ViewPager 可回收的adapter

短命女 2022-08-18 05:52 128阅读 0赞

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][http_www.cnblogs.com_maoyu417_p_3740209.html]

[http_www.cnblogs.com_maoyu417_p_3740209.html]: http://www.cnblogs.com/maoyu417/p/3740209.html