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 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);
List 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);
}
}