ViewPager 可回收的adapter

虽说 ViewPager 以及 提供了 缓存的机制,

可以通过 mViewPager.setOffscreenPageLimit(4);

来设置缓存的页数

当然 还有一些特殊情况 为了性能的考略,  需要 回收一些View

而不是每次 缓存一页数据 都是从新加载.

其实也是 模仿ListView 的 holder 来缓存View 的

直接看代码吧: 

public class RecommendViewPageAdapter extends PagerAdapter {    public static final String TAG = "RecommendViewPageAdapter";    private Context mContext;    private List<TopicModel> mTopicModels;    private List<ViewHolder> mViewHolderList = new ArrayList<>();    public RecommendViewPageAdapter(Context context, List<TopicModel> models) {        mContext = context;        mTopicModels = models;    }    @Override    public int getCount() {        return mTopicModels.size();    }    @Override    public boolean isViewFromObject(View view, Object object) {        return view == ((ViewHolder) object).itemView;    }    @Override    public Object instantiateItem(ViewGroup container, int position) {        final ViewHolder viewHolder;        if (mViewHolderList.size() > 0) {            viewHolder = mViewHolderList.get(0);            mViewHolderList.remove(0);        } else {            final View item = LayoutInflater.from(mContext).inflate(R.layout.recommend_view_pager_item, null);            viewHolder = new ViewHolder(item);        }        final TopicModel headerTopic = mTopicModels.get(position);        viewHolder.mCoverImg.setImageURI(headerTopic.getBigCoverUri());        viewHolder.mTitleTxt.setText(headerTopic.getTitle());        viewHolder.mRankingTxt.setText(mContext.getResources().getString(R.string.ranking_count, headerTopic.getArticleNum()));        viewHolder.mFollowTxt.setText(mContext.getResources().getString(R.string.followed, headerTopic.getFollowUserNum()));        viewHolder.mTagsLinearLayout.removeAllViews();        for (int i = 0, z = headerTopic.getTagModelList().size(); i < z; i++) {            TextView tagTxtView = TagViewUtil.getTagTxtView(mContext);//            tagTxtView.setText("标签");            int padding = mContext.getResources().getDimensionPixelOffset(R.dimen.item_padding_micro);            int autoPadding = AutoUtils.scaleValue(padding);            AutoWrapLinearLayout.LayoutParams layoutParams = new AutoWrapLinearLayout.LayoutParams(autoPadding, autoPadding);            tagTxtView.setText(headerTopic.getTagModelList().get(i).getTag());            viewHolder.mTagsLinearLayout.addView(tagTxtView, layoutParams);        }        container.addView(viewHolder.itemView, -1, null);        if (mOnItemClickListener != null) {            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View v) {                    mOnItemClickListener.onClick(viewHolder.itemView, headerTopic, position);                }            });        }        return viewHolder;    }    public static class ViewHolder {        public View itemView;        @Bind(R.id.img_cover)        SimpleDraweeView mCoverImg;        @Bind(R.id.txt_title)        TextView mTitleTxt;        @Bind(R.id.tags_box)        AutoWrapLinearLayout mTagsLinearLayout;        @Bind(R.id.txt_ranking)        TextView mRankingTxt;        @Bind(R.id.txt_follow)        TextView mFollowTxt;        public ViewHolder(View itemView) {            this.itemView = itemView;            ButterKnife.bind(this, itemView);        }    }    @Override    public int getItemPosition(Object object) {        return POSITION_NONE;    }    @Override    public void destroyItem(ViewGroup container, int position, Object object) {        LogUtil.d(TAG, "destroyItem position = " + position + " , obj = " + object);        ViewHolder viewHolder = (ViewHolder) object;        (container).removeView(viewHolder.itemView);        mViewHolderList.add(viewHolder);        container.removeView(viewHolder.itemView);    }    OnItemClickListener mOnItemClickListener;    public void setOnItemClickListener(OnItemClickListener onItemClickListener) {        mOnItemClickListener = onItemClickListener;    }    public interface OnItemClickListener {        void onClick(View view, TopicModel headerTopic, int position);    }}

在 destroyItem 方法中  把View 缓存 

然后 instantiateItem 放在中 判断是否有缓存的View  有的话 重复利用

还有一点需要注意的是:

getItemPosition 方法 返回 POSITION_NONE,

再调用 adapter.notifyDataSetChanged() 时 才会 刷新整个ViewPager 会 destroy 调用所有Item 然后从新加载

关于  为什么返回 POSITION_NONE 可以产考 这片文章:

http://www.cnblogs.com/maoyu417/p/3740209.html