ViewPager 实现 Galler 效果, 中间大图显示，两边小图展示（优化篇）
来源：互联网 发布：阿里云学生服务器搭建 编辑：程序博客网 时间：2024/05/01 09:17
上一张效果图：
之前的项目有一个Galley的项目，但是代码结构特别乱，别问我为什么，我也是刚接手这个项目，为了方便以后阅读和维护我对一些模块进行了重构。ViewPager实现Galler效果，但是当时时间比较急，写的比较仓促，上一篇实现了简单的效果，但是对于初始的时候左边滑动是有问题的，这是因为我们在自己的Adapter的时候对于getCount，我们想通过Integer.MAX_VALUE来实现无限循环，简单的说这个是向右（无限大）吧，所以也就只是实现了向右的循环，对于像左的还是不行的。
那么怎么解决呢？
首先我们对Adapter还是需要按以前的写法，其实Adapter适配器就是帮我们做界面的，其他的逻辑最好不要加，我之前的想法是用过
viewPager.addOnPageChangeListener来实现，通过判断是否滑到最左边或者最右边来实现循环滑到。
int realPosition = mAdapter.toRealPosition(position); if (mPreviousPosition != realPosition) { mPreviousPosition = realPosition; if (mOuterPageChangeListener != null) { mOuterPageChangeListener.onPageSelected(realPosition); } }
这里我封装了一个类，只要将你的ViewPager改为我封装好的ViewPager就行
LoopViewPager
public class LoopViewPager extends ViewPager { private static final boolean DEFAULT_BOUNDARY_CASHING = false; private OnPageChangeListener mOuterPageChangeListener; private LoopPagerAdapterWrapper mAdapter; private boolean mBoundaryCaching = DEFAULT_BOUNDARY_CASHING; public static int toRealPosition( int position, int count ){ position = position-1; if( position < 0 ){ position += count; }else{ position = position%count; } return position; } public void setBoundaryCaching(boolean flag) { mBoundaryCaching = flag; if (mAdapter != null) { mAdapter.setBoundaryCaching(flag); } } @Override public void setAdapter(PagerAdapter adapter) { mAdapter = new LoopPagerAdapterWrapper(adapter); mAdapter.setBoundaryCaching(mBoundaryCaching); super.setAdapter(mAdapter); setCurrentItem(0, false); } @Override public PagerAdapter getAdapter() { return mAdapter != null ? mAdapter.getRealAdapter() : mAdapter; } @Override public int getCurrentItem() { return mAdapter != null ? mAdapter.toRealPosition(super.getCurrentItem()) : 0; } public void setCurrentItem(int item, boolean smoothScroll) { int realItem = mAdapter.toInnerPosition(item); super.setCurrentItem(realItem, smoothScroll); } @Override public void setCurrentItem(int item) { if (getCurrentItem() != item) { setCurrentItem(item, true); } } @Override public void setOnPageChangeListener(OnPageChangeListener listener) { mOuterPageChangeListener = listener; }; public LoopViewPager(Context context) { super(context); init(); } public LoopViewPager(Context context, AttributeSet attrs) { super(context, attrs); init(); } private void init() { super.setOnPageChangeListener(onPageChangeListener); } private OnPageChangeListener onPageChangeListener = new OnPageChangeListener() { private float mPreviousOffset = -1; private float mPreviousPosition = -1; @Override public void onPageSelected(int position) { int realPosition = mAdapter.toRealPosition(position); if (mPreviousPosition != realPosition) { mPreviousPosition = realPosition; if (mOuterPageChangeListener != null) { mOuterPageChangeListener.onPageSelected(realPosition); } } } @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { int realPosition = position; if (mAdapter != null) { realPosition = mAdapter.toRealPosition(position); if (positionOffset == 0 && mPreviousOffset == 0 && (position == 0 || position == mAdapter.getCount() - 1)) { setCurrentItem(realPosition, false); } } mPreviousOffset = positionOffset; if (mOuterPageChangeListener != null) { if (realPosition != mAdapter.getRealCount() - 1) { mOuterPageChangeListener.onPageScrolled(realPosition, positionOffset, positionOffsetPixels); } else { if (positionOffset > .5) { mOuterPageChangeListener.onPageScrolled(0, 0, 0); } else { mOuterPageChangeListener.onPageScrolled(realPosition, 0, 0); } } } } @Override public void onPageScrollStateChanged(int state) { if (mAdapter != null) { int position = LoopViewPager.super.getCurrentItem(); int realPosition = mAdapter.toRealPosition(position); if (state == ViewPager.SCROLL_STATE_IDLE && (position == 0 || position == mAdapter.getCount() - 1)) { setCurrentItem(realPosition, false); } } if (mOuterPageChangeListener != null) { mOuterPageChangeListener.onPageScrollStateChanged(state); } } };}LoopPagerAdapterWrapperpublic class LoopPagerAdapterWrapper extends PagerAdapter { private PagerAdapter mAdapter; private SparseArray<ToDestroy> mToDestroy = new SparseArray<ToDestroy>(); private boolean mBoundaryCaching; void setBoundaryCaching(boolean flag) { mBoundaryCaching = flag; } LoopPagerAdapterWrapper(PagerAdapter adapter) { this.mAdapter = adapter; } @Override public void notifyDataSetChanged() { mToDestroy = new SparseArray<ToDestroy>(); super.notifyDataSetChanged(); } int toRealPosition(int position) { int realCount = getRealCount(); if (realCount == 0) return 0; int realPosition = (position-1) % realCount; if (realPosition < 0) realPosition += realCount; return realPosition; } public int toInnerPosition(int realPosition) { int position = (realPosition + 1); return position; } private int getRealFirstPosition() { return 1; } private int getRealLastPosition() { return getRealFirstPosition() + getRealCount() - 1; } @Override public int getCount() { return mAdapter.getCount() + 2; } public int getRealCount() { return mAdapter.getCount(); } public PagerAdapter getRealAdapter() { return mAdapter; } @Override public Object instantiateItem(ViewGroup container, int position) { int realPosition = (mAdapter instanceof FragmentPagerAdapter || mAdapter instanceof FragmentStatePagerAdapter) ? position : toRealPosition(position); if (mBoundaryCaching) { ToDestroy toDestroy = mToDestroy.get(position); if (toDestroy != null) { mToDestroy.remove(position); return toDestroy.object; } } return mAdapter.instantiateItem(container, realPosition); } @Override public void destroyItem(ViewGroup container, int position, Object object) { int realFirst = getRealFirstPosition(); int realLast = getRealLastPosition(); int realPosition = (mAdapter instanceof FragmentPagerAdapter || mAdapter instanceof FragmentStatePagerAdapter) ? position : toRealPosition(position); if (mBoundaryCaching && (position == realFirst || position == realLast)) { mToDestroy.put(position, new ToDestroy(container, realPosition, object)); } else { mAdapter.destroyItem(container, realPosition, object); } } @Override public void finishUpdate(ViewGroup container) { mAdapter.finishUpdate(container); } @Override public boolean isViewFromObject(View view, Object object) { return mAdapter.isViewFromObject(view, object); } @Override public void restoreState(Parcelable bundle, ClassLoader classLoader) { mAdapter.restoreState(bundle, classLoader); } @Override public Parcelable saveState() { return mAdapter.saveState(); } @Override public void startUpdate(ViewGroup container) { mAdapter.startUpdate(container); } @Override public void setPrimaryItem(ViewGroup container, int position, Object object) { mAdapter.setPrimaryItem(container, position, object); } static class ToDestroy { ViewGroup container; int position; Object object; public ToDestroy(ViewGroup container, int position, Object object) { this.container = container; this.position = position; this.object = object; } }}
这里需要注意对于上一篇的WelfareAdapter ，我们就按常规写法就行。public class WelfareAdapter extends PagerAdapter { private Context mContext; private List<PanicBean> dataList = new ArrayList<>(); public WelfareAdapter(Context mContext) { this.mContext = mContext; } public void setDatas(List<PanicBean> list) { if (list.size() <= 0) { dataList.clear(); notifyDataSetChanged(); return; } dataList.clear(); dataList.addAll(list); notifyDataSetChanged(); } @Override public int getCount() { return /*Integer.MAX_VALUE*/dataList.size(); } @Override public int getItemPosition(Object object) { return POSITION_NONE; } @Override public void destroyItem(View container, int position, Object object) { } @Override public Object instantiateItem(ViewGroup container, int position) {// position %= dataList.size();// if (position<0){// position = dataList.size()+position;// } PanicBean data = dataList.get(position); ViewHolder viewHolder = null; View view = LayoutInflater.from(mContext).inflate( R.layout.item_finefare_layout, null); if (viewHolder == null) { viewHolder = new ViewHolder(view); } bindView(viewHolder, data); container.addView(view, LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT); return view; } private void bindView(ViewHolder viewholder, final PanicBean data) { Glide.with(mContext).load(data.pic).into(viewholder.welfareImage); viewholder.welfareImage.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { ToastUtils.showToast("你点击了"+data.href); } }); } @Override public boolean isViewFromObject(View view, Object object) { return view == object; } @Override public void destroyItem(ViewGroup container, int position, Object object) { container.removeView((View) object); } class ViewHolder { @BindView(R.id.welfare_image) RoundedImageView welfareImage; ViewHolder(View view) { ButterKnife.bind(this, view); view.setTag(this); } public void reset() { welfareImage.setBackground(mContext.getResources().getDrawable(R.drawable.welfare_default_icon)); } }}
部分源码：https://github.com/xiangzhihong/jingdongApp
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