一、原理

ViewPager是Android中使用频率相对较高的view组件，同时对滑动过程中的事件进行了处理，因此非常适合轮播图。关于轮播图的实现，有很多方法，使用HorizontalView或者RecylerView也可以实现，但是需要处理fling操作，这里我们用ViewPager避免这些工作。

网上有很多关于ViewPager轮播的轮播实现，其原理大多数给PagerAdapter的getCount 放大N倍，N大于100,1000等。这里我们使用另一种思路，数据映射。

数据映射方案：

假设原始数据有N张图片数据，我们将数据N+2，然后将原来的第一张图片放到新的 索引为N+1的位置，原来的最后一张图片放到第一张图片，这样构建了一个新的数据。

当图片滑动到 position==0 时，我们使用viewPager.setCurrentItem(N,false) ，当position=N+1时，我们使用viewPager.setCurrentItem(1,false);便可实无限滑动。

当然，以上方案可行，也很简单，但是却破坏了原始数据，我们可以通过算法实现原始数据不被破坏的实现方式，计算出真实的数据索引。

 private int getRealPosition(int position) {            int realPosition = position;            if(InnerWrapperPagerAdapter.this.getCount()>1){                if(position==0){                    realPosition = (getCount()-2)-1;                }else if(position==getCount()-1){                    realPosition = 0;                }else{                    realPosition = position-1;                }            }            return realPosition;        }

二、代码实现

public class AutoBannerView extends ViewPager implements Handler.Callback {    private OnPagerChangeListener mOpageChangeListener;    public static long TIME_WAIT = 3000;  //每3秒轮播一次    private boolean isPlaying = false;    private OnPagerSelectedListener mOnPagerSelectedListener;    private boolean lastStateIsPlaying = false; //停止轮播之前的状态    //private   static  AutoBannerRunnable autoRunnable = null;    private final  Handler  mTaskHandler;    private static final int ACTION_PLAY = 1024*1024;    public AutoBannerView(Context context) {        this(context,null);    }    public AutoBannerView(Context context, AttributeSet attrs) {        super(context, attrs);        setOverScrollMode(OVER_SCROLL_NEVER);        setOffscreenPageLimit(5);        if(mOpageChangeListener==null){            mOpageChangeListener = new OnPagerChangeListener(this);        }        mTaskHandler = new Handler(Looper.getMainLooper(),this);    }    public void setOnPagerSelectedListener(OnPagerSelectedListener mOnPagerSelectedListener) {        this.mOnPagerSelectedListener = mOnPagerSelectedListener;    }    @Override    public boolean addViewInLayout(View child, int index, ViewGroup.LayoutParams params) {        return super.addViewInLayout(child, index, params);    }    @Override    protected boolean addViewInLayout(View child, int index, ViewGroup.LayoutParams params, boolean preventRequestLayout) {        return super.addViewInLayout(child, index, params, preventRequestLayout);    }    @Override    public void setAdapter(PagerAdapter adapter) {        if (null != getAdapter()) {            removeOnPageChangeListener(mOpageChangeListener);        }        if (null == adapter) {            super.setAdapter(null);        } else {            super.setAdapter(new InnerWrapperPagerAdapter(adapter,this));            addOnPageChangeListener(mOpageChangeListener);            if(adapter.getCount()>1){                setCurrentItem(1,false);  //getCount>1 ,初始化时默认显示原始数据的第0位，也就是新的PagerAdapter的第二位                startPlay();            }else if(adapter.getCount()>0){                mOpageChangeListener.onPageSelected(0);            }        }    }    @Override    public boolean onTouchEvent(MotionEvent ev) {        finishResetPosition();        final ViewParent parent = this.getParent();        switch (ev.getActionMasked()){            case MotionEvent.ACTION_DOWN:            case MotionEvent.ACTION_MOVE:                if (parent != null) {                    parent.requestDisallowInterceptTouchEvent(true);                    //解决ViewPager嵌套ViewPager导致无法滑动的问题                }                if(isPlaying){                    stopPlay();                }                break;            case MotionEvent.ACTION_UP:            case MotionEvent.ACTION_CANCEL:                if (parent != null) {                    parent.requestDisallowInterceptTouchEvent(false);                    //解决ViewPager嵌套ViewPager导致无法滑动的问题                }                if(lastStateIsPlaying){                    startPlay();                }                break;        }        return super.onTouchEvent(ev);    }    public PagerAdapter getRealAdapter() {        final PagerAdapter adapter = getAdapter();        if( adapter instanceof  InnerWrapperPagerAdapter){            return ((InnerWrapperPagerAdapter) adapter).getTargetPagerAdapter();        }        return adapter;    }    public static class AdapterDataSetObserver extends  DataSetObserver{        private InnerWrapperPagerAdapter  innerWrapperPagerAdapter;        private AutoBannerView autoBannerView;        public AdapterDataSetObserver(InnerWrapperPagerAdapter innerWrapperPagerAdapter,AutoBannerView autoBannerView) {            this.innerWrapperPagerAdapter = innerWrapperPagerAdapter;            this.autoBannerView  = autoBannerView;        }        @Override        public void onChanged() {            super.onChanged();            innerWrapperPagerAdapter.notifyDataSetChanged();            if(innerWrapperPagerAdapter.getCount()>1){                final int currentItem = this.autoBannerView.getCurrentItem();                if(currentItem==0){                    this.autoBannerView.setCurrentItem(1,false);                }                if(this.autoBannerView.isPlaying || this.autoBannerView.lastStateIsPlaying){                    this.autoBannerView.startPlay();                }            }            if(innerWrapperPagerAdapter.getCount()>0 &&this.autoBannerView.mOpageChangeListener!=null) {                this.autoBannerView.mOpageChangeListener.onPageSelected(this.autoBannerView.getCurrentItem());            }        }    }    /**     * 包装PagerAdapter，实现数据映射     */    private static class  InnerWrapperPagerAdapter extends PagerAdapter{        private final AdapterDataSetObserver adapterDataSetObserver;        private PagerAdapter mPagerAdapter;        public InnerWrapperPagerAdapter(PagerAdapter pagerAdapter,AutoBannerView autoBannerView) {            this.mPagerAdapter = pagerAdapter;            this.adapterDataSetObserver = new AdapterDataSetObserver(this,autoBannerView);            if(this.mPagerAdapter!=null){                this.mPagerAdapter.registerDataSetObserver(this.adapterDataSetObserver);            }        }        public PagerAdapter getTargetPagerAdapter() {            return mPagerAdapter;        }        @Override        public int getCount() {            if(mPagerAdapter!=null) {  //如果数据大于1，说明可以轮播                return mPagerAdapter.getCount() > 1 ? mPagerAdapter.getCount() + 2 : mPagerAdapter.getCount();            }            return 0;        }        @Override        public boolean isViewFromObject(View view, Object object) {            if(mPagerAdapter!=null) {                return mPagerAdapter.isViewFromObject(view, object);            }            return false;        }        @Override        public Object instantiateItem(ViewGroup container, int position) {            if(mPagerAdapter!=null) {                int realPosition = getRealPosition(position);                return mPagerAdapter.instantiateItem(container, realPosition);            }            return super.instantiateItem(container,position);        }        @Override        public void destroyItem(ViewGroup container, int position, Object object) {            if(mPagerAdapter!=null) {                int realPosition = getRealPosition(position);                mPagerAdapter.destroyItem(container, realPosition, object);            }else{                super.destroyItem(container,position,object);            }        }        private int getRealPosition(int position) {            int realPosition = position;            if(InnerWrapperPagerAdapter.this.getCount()>1){                if(position==0){                    realPosition = (getCount()-2)-1;                }else if(position==getCount()-1){                    realPosition = 0;                }else{                    realPosition = position-1;                }            }            return realPosition;        }        @Override        public int getItemPosition(Object object) {            if(mPagerAdapter!=null){                return mPagerAdapter.getItemPosition(object);            }            return super.getItemPosition(object);        }        @Override        public CharSequence getPageTitle(int position) {            if(mPagerAdapter!=null) {                int realPosition = getRealPosition(position);                return mPagerAdapter.getPageTitle(realPosition);            }else{                return super.getPageTitle(position);            }        }        @Override        public float getPageWidth(int position) {            if(mPagerAdapter!=null){                int realPosition = getRealPosition(position);                return mPagerAdapter.getPageWidth(realPosition);            }            return super.getPageWidth(position);        }        @Override        public void startUpdate(ViewGroup container) {            if(mPagerAdapter!=null) {                mPagerAdapter.startUpdate(container);            }else{                super.startUpdate(container);            }        }        @Override        public void setPrimaryItem(ViewGroup container, int position, Object object) {            if(mPagerAdapter!=null) {                int realPosition = getRealPosition(position);                mPagerAdapter.setPrimaryItem(container, realPosition, object);            }else{                super.setPrimaryItem(container,position,object);            }        }        @Override        public void finishUpdate(ViewGroup container) {            if(mPagerAdapter!=null)            {                mPagerAdapter.finishUpdate(container);            }else{                super.finishUpdate(container);            }        }        @Override        public Parcelable saveState() {            if(mPagerAdapter!=null)            {                return mPagerAdapter.saveState();            }            return super.saveState();        }        @Override        public void restoreState(Parcelable state, ClassLoader loader) {            if(mPagerAdapter!=null) {                mPagerAdapter.restoreState(state, loader);            }else{                super.restoreState(state,loader);            }        }        public void setPagerAdapter(PagerAdapter pagerAdapter) {            this.mPagerAdapter = pagerAdapter;        }    }    public int getClientWidth(){        return getMeasuredWidth() - getPaddingLeft() - getPaddingRight();    }    private static class OnPagerChangeListener implements ViewPager.OnPageChangeListener{        private final AutoBannerView mAutoBannerView;        public OnPagerChangeListener(AutoBannerView autoBannerView) {            this.mAutoBannerView = autoBannerView;        }        @Override        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {            if(shouldCancelHandle()) return;        }        @Override        public void onPageSelected(int position) {            if(shouldCancelHandle()) return;              notifyUpdateIndictor(position);        }        public void notifyUpdateIndictor(int position) {            final int realPosition = getRealPosition(position);            if(this.mAutoBannerView.mOnPagerSelectedListener!=null){                final PagerAdapter adapter = this.mAutoBannerView.getAdapter();                final int count = adapter.getCount();                if(count>1) {                    this.mAutoBannerView.mOnPagerSelectedListener.onPagerItemSelected(realPosition);                }else if(count==1){                    this.mAutoBannerView.mOnPagerSelectedListener.onPagerItemSelected(1);                }else{                    this.mAutoBannerView.mOnPagerSelectedListener.onPagerItemSelected(0);                }            }        }        private int getRealPosition(int position) {            int realPosition = position;            if(this.mAutoBannerView .getAdapter().getCount()>1){                PagerAdapter adapter = this.mAutoBannerView.getAdapter();  //1                if(adapter instanceof InnerWrapperPagerAdapter){                    adapter =   ((InnerWrapperPagerAdapter) adapter).getTargetPagerAdapter();                }                if(position==0){                    realPosition = adapter.getCount();                }else if(position==adapter.getCount()+1){                    realPosition = 1;                }            }            return realPosition;        }        @Override        public void onPageScrollStateChanged(int state) {            //在该方法中处理首尾切换，其他方法会产生动画中断问题            if(shouldCancelHandle()) return;            if(state!=SCROLL_STATE_IDLE){ //当动画执行完，立即切换                this.mAutoBannerView.finishResetPosition();            }        }        private boolean shouldCancelHandle() {            return this.mAutoBannerView==null || mAutoBannerView.getAdapter()==null;        }    }    @Override    protected void onAttachedToWindow() {        super.onAttachedToWindow();        if(lastStateIsPlaying){  //如果之前是轮播的，那么继续轮播            startPlay();        }    }    @Override    protected void onDetachedFromWindow() {        super.onDetachedFromWindow();        if(isPlaying) {            stopPlay();// 如果从window中移除掉，停止轮播        }        onInvisibleToUser();    }    private void onInvisibleToUser() {        final int currentItem = getCurrentItem();        PagerAdapter adapter = getAdapter();        if(adapter instanceof InnerWrapperPagerAdapter){            adapter =   ((InnerWrapperPagerAdapter) adapter).getTargetPagerAdapter();        }        if(adapter!=null && adapter.getCount()>1 && currentItem>0) {            setCurrentItem(currentItem - 1);            setCurrentItem(currentItem);        }    }    @Override    protected void onVisibilityChanged(View changedView, int visibility) {        super.onVisibilityChanged(changedView, visibility);        if (visibility == VISIBLE) {            if(lastStateIsPlaying){  //如果之前是轮播的，那么继续轮播                startPlay();            }        } else if (visibility == INVISIBLE || visibility == GONE) {            if(isPlaying) {                stopPlay();// 如果从window中移除掉，停止轮播            }            onInvisibleToUser();        }    }    public interface  OnPagerSelectedListener{        //用于监听真实的滑动位置，方便外部使用        public void onPagerItemSelected(int position);    }    public void startPlay(){        stopPlay();        isPlaying = true;       /* postDelayed(autoRunnable,TIME_WAIT);*/        mTaskHandler.sendEmptyMessageDelayed(ACTION_PLAY,TIME_WAIT);    }    public void stopPlay() {        lastStateIsPlaying = isPlaying==true;        isPlaying = false;        mTaskHandler.removeMessages(ACTION_PLAY);    }    @Override    public boolean handleMessage(Message msg) {        if(msg==null) return false;        int action = msg.what;        switch (action){            case ACTION_PLAY:                this.showNext();                return  true;        }        return false;    }    private long lastExecuteTimestramp = 0;    private boolean finishResetPosition() {        if(!(this.getAdapter() instanceof InnerWrapperPagerAdapter)) return false;        int currentItem = this.getCurrentItem();        if(this.getAdapter().getCount()>1){            InnerWrapperPagerAdapter adapter = (InnerWrapperPagerAdapter) this.getAdapter();            if(currentItem==0 ){                //this.setCurrentItem(adapter.getCount()-2,false);                scrollToItem(adapter.getCount()-2,adapter.getCount());                return  true;            }else if(currentItem==adapter.getCount()-1){                scrollToItem(1,adapter.getCount());              /*  this.setCurrentItem(1,false)*/;                return true;            }        }        return false;    }    public void showNext() {        if(Looper.myLooper()!=Looper.getMainLooper()) return; //要求在主线程工作        final long currentTimestramp = System.currentTimeMillis();        final long diff = (currentTimestramp - lastExecuteTimestramp);        lastExecuteTimestramp = currentTimestramp;        PagerAdapter adapter = this.getAdapter();        if(null==adapter || adapter.getCount()<=1) return;        if(!this.isPlaying) return; //停止执行        int currentItem = this.getCurrentItem();        if (currentItem > 0 && currentItem < (adapter.getCount() - 1)) {            if(currentItem==1){                scrollToItem(1,adapter.getCount());            }            this.setCurrentItem(currentItem + 1, true);        }        if(diff

public class SlidingBanner extends RelativeLayout implements AutoBannerView.OnPagerSelectedListener {    private AutoBannerView mAutoPlayViewPager;    private TextView mPositionTextView;    private OnPagerItemClickListener onPagerItemClickListener;    private ImageView.ScaleType scaleType = ImageView.ScaleType.FIT_XY;    private RotationPageTransformer pageTransformer;    private int offscreenPageLimit;    private int pageMargin;    public SlidingBanner(Context context) {        this(context,null);    }    public SlidingBanner(Context context, AttributeSet attrs) {        this(context, attrs,0);    }    public SlidingBanner(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        setScaleType(ImageView.ScaleType.FIT_XY);    }    public void setOnPagerItemClickListener(OnPagerItemClickListener onPagerItemClickListener) {        this.onPagerItemClickListener = onPagerItemClickListener;    }    public void setImageList(List imageList){        if(imageList==null){            imageList = new ArrayList<>();        }        if( !(mAutoPlayViewPager.getRealAdapter() instanceof SlidingPagerAdapter) ){            setPagerAdapter(new SlidingPagerAdapter(this, imageList));        }else{            SlidingPagerAdapter slidingPagerAdapter = (SlidingPagerAdapter) mAutoPlayViewPager.getRealAdapter();            slidingPagerAdapter.updateDatasource(imageList);        }    }    public boolean isEmptyBanner(){        if(mAutoPlayViewPager==null || mAutoPlayViewPager.getRealAdapter()==null){            return true;        }        return false;    }    public void hidePositionIndictor(){        if(mPositionTextView!=null) {            mPositionTextView.setVisibility(GONE);        }    }    public void showPositionIndictor(){        if(mPositionTextView!=null) {            mPositionTextView.setVisibility(VISIBLE);        }    }    public void setPagerAdapter(PagerAdapter pagerAdapter) {        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.setAdapter(pagerAdapter);        }    }    public PagerAdapter getPagerAdapter( ) {        return mAutoPlayViewPager.getRealAdapter();    }    @Override    protected void onFinishInflate() {        super.onFinishInflate();        if(mAutoPlayViewPager==null) {            mAutoPlayViewPager = createAutoPlayViewPager();            addView(mAutoPlayViewPager,0);        }        if(mPositionTextView ==null){            mPositionTextView = createPositionTextView();            addView(mPositionTextView,1);        }        mAutoPlayViewPager.setOnPagerSelectedListener(this);    }    private TextView createPositionTextView() {        TextView tv = new AppCompatTextView(this.getContext());        LayoutParams lp = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);        lp.addRule(ALIGN_PARENT_BOTTOM);        lp.addRule(ALIGN_PARENT_RIGHT);        lp.rightMargin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,8,getResources().getDisplayMetrics());        lp.bottomMargin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,4,getResources().getDisplayMetrics());        PaintDrawable shapeDrawable = new PaintDrawable(0xAA000000);        shapeDrawable.setCornerRadius(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,8,getResources().getDisplayMetrics()));        tv.setBackground(shapeDrawable);        final int px = DisplayUtil.dp2px(getContext(), 8);        tv.setPadding(px,0,px,0);        tv.setLayoutParams(lp);        tv.setTextColor(Color.WHITE);        tv.setTextSize(12);        return  tv;    }    private AutoBannerView createAutoPlayViewPager() {        AutoBannerView autoPlayViewPager = new AutoBannerView(getContext());        LayoutParams lp = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);        autoPlayViewPager.setLayoutParams(lp);        if(this.pageTransformer!=null){            autoPlayViewPager.setPageTransformer(true,this.pageTransformer);        }        if(this.offscreenPageLimit!=0){            autoPlayViewPager.setOffscreenPageLimit(this.offscreenPageLimit);        }        autoPlayViewPager.setPageMargin(this.pageMargin);        return autoPlayViewPager;    }    @Override    public void onPagerItemSelected(int position) {        if(mAutoPlayViewPager==null || mAutoPlayViewPager.getRealAdapter()==null) return;        final PagerAdapter adapter = mAutoPlayViewPager.getRealAdapter();        updateIndictor(position,adapter.getCount());    }    private void updateIndictor(int position,int count) {        if(mPositionTextView==null) return;        mPositionTextView.setText(String.format("%s/%s",position,count));    }    public ImageView.ScaleType getScaleType() {        return scaleType;    }    public void setScaleType(ImageView.ScaleType scaleType) {        this.scaleType = scaleType;    }    public void startPlay() {        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.startPlay();        }    }    public void stopPlay(){        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.stopPlay();        }    }    public void setPageTransformer(RotationPageTransformer pageTransformer) {        this.pageTransformer = pageTransformer;        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.setPageTransformer(true,pageTransformer);        }    }    public void setOffscreenPageLimit(int offscreenPageLimit) {        this.offscreenPageLimit = offscreenPageLimit;        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.setOffscreenPageLimit(this.offscreenPageLimit);        }    }    public void setPageMargin(int pageMargin) {        this.pageMargin = pageMargin;        if(mAutoPlayViewPager!=null){            mAutoPlayViewPager.setPageMargin(20);        }    }    @Override    protected void onAttachedToWindow() {        super.onAttachedToWindow();       // notifyImageViewInvalidate();    }    private void notifyImageViewInvalidate() {        if(mAutoPlayViewPager==null) return;        final List imageViews = AppUtils.getViews(mAutoPlayViewPager, ImageView.class);        if(imageViews==null || imageViews.size()==0) return;        for (ImageView imageView : imageViews){            if(imageView==null || imageView.getVisibility()==GONE) continue;            final Drawable drawable = imageView.getDrawable();            if(drawable==null){                imageView.setImageResource(R.drawable.defualt_img);            }else {                if (!drawable.isVisible()) {                    drawable.setVisible(true, false);                }else {                    drawable.invalidateSelf();                }            }        }    }    public final static  class  SlidingPagerAdapter  extends PagerAdapter{        private final SlidingBanner slidingBanner;        private List  imagelst;        public SlidingPagerAdapter(SlidingBanner slidingBanner, List  images){            this.slidingBanner = slidingBanner;            this.imagelst = new ArrayList<>();            this.imagelst.addAll(images);        }        @Override        public void startUpdate(ViewGroup container) {            super.startUpdate(container);            container.setEnabled(false);        }        @Override        public void finishUpdate(ViewGroup container) {            super.finishUpdate(container);            container.requestLayout();            container.invalidate();            container.setEnabled(true);        }        @Override        public int getItemPosition(Object object) {            return PagerAdapter.POSITION_NONE;        }        @Override        public int getCount() {            return imagelst.size();        }        @Override        public boolean isViewFromObject(View view, Object object) {            return view==object;        }        @Override        public Object instantiateItem(ViewGroup container, int position) {            View view = getView(container, position);            if(view.getParent()!= null){                final ViewGroup parent = ((ViewGroup)view.getParent());                parent.removeViewInLayout(view);            }            if(container instanceof AutoBannerView) {                ((AutoBannerView) container).addViewInLayout(view,-1,view.getLayoutParams());            }else{                container.addView(view);            }            addOnClickListenerToView(view,position,container);            return view;        }        private void addOnClickListenerToView(View view,int position ,ViewGroup container) {            view.setOnClickListener(new OnClickListener() {                @Override                public void onClick(View v) {                    int childIndex = position;                    if(slidingBanner.onPagerItemClickListener!=null) {                        slidingBanner.onPagerItemClickListener.onPagerItemClick(childIndex,view,container);                    }                }            });        }        private View getView(ViewGroup container,int position){            final LayoutInflater inflater = LayoutInflater.from(container.getContext());            final ImageView view = getImageView(inflater, position);           Glide.with(view).diskCacheStrategy(DiskCacheStrategy.ALL).load(imagelst.get(position)).placeholder(R.drawable.xsj_default_product_img).into(view);            return  view;        }        private ImageView getImageView(LayoutInflater inflater, int position) {            ImageView imageView = new AppImageView(inflater.getContext());            imageView.setImageResource(R.drawable.xsj_default_product_img);            ViewPager.LayoutParams lp = new ViewPager.LayoutParams();            imageView.setLayoutParams(lp);            if(slidingBanner.getScaleType()!=null){                imageView.setScaleType(slidingBanner.getScaleType());            }            return imageView;        }        @Override        public void destroyItem(ViewGroup container, int position, Object object) {            container.removeViewInLayout((View) object);        }        public void updateDatasource(List imageDataset) {            if(imageDataset==null || imageDataset.size()==0){                if(this.imagelst.size()>0){                    this.imagelst.clear();                    notifyDataSetChanged();                }                return;            }            if(this.imagelst.size()!=imageDataset.size()){                this.imagelst.clear();                this.imagelst.addAll(imageDataset);                notifyDataSetChanged();                return;            }            boolean isNeedUpdate = false;            for (int i=0;i

  slidingBanner.setImageList(entity);        slidingBanner.setOnPagerItemClickListener(this);        slidingBanner.startPlay();