Android 使用RecyclerView实现轮播图

一、需求

之前一篇博客使用ViewPager实现轮播图《Android ViewPager实现循环轮播图》，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<View> 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 extends View> 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<String> {

    public BannerAdapter(List<String> 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);

        List<String> imagelist = 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);
        }
    }