RecycleView 分割线设置及监听滚动状态

一、RecycleView 分割线

ListView中的分割线可以通过属性divider和dividerHeight分别设置颜色值/图片及分割线高度。而RecycleView并没有提供这两个属性设置分割线。
作为ListView的升级版列表控件，当然也是支持分割线的设置的。RecycleView分割线需要通过addItemDecoration(ItemDecoration decor)设置;

ItemDecoration有3个方法，ItemDecoration并没有对其实现，需要我们自己实现自定义的分割线；
onDraw：其绘制将会在每个Item被绘制之前进行；
onDrawOver:在绘制完Item后进行绘制；
getItemOffsets:通过outRect.set()为每个item设置偏移量。

下面是网上提供的通用分割线实现类，可以根据自己不同需求做修改；

public class RecycleViewDivider extends RecyclerView.ItemDecoration {private Paint mPaint;private Drawable mDivider;private int mDividerHeight = 2;//分割线高度，默认为2pxprivate int mOrientation;//列表的方向：LinearLayoutManager.VERTICAL或LinearLayoutManager.HORIZONTALprivate 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*/public RecycleViewDivider(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，高度默认为图片原始高度*/public RecycleViewDivider(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 drawable    分割线图片，高度默认为图片原始高度*/public RecycleViewDivider(Context context, int orientation, Drawable drawable) {this(context, orientation);mDivider = drawable;mDividerHeight = mDivider.getIntrinsicHeight();}/*** 自定义分割线** @param context* @param orientation 列表方向* @param drawable    分割线图片* @param drawableHeight    分割线图片高度*/public RecycleViewDivider(Context context, int orientation, Drawable drawable, intdrawableHeight) {this(context, orientation);mDivider = drawable;mDividerHeight = drawableHeight;}/*** 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 RecycleViewDivider(Context context, int orientation, int dividerHeight, intdividerColor) {this(context, orientation);mDividerHeight = dividerHeight;mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setColor(dividerColor);mPaint.setStyle(Paint.Style.FILL);}//获取分割线尺寸@Overridepublic void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.Statestate) {super.getItemOffsets(outRect, view, parent, state);outRect.set(0, 0, 0, mDividerHeight);}//绘制分割线@Overridepublic void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {super.onDraw(c, parent, 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();final int right = parent.getMeasuredWidth() - parent.getPaddingRight();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 top = child.getBottom() + layoutParams.bottomMargin;final int bottom = top + mDividerHeight;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();final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom();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 + mDividerHeight;if (mDivider != null) {mDivider.setBounds(left, top, right, bottom);mDivider.draw(canvas);}if (mPaint != null) {canvas.drawRect(left, top, right, bottom, mPaint);}}}
}

这里设置横向图片分割线，分割线的高度默认为图片高度；

 mRecyclerView.addItemDecoration(new RecycleViewDivider(this, LinearLayoutManager.HORIZONTAL, R.mipmap.divier_img));

二、RecycleView 监听滚动状态、及顶部/末尾位置

还记得ListView是如何监听滚动到顶部或末尾的吗？通过设置setOnScrollListener实现的；

mListView.setOnScrollListener(new AbsListView.OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {// TODO Auto-generated method stubif (scrollState==OnScrollListener.SCROLL_STATE_IDLE) {// 滚动停止}else if (scrollState==OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {// 手指滚动状态}else if (scrollState==OnScrollListener.SCROLL_STATE_FLING) {// 手指不动了，但是屏幕还在滚动状态,靠惯性滚动}}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {// TODO Auto-generated method stubif (firstVisibleItem==0) {// 滚动到顶部}else if (firstVisibleItem+visibleItemCount>= totalItemCount) {// 滚动到尾部}}
});

在RecycleView中，可以通过线性布局对象LinearLayoutManager监听顶部/尾部位置；
其提供以下方法（主要区别是item是否完全显示，还是存在一半被遮挡）；
findFirstVisibleItemPosition() ：第一个显示的item位置；
findFirstCompletelyVisibleItemPosition() ：第一个完全显示的item位置；
findLastVisibleItemPosition() ：最后一个显示的item位置；
findLastCompletelyVisibleItemPosition()：最后一个完全显示的item位置。

接着设置滚动监听setonScrollListener，然后对第一个显示的item位置和末尾显示的item位置判断是否滚动到屏幕开始/末尾。

mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {@Overridepublic void onScrolled(RecyclerView recyclerView, int dx, int dy) {// TODO Auto-generated method stubif (!(mLayoutManager instanceof LinearLayoutManager)) {Toast.makeText(MainActivity.this, "不是线性的布局结构", Toast.LENGTH_SHORT).show();return;}LinearLayoutManager linearLayoutManager = (LinearLayoutManager) mLayoutManager;if (linearLayoutManager.findFirstCompletelyVisibleItemPosition() == 0) {Toast.makeText(MainActivity.this, "滚动到顶部", Toast.LENGTH_SHORT).show();}if (linearLayoutManager.findLastCompletelyVisibleItemPosition() == mRecyclerView.getAdapter().getItemCount() - 1) {Toast.makeText(MainActivity.this, "滚动到尾部", Toast.LENGTH_SHORT).show();}}@Overridepublic void onScrollStateChanged(RecyclerView recyclerView, int newState) {// TODO Auto-generated method stubif (newState==RecyclerView.SCROLL_STATE_IDLE){Toast.makeText(MainActivity.this, "滚动停止", Toast.LENGTH_SHORT).show();}else if (newState == RecyclerView.SCROLL_STATE_DRAGGING){Toast.makeText(MainActivity.this, "手指拖动", Toast.LENGTH_SHORT).show();}else if (newState==RecyclerView.SCROLL_STATE_SETTLING){Toast.makeText(MainActivity.this, "手指离开屏幕，滑动", Toast.LENGTH_SHORT).show();}}});