一、需求
之前一篇博客使用ViewPager实现轮播图《》，但是ViewPager有个天生的缺陷是View无法重用，此外ViewPager的滑动过程会频繁requestLayout，尽管可以通过addViewInLayout和removeViewInLayout配合PagerAdapter 的startUpdate和finishUpdate可以减少重绘，但在ListView和RecyclerView中仍然达不到最好的效果。因此，使用一种新的方式十分必要。
二、代码实现
RecyclerPagerView
public class RecyclerPagerView extends RecyclerView implements Handler.Callback { private static final long TASK_TIMEOUT = 3000; public OnPageChangeListener onPageChangeListener; private final Handler mRecyclerHandler; private final int MSG_PLAY_NEXT = 112233; private volatile boolean isPlaying = false; private boolean lastIsPlayState = false; private int realPosition = -1; public RecyclerPagerView(Context context) { this(context,null); } public RecyclerPagerView(Context context, @Nullable AttributeSet attrs) { this(context, attrs,0); } public RecyclerPagerView(Context context, @Nullable AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); mRecyclerHandler = new Handler(Looper.getMainLooper(),this); } public void setOnPageChangeListener(OnPageChangeListener onPageChangeListener) { this.onPageChangeListener = onPageChangeListener; if(this.onPageChangeListener!=null){ addOnScrollListener(this.onPageChangeListener); int currentItem = getCurrentItem(); this.onPageChangeListener.onPageSelection(currentItem); } } public int getCurrentItem(){ LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager(); return linearLayoutManager.findFirstVisibleItemPosition(); } public void setCurrentItem(int position,boolean isAnimate){ Adapter adapter = getAdapter(); if(adapter==null || adapter.getItemCount()<=position){ return; } if(!isAnimate) { scrollToPosition(position); }else { smoothScrollToPosition(position); } } public void setCurrentItem(int position ){ setCurrentItem(position,true); } @Override public boolean fling(int velocityX, int velocityY) { LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager(); int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels; // views on the screen int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition(); View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition); int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition(); View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition); // distance we need to scroll int leftMargin = (screenWidth - lastView.getWidth()) / 2; int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth(); int leftEdge = lastView.getLeft(); int rightEdge = firstView.getRight(); int scrollDistanceLeft = leftEdge - leftMargin; int scrollDistanceRight = rightMargin - rightEdge; int targetPosition; if (Math.abs(velocityX) < 1500) { // The fling is slow -> stay at the current page if we are less than half through, // or go to the next page if more than half through if (leftEdge > screenWidth / 2) { // go to next page smoothScrollBy(-scrollDistanceRight, 0); targetPosition = firstVisibleItemPosition; } else if (rightEdge < screenWidth / 2) { // go to next page smoothScrollBy(scrollDistanceLeft, 0); targetPosition = firstVisibleItemPosition+1; } else { // stay at current page if (velocityX > 0) { smoothScrollBy(-scrollDistanceRight, 0); } else { smoothScrollBy(scrollDistanceLeft, 0); } targetPosition = firstVisibleItemPosition; } } else { // The fling is fast -> go to next page if (velocityX > 0) { smoothScrollBy(scrollDistanceLeft, 0); targetPosition = firstVisibleItemPosition+1; } else { smoothScrollBy(-scrollDistanceRight, 0); targetPosition = firstVisibleItemPosition; } } Log.e("RecyclerPagerView","nextPage="+targetPosition); if(this.onPageChangeListener!=null){ realPosition = targetPosition; this.onPageChangeListener.onPageSelection(targetPosition); } return true; } @Override public void onScrollStateChanged(final int state) { super.onScrollStateChanged(state); if (state == SCROLL_STATE_IDLE) { LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager(); int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels; int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition(); View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition); int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition(); View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition); // distance we need to scroll int leftMargin = (screenWidth - lastView.getWidth()) / 2; int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth(); int leftEdge = lastView.getLeft(); int rightEdge = firstView.getRight(); int scrollDistanceLeft = leftEdge - leftMargin; int scrollDistanceRight = rightMargin - rightEdge; int targetPosition = -1; if (leftEdge > screenWidth / 2) { smoothScrollBy(-scrollDistanceRight, 0); targetPosition = firstVisibleItemPosition+1; } else if (rightEdge < screenWidth / 2) { smoothScrollBy(scrollDistanceLeft, 0); targetPosition = lastVisibleItemPosition; }else{ targetPosition = firstVisibleItemPosition; } if(this.onPageChangeListener!=null){ realPosition = targetPosition; this.onPageChangeListener.onPageSelection(targetPosition); } } } @Override public boolean handleMessage(Message msg) { int what = msg.what; switch (what){ case MSG_PLAY_NEXT: showNextPage(); break; } return false; } private void showNextPage() { if(!isPlaying){ return; } if(!canRecyclePlaying()){ isPlaying = false; return; } Adapter adapter = getAdapter(); int currentItem = getCurrentItem(); if(adapter!=null && adapter.getItemCount()>0) { if (currentItem == NO_POSITION ) { setCurrentItem(0); }else { setCurrentItem(currentItem+1); } } mRecyclerHandler.sendEmptyMessageDelayed(MSG_PLAY_NEXT,TASK_TIMEOUT); } public void startPlay(){ if(isPlaying){ stopPlay(); } if (!canRecyclePlaying()){ isPlaying = false; return; } isPlaying = true; mRecyclerHandler.sendEmptyMessageDelayed(MSG_PLAY_NEXT,TASK_TIMEOUT); } @Override public void setAdapter(Adapter adapter) { super.setAdapter(adapter); if(canRecyclePlaying()){ if(realPosition==-1){ realPosition = 1000; } setCurrentItem(realPosition,false); } } private boolean canRecyclePlaying() { Adapter adapter = getAdapter(); if(adapter==null || adapter.getItemCount()<1) return false; return true; } private void stopPlay() { isPlaying = false; mRecyclerHandler.removeMessages(MSG_PLAY_NEXT); } @Override protected void onAttachedToWindow() { super.onAttachedToWindow(); if(lastIsPlayState){ startPlay(); } } @Override protected void onDetachedFromWindow() { super.onDetachedFromWindow(); lastIsPlayState = isPlaying; stopPlay(); } public static abstract class OnPageChangeListener extends RecyclerView.OnScrollListener{ public abstract void onPageSelection(int position); }}
Adapter+Holder 适配器
该类的作用主要用于约束和快速接入
public class QuickViewHolder extends RecyclerView.ViewHolder{ private SparseArray mViews; private View mConvertView; private QuickViewHolder(View v){ super(v); mConvertView = v; mViews = new SparseArray<>(); } public static QuickViewHolder get(ViewGroup parent, int layoutId){ View convertView = LayoutInflater.from(parent.getContext()).inflate(layoutId, parent, false); return new QuickViewHolder(convertView); } public T getView(int id){ View v = mViews.get(id); if(v == null){ v = mConvertView.findViewById(id); mViews.put(id, v); } return (T)v; }}
BannerAdapter实现，该类继承QuickAdapter
public class BannerAdapter extends QuickAdapter{ public BannerAdapter(List datas) { super(datas); } @Override public int getLayoutId(int viewType) { return R.layout.item_banner_image; } @Override public void convert(QuickViewHolder holder, String url, int position) { final Resources resources = holder.itemView.getResources(); final int drawableId = resources.getIdentifier(url, "drawable", holder.itemView.getContext().getPackageName()); if(drawableId!=0) { ImageView bannerImage = holder.getView(R.id.banner_image_item); bannerImage.setImageResource(drawableId); } }}
三、使用
final RecyclerPagerView rpv = findViewById(R.id.recycler_pager); tipTextView = findViewById(R.id.tip_text); LinearLayoutManager lm = new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false); rpv.setLayoutManager(lm); Listimagelist = new ArrayList<>(); imagelist.add("banner_t1"); imagelist.add("banner_t2"); imagelist.add("banner_t3"); imagelist.add("banner_t4"); rpv.setAdapter(new BannerAdapter(imagelist)); rpv.setOnPageChangeListener(new PagerChangeListener(tipTextView,imagelist.size())); rpv.startPlay();
监听器
public static class PagerChangeListener extends RecyclerPagerView.OnPageChangeListener { private TextView tipTextView; private int size; public PagerChangeListener(TextView tipTextView,int size) { this.tipTextView = tipTextView; this.size = size; } @Override public void onPageSelection(int position) { tipTextView.setText((position%size+1)+"/"+size); } }