,用来替代ListView和GridView使用的一个控件。在使用的过程中,往往需要使用到divider的效果(item之间的分割线)。而RecyclerView并不像ListView一样自带有divider的属性。而是需要用到RecyclerView.ItemDecoration这样一个类,但是ItemDecoration是一个抽象类,而且android内部并没有给它做一些效果的实现。那么就需要我们自己去继承并实现其中的方法,本文讲述的就是在GridLayoutManager和LinearLayoutManager下如何去实现ItemDecoration。至于RecyclerView.ItemDecoration的具体分析,大家可以去看看这篇文章http://blog.piasy.com/2016/03/26/Insight-Android-RecyclerView-ItemDecoration/ 这里不作过多的阐述。
2.实现基本的Item的divider
2.1 创建SpacesItemDecoration
创建一个类SpacesItemDecoration继承与RecyclerView.ItemDecoration,实现其中的onDraw和getItemOffsets方法,在这里我们的设计是左右距离相等,上下距离相等。
public class SpacesItemDecoration extends RecyclerView.ItemDecoration { private int leftRight; private int topBottom; public SpacesItemDecoration(int leftRight, int topBottom) { this.leftRight = leftRight; this.topBottom = topBottom; } @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { super.onDraw(c, parent, state); } @Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { } }
在这里我们主要实现的方法是onDraw和getItemOffsets,getItemOffsets重要确定divider的范围,而onDraw是对divider的具体实现。
2.2 LinearLayoutManager下divider的实现
首先在getItemOffsets方法中需要判断当前的RecyclerView所采用的哪种LayoutManager。这里要注意的是GridLayoutManager是继承LinearLayoutManager的,所以需要先判断是否为GridLayoutManager。
private SpacesItemDecorationEntrust getEntrust(RecyclerView.LayoutManager manager) { SpacesItemDecorationEntrust entrust = null; //要注意这边的GridLayoutManager是继承LinearLayoutManager,所以要先判断GridLayoutManager if (manager instanceof GridLayoutManager) { entrust = new GridEntrust(leftRight, topBottom, mColor); } else {//其他的都当做Linear来进行计算 entrust = new LinearEntrust(leftRight, topBottom, mColor); } return entrust; }
然后我们来看具体的实现,首先判断是VERTICAL还是HORIZONTAL。对于VERTICAL,每一个item必需的是top,left和right,但是最后一个item还需要bottom。而对于HORIZONTAL,每一个item必需的是top,left和bottom,但是最后一个item还需要right。
@Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager(); //竖直方向的 if (layoutManager.getOrientation() == LinearLayoutManager.VERTICAL) { //最后一项需要 bottom if (parent.getChildAdapterPosition(view) == layoutManager.getItemCount() - 1) { outRect.bottom = topBottom; } outRect.top = topBottom; outRect.left = leftRight; outRect.right = leftRight; } else { //最后一项需要right if (parent.getChildAdapterPosition(view) == layoutManager.getItemCount() - 1) { outRect.right = leftRight; } outRect.top = topBottom; outRect.left = leftRight; outRect.bottom = topBottom; } }
就这样,divider效果就实现了(当然是没有任何的颜色的)。调用方式只需要。
int leftRight = dip2px(7); int topBottom = dip2px(7); rv_content.addItemDecoration(new SpacesItemDecoration(leftRight, topBottom));
![](http://upload-images.jianshu.io/upload_images/2730072-31936cdb2c9638cb.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
![](http://upload-images.jianshu.io/upload_images/2730072-7d33ecab1b410057.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
2.3 GridLayoutManager下divider的实现
对于GridLayoutManager下的实现,相比LinearLayoutManager要复杂一些。首先当然是判断VERTICAL还是HORIZONTAL。对于VERTICAL,我们每一项必须的是top和left,但是对于最后一排的还需要bottom,同时对于最右侧的还需要right。根据这些,就很好写出它的一个规则了。同时HORIZONTAL下的也是类似的分析。
@Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager(); //判断总的数量是否可以整除 int totalCount = layoutManager.getItemCount(); int surplusCount = totalCount % layoutManager.getSpanCount(); int childPosition = parent.getChildAdapterPosition(view); if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) {//竖直方向的 if (surplusCount == 0 && childPosition > totalCount - layoutManager.getSpanCount() - 1) { //后面几项需要bottom outRect.bottom = topBottom; } else if (surplusCount != 0 && childPosition > totalCount - surplusCount - 1) { outRect.bottom = topBottom; } if ((childPosition + 1) % layoutManager.getSpanCount() == 0) {//被整除的需要右边 outRect.right = leftRight; } outRect.top = topBottom; outRect.left = leftRight; } else { if (surplusCount == 0 && childPosition > totalCount - layoutManager.getSpanCount() - 1) { //后面几项需要右边 outRect.right = leftRight; } else if (surplusCount != 0 && childPosition > totalCount - surplusCount - 1) { outRect.right = leftRight; } if ((childPosition + 1) % layoutManager.getSpanCount() == 0) {//被整除的需要下边 outRect.bottom = topBottom; } outRect.top = topBottom; outRect.left = leftRight; } }
这样,GridLayoutManager的效果就实现了,调用方法跟LinearLayoutManager下是一样的。效果如下
![](http://upload-images.jianshu.io/upload_images/2730072-6b887bd872d03650.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
![](http://upload-images.jianshu.io/upload_images/2730072-82b67ccfbcf4e61c.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
3.实现Item的带颜色分割线的效果
3.1 LinearManager下的实现
上述基本实现了item分割的效果,但是它没有办法设置颜色,颜色,颜色(重要的问题说三遍)。要实现颜色,首先我们得传入一个颜色色值。
//color的传入方式是resouce.getcolor protected Drawable mDivider; public SpacesItemDecorationEntrust(int leftRight, int topBottom, int mColor) { this.leftRight = leftRight; this.topBottom = topBottom; if (mColor != 0) { mDivider = new ColorDrawable(mColor); } }
有了颜色,那么我们就需要去重写onDraw方法了,我们需要去确定绘制的区域。先贴上代码
@Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager(); //没有子view或者没有没有颜色直接return if (mDivider == null || layoutManager.getChildCount() == 0) { return; } int left; int right; int top; int bottom; final int childCount = parent.getChildCount(); if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) { for (int i = 0; i < childCount - 1; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams(); //将有颜色的分割线处于中间位置 float center = (layoutManager.getTopDecorationHeight(child) - topBottom) / 2; //计算下边的 left = layoutManager.getLeftDecorationWidth(child); right = parent.getWidth() - layoutManager.getLeftDecorationWidth(child); top = (int) (child.getBottom() + params.bottomMargin + center); bottom = top + topBottom; mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } else { for (int i = 0; i < childCount - 1; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams(); //将有颜色的分割线处于中间位置 float center = (layoutManager.getLeftDecorationWidth(child) - leftRight) / 2; //计算右边的 left = (int) (child.getRight() + params.rightMargin + center); right = left + leftRight; top = layoutManager.getTopDecorationHeight(child); bottom = parent.getHeight() - layoutManager.getTopDecorationHeight(child); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } }
RecyclerView的机制是去绘制要显示在屏幕中的view,而没有显示出来的是不会去绘制。所以这边需要使用的是layoutManager.getChildCount()而不是layoutManager.getItemCount()。对于LinearManager下来说,需要绘制分割线的区域是两个item之间,这里分为VERTICAL和HORIZONTAL。我们拿VERTICAL来进行分析,首先获取item以及它的LayoutParams,在这里计算float center = (layoutManager.getTopDecorationHeight(child) - topBottom) / 2;
因为一个RecyclerView可以添加多个ItemDecoration,而且方法的调用顺序是先实现所有ItemDecoration的getItemOffsets方法,然后再去实现onDraw方法。目前没有找到办法去解决每个ItemDecoration的具体区域。所以退而求其次的将分割线绘制在所有ItemDecoration的中间区域(基本能满足一般的需求,当然可以自己修改位置满足自己的需求)。
然后我们要去确定绘制的区域,left就是所有ItemDecoration的宽度,right就是parent的宽度减去所有ItemDecoration的宽度。top是child的底部位置然后还要加上center(center的目的是绘制在中间区域),bottom就是top加上需要绘制的高度。同理在HORIZONTAL模式下可以类似的实现。使用一个ItemDecoration的效果
int leftRight = dip2px(2); int topBottom = dip2px(2); rv_content.addItemDecoration(new SpacesItemDecoration(leftRight, topBottom,getResources().getColor(R.color.colorPrimary)));
![](http://upload-images.jianshu.io/upload_images/2730072-41860f1a41f83f88.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
![](http://upload-images.jianshu.io/upload_images/2730072-01e589b05fc06f84.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
当然你也可以使用多个ItemDecoration
int leftRight = dip2px(10); int topBottom = dip2px(10); rv_content.addItemDecoration(new SpacesItemDecoration(leftRight, topBottom)); rv_content.addItemDecoration(new SpacesItemDecoration(dip2px(2), dip2px(2), getResources().getColor(R.color.colorPrimary)));
![](http://upload-images.jianshu.io/upload_images/2730072-87577a5fa0015b1a.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
![](http://upload-images.jianshu.io/upload_images/2730072-d9a4d92a39a4be3c.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
3.2 GridManager下的实现
GridManager下的实现的步骤类似与LinearManager,不同的是确定绘制分割线的区域。它的分割线的区域是相邻的item之间都需要有分割线。废话不多说,先上代码。
@Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager(); if (mDivider == null || layoutManager.getChildCount() == 0) { return; } //判断总的数量是否可以整除 int totalCount = layoutManager.getItemCount(); int surplusCount = totalCount % layoutManager.getSpanCount(); int left; int right; int top; int bottom; final int childCount = parent.getChildCount(); if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) { for (int i = 0; i < childCount; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams(); //得到它在总数里面的位置 final int position = parent.getChildAdapterPosition(child); //将带有颜色的分割线处于中间位置 final float centerLeft = (layoutManager.getLeftDecorationWidth(child) - leftRight) / 2; final float centerTop = (layoutManager.getTopDecorationHeight(child) - topBottom) / 2; //是否为最后一排 boolean isLast = surplusCount == 0 ? position > totalCount - layoutManager.getSpanCount() - 1 : position > totalCount - surplusCount - 1; //画下边的,最后一排不需要画 if ((position + 1) % layoutManager.getSpanCount() == 1 && !isLast) { //计算下边的 left = layoutManager.getLeftDecorationWidth(child); right = parent.getWidth() - layoutManager.getLeftDecorationWidth(child); top = (int) (child.getBottom() + params.bottomMargin + centerTop); bottom = top + topBottom; mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } //画右边的,能被整除的不需要右边,并且当数量不足的时候最后一项不需要右边 boolean first = totalCount > layoutManager.getSpanCount() && (position + 1) % layoutManager.getSpanCount() != 0; boolean second = totalCount < layoutManager.getSpanCount() && position + 1 != totalCount; if (first || second) { //计算右边的 left = (int) (child.getRight() + params.rightMargin + centerLeft); right = left + leftRight; top = child.getTop() + params.topMargin; //第一排的不需要上面那一丢丢 if (position > layoutManager.getSpanCount() - 1) { top -= centerTop; } bottom = child.getBottom() - params.bottomMargin; //最后一排的不需要最底下那一丢丢 if (!isLast) { bottom += centerTop; } mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } } else { for (int i = 0; i < childCount; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams(); //得到它在总数里面的位置 final int position = parent.getChildAdapterPosition(child); //将带有颜色的分割线处于中间位置 final float centerLeft = (layoutManager.getLeftDecorationWidth(child) - leftRight) / 2; final float centerTop = (layoutManager.getTopDecorationHeight(child) - topBottom) / 2; //是否为最后一排 boolean isLast = surplusCount == 0 ? position > totalCount - layoutManager.getSpanCount() - 1 : position > totalCount - surplusCount - 1; //画右边的,最后一排不需要画 if ((position + 1) % layoutManager.getSpanCount() == 1 && !isLast) { //计算右边的 left = (int) (child.getRight() + params.rightMargin + centerLeft); right = left + leftRight; top = layoutManager.getTopDecorationHeight(child); bottom = parent.getHeight() - layoutManager.getTopDecorationHeight(child); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } boolean first = totalCount > layoutManager.getSpanCount() && (position + 1) % layoutManager.getSpanCount() != 0; boolean second = totalCount < layoutManager.getSpanCount() && position + 1 != totalCount; //画下边的,能被整除的不需要下边 if (first || second) { left = child.getLeft() + params.leftMargin; if (position > layoutManager.getSpanCount() - 1) { left -= centerLeft; } right = child.getRight() - params.rightMargin; if (!isLast) { right += centerLeft; } top = (int) (child.getBottom() + params.bottomMargin + centerTop); bottom = top + topBottom; mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } } }
我们就VERTICAL的情况下来进行分析,首先横向的分割线,只需要在最左侧的item绘制出来的时候进行分割线的绘制就行了。当然最后一排是不需要的。
if ((position + 1) % layoutManager.getSpanCount() == 1 && !isLast) { //计算下边的 left = layoutManager.getLeftDecorationWidth(child); right = parent.getWidth() - layoutManager.getLeftDecorationWidth(child); top = (int) (child.getBottom() + params.bottomMargin + centerTop); bottom = top + topBottom; mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); }
水平的分割线的计算方式类似与LinearLayoutManager下的计算方式。这里不过多阐述。而竖直方向的会有一些区别。由于GridLayoutManager下,item的数量不一定能够刚好整除每排的数量。所以这边的绘制区域是根据每个item来进行确定的。
能被整除的或者当数量不足的时候最后一项不需要竖直的分割线。同时要注意补齐centerTop(分割线绘制在中间区域的位置)。
//画右边的,能被整除的不需要右边,并且当数量不足的时候最后一项不需要右边 boolean first = totalCount > layoutManager.getSpanCount() && (position + 1) % layoutManager.getSpanCount() != 0; boolean second = totalCount < layoutManager.getSpanCount() && position + 1 != totalCount; if (first || second) { //计算右边的 left = (int) (child.getRight() + params.rightMargin + centerLeft); right = left + leftRight; top = child.getTop() + params.topMargin; //第一排的不需要上面那一丢丢 if (position > layoutManager.getSpanCount() - 1) { top -= centerTop; } bottom = child.getBottom() - params.bottomMargin; //最后一排的不需要最底下那一丢丢 if (!isLast) { bottom += centerTop; } mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); }
HORIZONTAL下的情况可以进行类似的分析,代码的调用方式跟LinearLayoutManager下是一样的。
![](http://upload-images.jianshu.io/upload_images/2730072-522f02d409ebf707.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
![](http://upload-images.jianshu.io/upload_images/2730072-ce8704d79792326b.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)
4 最后
至此,RecyclerView的divider效果已经基本实现了。当然,你可以在这基础上进行修改,满足自己的一些需求。欢迎大家一起相互交流。代码已经上传至github https://github.com/hzl123456/SpacesItemDecoration
(ps:在实际的使用过程中,当对RecyclerView的item进行增加和删除的操作是,会使ItemDecoration的分割区域计算错误。原因是在添加和删除操作的时候,只会计算更新的部分区域的OutRect,导致出现问题,这个时候我们只需要在添加和删除操作之后调用RecyclerView的invalidateItemDecorations()方法就可以解决问题了)